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Development of a mass spectrometry imaging system utilizing t-SPESI and its application to lipid imaging of tissue sections. The effects of solvent properties on the extraction-ionization process and the spatial resolution of ion images are discussed.

Current–voltage (I–V) nonlinearity is essential for information processing in molecular electronics. We used a nanoparticle bridge junction to investigate the effect of electronic coupling between ...

A sulfonated polyaniline (SPAN) organic electrochemical network device (OEND) is fabricated using a simple drop-casting method on multiple Au electrodes for use in reservoir computing (RC). The SPAN network has humidity-dependent electrical properties. Under high humidity, the SPAN OEND exhibits mainly ionic conduction, including charging of an electric double layer and ionic diffusion. The nonlinearity and hysteresis of the current-voltage characteristics progressively increase with increasing humidity. The rich dynamic output behavior indicates wide variations for each electrode, which improves the RC performance because of the disordered network. For RC, waveform generation and short-term memory tasks are realized by a linear combination of outputs. The waveform task accuracy and memory capacity calculated from a short-term memory task reach 90% and 33.9, respectively. Improved spoken-digit classification is realized with 60% accuracy by only 12 outputs, demonstrating that the SPAN OEND can manage time series dynamic data operation in RC owing to a combination of rich dynamic and nonlinear electronic properties. The results suggest that SPAN-based electrochemical systems can be applied for material-based computing, by exploiting their intrinsic physicochemical behavior.

A combination of direct liquid extraction using a small volume of solvent and electrospray ionization allows the rapid measurement of complex chemical components in biological samples and visualization of their distribution in tissue sections. This review describes the development of such techniques and their application to biological research since the first reports in the early 2000s. An overview of electrospray ionization, ion suppression in samples, and the acceleration of specific chemical reactions in charged droplets is also presented. Potential future applications for visualizing multimolecular environments in biological systems are discussed.

Liquid metals have attracted attention as functional components for moldable electronics, such as soft flexible connectors, wires or conductive ink. The relatively high surface tension (> 400 mN m−1) and the fact that liquid metals do not readily wet ceramic or oxide surfaces have led to devising unique techniques to spread the liquid and mold its shape. These techniques include surface modification, electrowetting and vacuum filling of channels. This work presents an injection technique based on pressurized fountain pen lithography with glass nanopipettes developed to directly pattern liquid metal on flat hard substrates. The liquid metals were eutectic alloys of Gallium, including Gallium-Indium (EGaIn), Gallium-Indium-Zinc and Gallium-Indium-Tin. The nanopipettes were coated internally with gold, acting as a sacrificial layer and facilitating the wetting of the pipette down to its pore, with an inner diameter of ~ 100–300 nm. By applying hydrodynamic pressure to the connected end of the pipette, the metal was extruded through the pore, forming long continuous (> 3 mm) and narrow (~ 1–15 µm) metal lines on silicon oxide and gold surfaces at room temperature and ambient conditions. With this robust platform, it is possible to pattern liquid metals on a variety of substrates and geometries down to the micron range.

Biological tissues are composed of a wide variety of chemical components, in which the amount and distribution of these components change dynamically according to health status. Mass spectrometry imaging (MSI) can be applied to biomedical research because of its ability to measure chemical components in a sample’s local area as a mass spectrum and visualize the chemical species distribution in a sample. This study reviewed the development of the tapping-mode scanning probe electrospray ionization (t-SPESI) technique to combine atomic force microscopy and mass spectrometry. t-SPESI uses a vibrating capillary probe to achieve rapid extraction, ionization, and MSI using picoliter solvents. Visualizing the distribution of disease-related components in the tissue was performed in the MSI of biological tissue. Multimodal imaging by t-SPESI was also demonstrated by implementing the optical detection of a probe vibration and the feedback control system into the t-SPESI.

The fabrication of molecular films by coating a conductive polymer solution on a substrate is an active topic in molecular electronics research. Since the inhomogeneity of polymer thin films modulates the chemical states and electrical properties of these films, the construction of integrated polymer devices requires methods to fabricate controllable, homogeneous molecular films as small patterns. Herein, we report the reproducible fabrication of sub-micrometer thickness self-doped polyaniline lines with high homogeneity by fountain-pen lithography (FPL). Compared with commonly used drop-casting and spin-coating methods, the fabrication of line patterns by FPL allows good control of line size, chemical/micro structures, and electronic properties, as demonstrated here by microscope Raman spectroscopy and conductance measurements. Supplying an identical amount of solution from a nanopipette and rapid solvent evaporation are likely crucial for fabricating homogeneous line patterns. This method is promising for the development of molecular electronic devices and the characterization of polymeric materials.

