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In the system of MnTa2O6-FeTa2O6, Mn2+ was substituted up to about 80 at% for Fe2+ in trirutile-type FeTa2O6, and Fe2+ was substituted up to 13 at% for Mn2+ in MnTa2O6. In the MnNb2O6-MnTa2O6 system, all solid solutions had the columbite-typ structure. Single crystals of tantalite solid solutions having the composition of FexMn1−xTa2O6 (0.00 ≦ x ≦1.00) and Mn(TayNb1-y)2O6 (0.00 ≦ y ≦ 1.00) were grown by the floating zone method using an infrared heating furnace unde controlled atmosphere of oxygen pressure. Trirutile-type single crystals of FexMn1-xTa2O6 with 0.40 ≦ x ≦ 1.00 and col type single crystals of Mn(TayNb1-y)2O6 with 0.00 ≦ y ≦ 0.50 were obtained. The crystals were 5 mm in diameter by about length, and were crack-free, metallic lustrous and black.

In circular muscles of the canine stomach, diltiazem (greater than 3 X 10(-6)M) depolarized and nicardipine (greater than 10(-6)M) hyperpolarized the membrane. Diltiazem (greater than 5 X 10(-6)M) or nicardipine (greater than 3 X 10(-7M) inhibited the plateau potential of spontaneously generated or electrically evoked action potential. In Na-deficient solution (between 137 and 30 mM Na), diltiazem and nicardipine selectively inhibited the plateau potential. In Na- (15 mM Na) or Ca-deficient (0.25 mM Ca) solution, spontaneously generated action potential ceased, and only graded responses were evoked by electrical stimulation. These graded responses were inhibited by diltiazem (greater than 5 X 10(-6)M) or nicardipine (greater than 3 X 10(-7)M). The ionic contribution for generation of action potential in this muscle cell was discussed in relation to actions of Ca antagonists.

We found a new type of Ca2+-dependent K+ channel in smooth muscle cell membranes of single cells of the rabbit portal vein. A slope conductance of the current was 180 pS when 142 mM K+ solution was exposed to both sides of the membrane (this channel was named the KM channel, in comparison to the known KL and KS channels from the same membrane patch; Inoue et al. 1985). This KM channel was less sensitive to the cytoplasmic Ca2+ concentration, [Ca2+]i, but was sensitive to the extracellular Ca2+, [Ca2+]o, e.g. in the outside-out membrane patch, lowering the [Ca2+]o in the bath markedly reduced the open probability of this channel, and also in cell-attached configuration, lowering of the [Ca2+]o using the internally perfused patch clamp electrode device reduced the opening of KM channel. TEA+ (1–10 mM) reduced the amplitude of the elementary current through the KM channel applied from each side of the membrane, but this agent inhibited the KM channel to a greater extent when applied to the inner than to the outer surface of the membrane. Furthermore, this KM channel had a weak voltage dependency, and the open probability of the channel remained much the same within a wide range of potential (from −60 mV to +60 mV). Whereas most Ca2+-dependent K+ channels are regulated mainly by [Ca2+]i and possess a voltage dependency, these properties of the KM channel differed from other Ca2+-dependent K+ channels. The elucidation of this KM channel should facilitate explanations of the actions of external Ca2+ or TEA+ on the membrane potential, in the smooth muscles of the rabbit portal vein.

The effects of intracellular perfusion of inositol 1,4,5-trisphosphate (InsP3) or inositol 1,3,4,5-tetrakisphosphate (InsP4) on electrical responses of smooth muscle cell membranes of the rabbit portal vein were studied using the whole cell voltage clamp technique. Depolarisation to 0 mV from a holding potential of −60 mV, evoked inward Ca (I Ca), transient outward (I TO), oscillatory outward (I OO) and sustained outward (I SO) currents. Generation ofI OO was dependent on the [Ca]o, but it was also generated in 0 mM Ca solution for over 10 min. Form amplitude histograms,I OO was divided into two components. Reduction in [Ca]o inhibited the appearance of but not the amplitudes of bothI OO components. However, the larger component ofI OO was more resistant to a reduction in [Ca]o than the smaller one. InsP3 (10 μM) increased the frequency of bothI OO components to a greater extent than their amplitude, but the larger component was more sensitive to InsP3 than the smaller one. The increase in the occurrence ofI OO induced by InsP3 did not occur following pretreatment with 3 mM caffeine or 1 nM A23187. In normal PSS, InsP3 was evoked by a depolarising pulse positive to −40 mV, whereas following perfusion with InsP3 (10 μM),I OO was evoked at −60 mV. In normal PSS, intracellular perfusion with 10 μM InsP4 changed neither the frequency nor the amplitude ofI OO, and the amplitudes ofI Ca,I TO andI SO were also unchanged. However, in 10 mM Ca solution, 10 μM InsP4 generatedI OO at a membrane potential of −60 mV. It is concluded that InsP3 activatesI OO in smooth muscle cell membranes of the rabbit portal vein by causing an increase in intracellular Ca by facilitating Ca release from the storage sites. In 10 mM Ca solution, InsP4 also accelerates the generation ofI OO, and it is possible that this effect is mediated by inositol 1,3,4-trisphosphate, a metabolite of InsP4 rather than by InsP4 itself.