Kelvin probe force microscopy (KPFM) is a useful technique for simultaneously visualizing topography and contact potential difference (CPD). Although frequency-modulation (FM) KPFM has high spatial resolution and sensitivity, it is not readily applicable to measuring large protrusions owing to the instability of the feedback condition. Here we investigate the combined use of amplitude-modulation and FM for tip-sample distance control and electrostatic force detection, respectively. The proposed method enabled simultaneous acquisition of topography and CPD images of gold nanoparticles on a Nb-doped TiO2(100) surface. The effect of the tip shape and tilt angle on the CPD images is also discussed.

Electronic noise generators are an essential component of molecular neuromorphic devices. To realize molecular noise generators with a high degree of freedom for design and integration into molecular devices, the utilization of the local electric field for the modulation of electrical conduction via a shape-limited conductive polymer is one promising strategy. Herein, a molecular noise generator composed of thin self-doped polyaniline (SPAN) lines is reported. SPAN lines fabricated via fountain pen lithography on SiO2/Si substrates were found to generate current noise upon laser irradiation. This current noise exhibited white-noise-like power spectral density in the frequency range of 1–25 Hz and was independent of temperature. Multiple independent noise generation on the same substrate was also successfully demonstrated. The present results indicate that the noise generation mechanism involves the local modulation of hopping conduction via SPAN lines owing to the spatial proximity of the conduction path in the SPAN line to the surface photovoltage region of the SiO2/Si interface. This on-site random noise generation in shape-limited conductive polymers is expected to be beneficial for the realization of molecular neuromorphic devices.

Ambient sampling and ionization techniques based on direct liquid extraction and electrospray ionization are of great value for rapid analysis and mass spectrometry imaging. Scanning probe electrospray ionization (SPESI) enables the sampling and ionization of analyte molecules in a solid material using a liquid bridge and electrospray, respectively, from a single capillary probe. To further improve SPESI, it is essential to understand the dynamic behavior of nanoliter volumes of liquids during sampling and ionization. In this study, the dynamic formation and breakage of the liquid bridge and the subsequent electrospray ionization were investigated by measuring the displacement of the capillary probe using a new optical technique. Measurements revealed that both the time from the formation of the liquid bridge to its breakage and the time from the breakage of the liquid bridge to the detection of analyte ions were correlated with the physical properties of the solvent. It was also found that both of these times were positively correlated with the flow rate. These results will not only lead to the improvement of sampling and ionization efficiencies but also afford a greater understanding of the physicochemical properties of charged nanoliter volumes of liquids.

Nonlinear current–voltage (I–V) characteristics is an important property for the realization of information processing in molecular electronics. We studied the electrical conduction through a Ru–dye complex (N-719) on a 2-aminoethanethiol (2-AET) monolayer in a nanoparticle bridge junction system. The nonlinear I–V characteristics exhibited a threshold voltage at around 1.2 V and little temperature dependence. From the calculation of the molecular states using density functional theory and the energy alignment between the electrodes and molecules, the conduction mechanism in this system was considered to be resonant tunneling via the HOMO level of N-719. Our results indicate that the weak electronic coupling of electrodes and molecules is essential for obtaining nonlinear I–V characteristics with a clear threshold voltage that reflect the intrinsic molecular state.

Mass spectrometry imaging is an informative approach for the comprehensive analysis of multiple components inside biological specimens. We used novel tapping-mode scanning probe electrospray ionization mass spectrometry method to visualize cancer-related chemical components in the mouse pancreas tissue section at a sampling pitch of 100 µm. Positive ion mode measurements from m/z 100 to 1500 resulted in the visualization of multiple components that are tentatively assigned as polyamines, lipids and proteins. Their signal intensities inside the cancerous and the non-cancerous regions were found to be significantly different by the two-sample t-test.

We demonstrate multicolor, on-line visualization in label-free biomedical microscopy based on stimulated Raman scattering (SRS). Fast data acquisition of SRS spectral images and subsequent image generation are achieved. The loading vectors for the blind separation of chemical components are predetermined by multivariate analysis at a certain field of view (FOV) and are applied to execute on-line visualization of chemical images at other FOVs. We also show that the response time can be shortened by reducing the number of spectral data points. This on-line visualization system is expected to increase the usability of the Raman imaging system and the analytical throughput for screening.