A sensor for detecting CH 4 in exhaust gases from gasoline engines has been constructed from two Pd | YSZ | Au cells, which are attached to each other with their Pd electrodes in the interior side of the assembly. When the sample gases consisting of CH 4 , O 2 and H 2 O were fed to the sensor element at 750°C, EMF values were generated from the one cell and then compensated by pumping O 2 electrochemically from the other cell. Currents applied to the latter cell linearly increased with CH 4 concentration, but were not influenced by changing O 2 concentration.

Subfamily of human expressed TRPC channels (TRPC3/6/7) are activated by ‘diacylglycerol' (DAG), a phospholipase C (PLC) hydrolyzed product of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] (Hofmann et al., 1999, Nature). In contrary, we have recently reported that the depletion of PI(4,5)P2 by-itself act as a potent negative regulator to all these channels even in the presence of DAG (Imai et al., 2012, J. of Physiol.). Stimulation upon the vasoconstrictile receptors coupled with PLC theoretically causes inseparable bimodal effect to these TRPC channels, i.e. activation and inhibition by DAG production and coincident PI(4,5)P2 reduction or depletion which is corresponding to the strength of PLC activities. Here, to elucidate such self-limiting regulatory function coupled to PI(4,5)P2-DAG signal, we simultaneously measure TRPC6/7 currents in the whole-cell configuration and PI(4,5)P2 dynamics by FRET using PI(4,5)P2 binding PH-domain sensor proteins in the various strength of muscarinic- or vasopressin-receptor stimulation. Our simultaneous detection approach reveals good kinetics correlation between TRPC activation/fast-inactivation and PI(4,5)P2 depletion. Furthermore, a simple self-limiting regulation model wherein experimentally determined PI(4,5)P2 binding constants incorporated aware an emergence of fast recovery of PI(4,5)P2 to produce slow inactivation (plateau phase) of TRPC currents. We find that such model implicated PI(4,5)P2 enhancement can be reproduced after the fast PI(4,5)P2 depletion under the robust agonist stimulation by the local FRET measurement near the channels. Hence, these data indicates that self-limiting regulation coupled to PI(4,5)P2-DAG signal is the pivotal mechanism to understand the receptor-PLC mediated TRPC3/6/7 channels activity.

Calmodulin (CaM) contributes a variety of ion channels gating regulation in response to Ca2+ changes. However, it is still missing the molecular basis of CaM regulation in mammalian TRP channels which contribute to receptor-operated cation (Ca2+ and Na+) currents. To accumulate of Ca2+ and CaM roles in TRP channels, we have firstly characterized the Ca2+ regulation in TRPC6 channel, which is highly expressed in pulmonary and vascular smooth muscle cells. The decay of the receptor-operated cation currents of TRPC6 channels was clearly delayed to EGTA or BAPTA chelation, which suggested the global Ca2+ mechanism. We then examined CaM binding to the C-terminal region of TRPC6 channels by using of Ca2+-dependent FRET system. FRET due to CaM binding to the C-terminal region of TRPC6 channels demonstrated a bell-shape response curve to Ca2+ increments, which was a unique pattern compared to the IQ-domain of voltage-gated Ca and Na channels. And the bell-shape response curve was altered to a simple grow curve by a mutation in either N- or C-globular Ca2+-binding domain (lobe) of CaM. Intriguingly, the mutant in the N-globular domain of CaM delayed the decay of receptor-operated currents of TRPC6 channels, thus the lobe-specific function of CaM appeared in TRP channels. These results indicated that the Ca2+-dependent inactivation of TRPC6 channels can be explain by the bell-shape response curve of CaM binding which curve is probably caused by a conflictive binding between the N- and C-globular domain of CaM to TRPC6 channels. Our results provide a unique molecular basis of CaM to terminate ion channel activity which has critical roles in the down-stream of vasoconstrictors, transmitters and growth factors.