Nonlinearity is the vital factor for stochastic computing. Toward the realization of brain-mimetic function using molecular network, the nonlinear electric properties of molecular systems are investigated in nanoscale with atomic force microscopy and nano-gap electrodes. Nonlinear current-voltage characteristics were observed for {Mo154/152}-ring, cytochorome c, and cytochrome c/DNA networks where the conduction paths include electron injection into weakly coupled discrete energy levels, electron tunneling through potential well, and electron hopping via Coulomb-blockade network. Stochastic resonance was observed in Cytochrome c/DNA network.

Video-rate imaging of various types of biological tissue is reported using stimulated Raman scattering microscopy. The label-free scheme offers molecular specificity and frame-by-frame wavelength tunability allowing the creation of 2D and 3D images of samples showing different constituents.

RATIONALE Ambient sampling and ionization techniques have been attracting attention in imaging mass spectrometry because they offer the advantage of rapid testing. We have developed a method which exploits the fluid motion of charged solvents for both local sampling and ionization with a single vibrating capillary probe. METHODS The capillary probe was used to supply solvents in order to form a liquid bridge between the probe and a sample surface. A bias voltage was applied to the solvents to generate electrospray ionization (ESI). The probe was also vibrated by either an ultrasonic transducer fixed at the back of the sample (contact-mode) or spontaneous vibration of probe itself (tapping-mode). The ions generated by ESI were detected by a triple quadrupole mass spectrometer. RESULTS Sampling of the specimens at the liquid bridge and ESI of the dissolved solutions both occurred around the probe apex. The sampling and ionization co-existed in contact-mode, while they were explicitly separated in the tapping-mode. The one-dimensional mapping of solid samples such as protein films and tissue sections was demonstrated. The results indicated that there was little cross-contamination during the operation. CONCLUSIONS The method, named scanning probe electrospray ionization (SPESI), promises to be a simple and unique approach toward direct sampling and ionization methodology.

Correction for ‘Imaging mass spectrometry of a mouse brain by tapping-mode scanning probe electrospray ionization’ by Yoichi Otsuka et al., Analyst, 2014, 139, 2336–2341.

Control of interfaces and boundaries of organic electronic materials are important issues in device applications. Methods to determine electrical transport in such regions on the nanometre-scale are limited, however. We developed top-contact nano-gap electrodes and point-contact current-imaging atomic force microscopy (PCI-AFM) to measure nanometre-scale electrical conduction of organic thin films with reduced damage at metal/organic interfaces. Using these nano-scale methods, in-plane space-charge limited conduction is observed for single-phase monoclinic lead phthalocyanine (PbPc) thin films at high electric field. Apparent film resistivity at low voltage is two orders of magnitude lower than that measured by conventional micro-scale methods. Nanometre-scale spatially-resolved current-analysis of single-domain monoclinic PbPc crystal reveals non-linear distance-resistance characteristics, resulting in a low distance-differential resistance of 10 Ωm. The technologies used here allow us to find intrinsic electrical properties of organic electronic materials and to clarify the influence of interfaces and boundaries, forming the basis of nano-scale organic electronics.

Multinuclear complexes consisting of metal ions and a bis(terpyridyl) ligand were covalently bound to carbon substrates. The bonding of the complexes is initiated by the bonding of phenylterpyridine (PT) on the substrates using its in-situ-generated diazonium derivative, followed by stepwise coordination of the metal ions and the ligand on it. The bonding of the PT and the formation of the multinuclear complexes were confirmed by XPS, AFM, and CV measurements. The heterogeneous rate constant (k) at the Co complex-substrate interface was evaluated by chronoamperometry (CA). The estimated high k = (2.9-3.6) x 10(3) s(-1)) would be attributed to the C-C bond at the interface without interrupting the conjugation. These multinuclear complexes bound to the carbon substrates can facilitate electron transfer from redox species such as enzymes.

Water-soluble non-conjugated thienyl tetraynes (3-6) were synthesized and their DNA cleaving activity was evaluated using electrophoresis, atomic force microscopy (AFM) and Escherichia coli (E. coli) transformation techniques. The amino-functionalized compound 4 was shown to possess an activity to cleave plasmid DNA by both electrophoresis and E. coli transformation techniques. AFM also showed a cleavage of the circular DNA into a linear form with a formation of burst-star-shaped architectures, which were envisaged to be cross-linked DNA oligomers.

Mass spectrometry imaging is an informative approach for the comprehensive analysis of multiple components inside biological specimens. We used novel tapping-mode scanning probe electrospray ionization mass spectrometry method to visualize cancer-related chemical components in the mouse pancreas tissue section at a sampling pitch of 100 µm. Positive ion mode measurements from m/z 100 to 1500 resulted in the visualization of multiple components that are tentatively assigned as polyamines, lipids and proteins. Their signal intensities inside the cancerous and the non-cancerous regions were found to be significantly different by the two-sample t-test.

We have developed a fabrication method for nanogap electrodes without employing photo- or electron-beam lithography to measure the electrical characteristics of nanostructured molecules. This angle-controlled shadow-masking method enables us to construct nanogap electrodes without a wet process after the molecules are positioned on the substrate. The proposed method makes it possible to measure electrical characteristics without structurally deforming or denaturing the molecules due either to the step edge of an electrode or to the organic solvents used in the wet process. The results demonstrate that a gap length between the electrodes of less than 100 nm can be fabricated reproducibly. We have measured the electrical characteristics of lambda DNA (λ-DNA) networks and molecular nanorods made of porphyrin-derivative molecules (TPPS: 5,10,15,20-tetraphenyl-21H,23H-porphyrine tetrasulfonic acid) in which J-aggregates are formed inside. Experimental findings reveal that the electrical conductivity of λ-DNA decreased under a vacuum condition, whereas that of TPPS nanorods decreased under oxygen and nitrogen gas-purged conditions.

DNA is one of the most promising molecules as the scaffold for molecular nanotechnology and nanoelectronics. For realizing the molecular devices constructed with DNA, three kinds of function is required such as (1) circuit and control of the conductivity, (2) switching and (3) storage. We have found that the electrical conducting properties of the DNA networks are strongly depended on the doping condition. Photo-switching (current enhancement with shining the light) and magnetoresistance effect are observed in the dye-modified DNA and Co ions doped DNA, respectively. Furthermore, DNA network pattern can be patterned on the Si/SiO 2 surface. These results have significant implications for the application of DNA in electronic devices and in DNA-based electrochemical biosensors.

A new method for simultaneous measurement of topographic images and current-voltage (I-V) characteristics, based on atomic force microscopy (AFM), has been demonstrated with nano-scale resolution. Point-contact current-imaging atomic force microscopy (PCI-AFM) was developed to solve the incompatibility of electrically stable contact with nano-scale resolution in conductive probe AFM. We herein describe the detail of the PCI-AFM apparatus. Furthermore, the apparatus has been evaluated by the measurement of I-V characteristics of single-walled carbon nanotubes and deoxyribonucleic acid indicating high performance of PCI-AFM.

We have studied the electrical conductivity of DNA film using nanogap electrodes. Current–voltage measurements and alternating current measurements were performed for analysis of conductivity. The electrical conductivity of the DNA films of poly(dG)poly(dC) are found to depend strongly on the humidity. The resistance of poly(dG)poly(dC) decreases dramatically with increasing relative humidity. The contact resistance between DNA film and Au electrodes is also examined by the conventional four-probe technique.

We investigated the electrical properties of a two-dimensional (2D) network consisting of multiple Au nanoparticles (AuNPs) and self-doped polyaniline sulfonate (SPAN). Nonlinear current–voltage (I–V) characteristics with wide variations were observed in the networks. The temperature dependence of the I–V characteristics exhibited a short localization length, suggesting conjugated electronic properties of the AuNP–SPAN network. This result provides a new direction for network-based molecular electronic devices.

Methods for ambient sampling and ionization enable chemical information to be obtained with minimal sample preparation. Also, imaging mass spectrometry (IMS) enables the spatial distribution of multiple components to be determined by a single measurement. Here, we report an improved method of tapping-mode scanning probe electrospray ionization (t-SPESI) for ambient sampling and ionization in which probe oscillation is stabilized by using a piezo actuator. We demonstrate negative-mode IMS of a mouse coronal brain section and show that, compared with desorption electrospray ionization, t-SPESI provides unique features in the mass spectra: signal enhancement of fatty acid and lipids, and formation of multivalent ions tentatively assigned to gangliosides. These results would indicate the capability for the generation of multiple types of ions with t-SPESI.

We recently established a high-speed, label-free, spectral imaging method based on stimulated Raman scattering (SRS). This method enables examination of cellular features within relatively short periods, thus enabling new imaging applications in pathology. Previously, we reported on label-free visualization of mouse tissue using SRS spectral microscopy combined with multivariate image analysis, but the feasibility of applying this approach to diseased tissues with diverse morphology and irregular chemical species has not been examined. We, therefore, assessed acetaminophen-induced liver injury to evaluate the potential use of Raman spectral microscopy for visualizing histopathologic specimens. Acetaminophen-overdosed mouse liver was prepared and the pathologic changes including centrilobular necrosis were confirmed. Multi-colored images were reconstructed through principal component analysis (PCA) of a multi-band SRS dataset, which provided rich information compared with a monochrome single-band SRS dataset. A wide view of the multi-colored principal component (PC) images showed the distribution of cellular constituents, which was similar to that observed by fat staining. In addition, different types of cells in liver parenchyma were also demonstrated. In conclusion, the combination of SRS spectral microscopy and PCA has the potential to reveal both the morphological and chemical features of specimens and therefore has potential utility in diagnostic pathology.

We previously reported the combination of the high-speed stimulated Raman scattering (SRS) microscope and the multivariate analysis (principal component analysis and independent component analysis) for the tissue imaging. The results indicated the visualization of tissue components without chemical staining. Here, we report the multi-area observation of the tumor-grafted mouse tissue based on the same approach. The tumor-grafted mouse (balb/cAcJ nu/nu) was prepared by injection of human pancreatic carcinoma cell line (SUIT-2) into the tail of pancreas. Both of the pancreas cancer and the liver metastasis were harvested and fixed in formalin. Tissues were cryo-sectioned with a thickness of 100 μm and observed. The multispectral images (130 μm square, 500 x 500 pixels) of C-H vibration range from 2800 to 3100cm-1 (91 different Raman shift images) were obtained at a frame rate of 30 frames/sec. The data acquisition both of pancreas and liver were continued for the 48 adjacent areas for the observation both of cancerous and non-cancerous region, respectively. All the datasets were combined to analyze for multivariate analysis. We propose a protocol for drastic data reduction, which we found to give reproducible results and allows fast calculation of ICA. The independent component images indicated the different shapes and compositions between the cancerous region and the non-cancerous region.

Stimulated Raman scattering (SRS) microscopy enables us to observe biological specimens without chemical labeling because of the higher sensitivity and lower background signal compared to spontaneous Raman microscope [1-3].

Conductance of bundled single-walled carbon nanotubes (b-SWCNTs) are measured by point-contact current-imaging atomic force microscopy (PCI–AFM). Simultaneous mapping of the topographic information and current through SWCNTs enable us to investigate the relationship between structure and conductance. Variation in resistance of a b-SWCNT indicates that the resistance between SWCNTs was higher than 107 Ω with strong voltage dependence. Because PCI–AFM measurement can obtain vertical conductance information, this approach appears to be a powerful technique for characterization of nanoscale electronic devices.

A new atomic force microscopy (AFM) technique, called point-contact current-imaging AFM (PCI-AFM)-which combines tapping mode (for mapping topographic image) and point-contact operation (for measuring current?voltage characteristics)-has been developed. This new AFM technique can simultaneously map high-resolution topographic image and measure spatially resolved I?V characteristics of materials (placed on an insulative substrate and connected to a gold electrode) on the nanoscale. The high performance of the PCI-AFM system was evaluated in experiments on single-walled carbon nanotubes (SWNTs).

Using oxygen adsorption experiments on poly (dG)-poly (dC) DNA molecules, we found that their conductance can be easily controlled by several orders of magnitudes using oxygen hole doping, which is a characteristic behavior of a p-type semiconductor. It also suggests that the conductance of the DNA under doping results from charge carrier transport, not from an ionic conduction. On the other hand, we will also show that the poly (dA)-poly (dT) DNA molecules behave as an n-type semiconductor. This letter demonstrates that the concentration and the type of carriers in the DNA molecules could be controlled using proper doping methods.

Mass spectrometry imaging (MSI) with ambient sampling and ionization can rapidly and easily capture the distribution of chemical components in a solid sample. Because the spatial resolution of MSI is limited by the size of the sampling area, reducing sampling size is an important goal for high resolution MSI. Here, we report the first use of a nanopipette for sampling and ionization by tapping-mode scanning probe electrospray ionization (t-SPESI). The spot size of the sampling area of a dye molecular film on a glass substrate was decreased to 6 μm on average by using a nanopipette. On the other hand, ionization efficiency increased with decreasing solvent flow rate. Our results indicate the compatibility between a reduced sampling area and the ionization efficiency using a nanopipette. MSI of micropatterns of ink on a glass and a polymer substrate were also demonstrated.

[1] The total electron content (TEC) obtained from GPS signals is used to study ionospheric dynamics over Japan during geomagnetically disturbed conditions. The numerous TEC measurements are averaged in cells with a size 1.5° × 1.5° geographic scale and formatted as time series within the years 2000–2002. To extract the storm time changes of TEC, the diurnal and 27-day periodicities are subsequently removed. Diurnal variations are removed by replacing absolute TEC values in each cell with their relative deviations (RTEC) from medians. The hourly RTEC values from all cells within the central 4°-wide band over Japan area are then approximated by a plane surface. This surface is represented by two parameters: its value at the center (rt) and the slope (b) along the main axis, taken as constants of the linear regression. The 27-day periodicity was approximated by Fourier waves with main period of 640 hours and two harmonics separately for rt and b and subtracted from them. The analysis of rt and b behavior during a number of geomagnetic storms allowed us to reveal several repeatable features of average TEC behavior. It was found that TEC behavior during the storms is similar to that of foF2 at the F region and was local time–dependent. A marked poleward expansion of the equatorial ionosphere (crest region) at the end of recovery phase is persistently observed feature, produced probably by intensified eastward zonal winds. Such an expansion of equatorial ionosphere is observed also during isolated substorms, outside main geomagnetic storms. An oscillation-like change of positive and negative disturbances with period of 24 hours is observed during a 4-day period, following a moderate storm. In the absence of geomagnetic activity driver that effect is probably caused by the alternative expansion and contraction of equatorial ionosphere.

We have refined the measurement conditions of point-contact current imaging microscopy (PCI-AFM) to measure the electric properties along the long axes of one-dimensional structures. Using this refinement, the current image of the PCI-AFM can be used to distinguish individual single-walled carbon nanotubes in a bundled structure. The PCI-AFM will thus help further developments in nanoscience for conduction measurements in one-dimensional structures.

We measured the electrical conductivity of a DNA network as a spatially-resolved current-image using point-contact current imaging atomic force microscopy (PCI-AFM) under various humidity conditions. The simultaneous observation of topography and current image by PCI-AFM can provide information pertaining to the electrical properties of biological and∕or soft materials in the nano-scale range. Under dry condition (0% humidity), no difference was observed for the electrical current both of the DNA network and mica surface, whereas the electrical current along the DNA network was larger than that of the mica surface by 20pA at a bias voltage of 5V under high humidity conditions of 60%.

To investigate the role of renal vasoactive substances in the pathogenesis of essential hypertension, urinary prostaglandin E excretion, urinary kallikrein excretion, plasma renin activity, plasma aldosterone concentration and urinary Na excretion were measured in normal subjects and patients with essential hypertension after stimulation of the renin—angiotensin—aldosterone system by the intravenous injection of frusemide or a low Na diet; after the inhibition of renin—angiotensin—aldosterone by an angiotensin II antagonist and after the inhibition of renal prostaglandin E synthesis by indomethacin. The urinary excretions of prostaglandin E and kallikrein, plasma renin activity and plasma aldosterone concentration increased after frusemide administration. The urinary excretion of kallikrein increased after frusemide or a low Na diet but decreased after the angiotensin II antagonist and indomethacin during Na depletion. Changes in urinary kallikrein excretion paralleled those in the renin—angiotensin—aldosterone system after various stimuli. The urinary excretion of prostaglandin E increased after frusemide. However, a dissociation between the urinary excretions of prostaglandin E and kallikrein was found during the low Na diet: the former decreased and the latter increased. The urinary excretion of prostaglandin E was closely related to urinary Na output after various stimuli. Basal levels of urinary prostaglandin E and kallikrein excretion were lower in essential hypertension than in normal subjects. The release of renal prostaglandin E and kallikrein after frusemide was also suppressed in essential hypertension compared with that in normal subjects. The data indicate that renal kallikrein—kinin and renin—angiotensin—aldosterone may interact in a dynamic fashion to maintain blood pressure, that renal prostaglandin E may be involved in renal Na handling and that the suppression of renal kallikrein—kinin and prostaglandin E in essential hypertension may be an etiological factor in essential hypertension.