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Background: Resveratrol, a phytoalexin found in grapes and red wine, exhibits diverse pharmacological activities. However, relatively little is known about whether resveratrol modulates the ion channels in cortical neurons. The large-conductance calcium-activated potassium channels (BKCa) and voltage-gated sodium channels were expressed in cortical neurons and play important roles in regulation of neuronal excitability. The present study aimed to determine the effects of resveratrol on BKCa currents and voltage-gated sodium currents in cortical neurons. Results: Resveratrol concentration-dependently increased the current amplitude and the opening activity of BKCa channels, but suppressed the amplitude of voltage-gated sodium currents. Similar to the BKCa channel opener NS1619, resveratrol decreased the firing rate of action potentials. In addition, the enhancing effects of BKCa channel blockers tetraethylammonium (TEA) and paxilline on action potential firing were sensitive to resveratrol. Our results indicated that the attenuation of action potential firing rate by resveratrol might be mediated through opening the BKCa channels and closing the voltage-gated sodium channels. Conclusions: As BKCa channels and sodium channels are critical molecular determinants for seizure generation, our findings suggest that regulation of these two channels in cortical neurons probably makes a considerable contribution to the antiseizure activity of resveratrol. [ABSTRACT FROM AUTHOR]

Di-8-ANEPPS (4-{2-[6-(dibutylamino)-2-naphthalenyl]-ethenyl}-1-(3-sulfopropyl)pyridinium inner salt) has been used as a fast-response voltage-sensitive styrylpyridinium probe. However, little is known regarding the mechanism of di-8-ANEPPS actions on ion currents. In this study, the effects of this dye on ion currents were investigated in pituitary GH3 cells. In whole-cell configuration, di-8-ANEPPS (10 μM) reversibly increased the amplitude of Ca2+-activated K+ current. In inside-out configuration, di-8-ANEPPS (10 μM) applied to the intracellular surface of the membrane caused no change in single-channel conductance; however, it did enhance the activity of large-conductance Ca2+-activated K+ (BKCa) channels with an EC50 value of 7.5 μM. This compound caused a left shift in the activation curve of BKCa channels with no change in the gating charge of these channels. A decrease in mean closed time of the channels was seen in the presence of this dye. In the cell-attached mode, di-8-ANEPPS applied on the extracellular side of the membrane also activated BKCa channels. However, neither voltage-gated K+ nor ether-à-go-go-related gene ( erg)-mediated K+ currents in GH3 cells were affected by di-8-APPNES. Under current-clamp configuration, di-8-ANEPPS (10 μM) decreased the firing of action potentials in GH3 cells. In pancreatic βTC-6 cells, di-8-APPNES (10 μM) also increased BKCa-channel activity. Taken together, this study suggests that during the exposure to di-8-ANEPPS, the stimulatory effects on BKCa channels could be one of potential mechanisms through which it may affect cell excitability. [ABSTRACT FROM AUTHOR]

The effects of rottlerin, a known inhibitor of protein kinase C-δ activation, on ion currents were investigated in pituitary tumor (GH3) cells. Rottlerin (0.3–100 µM) increased the amplitude of Ca2+-activated K+ current (IK(Ca)) in a concentration-dependent manner with an EC50 value of 1.7 µM. In intracellular perfusion with rottlerin (1 µM) or staurosporine (10 µM), phorbol 12-myristate 13-acetate-induced inhibition of IK(Ca) in these cells was abolished. In cell-attached mode, rottlerin applied on the extracellular side of the membrane caused activation of large-conductance Ca2+-activated K+ (BKCa) channels, and a further application of BAPTA-AM (10 µM) to the bath had no effect on rottlerin-stimulated channel activity. When cells were exposed to rottlerin, the activation curve of these channels was shifted to less positive potential with no change in the slope factor. Rottlerin increased BKCa-channel activity in outside-out patches. Its change in kinetic behavior of BKCa channels is primarily due to an increase in mean open time. With the aid of minimal kinetic scheme, a quantitative description of rottlerin stimulation on BKCa channels in GH3 cells was also provided. Under current-clamp configuration, rottlerin (1 µM) decreased the firing of action potentials. IK(Ca) elicited by simulated action potential waveforms was enhanced by this compound. In human cortical HCN-1A cells, rottlerin (1 µM) could also interact with the BKCa channel to stimulate IK(Ca). Therefore, rottlerin may directly activate BKCa channels in neurons or endocrine cells. J. Cell. Physiol. 210: 655–666, 2007. © 2006 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Cardiac fibroblasts are involved in the maintenance of myocardial tissue structure. However, little is known about ion currents in human cardiac fibroblasts. It has been recently reported that cardiac fibroblasts can interact electrically with cardiomyocytes through gap junctions. Ca2+-activated K+ currents ( I K[Ca]) of cultured human cardiac fibroblasts were characterized in this study. In whole-cell configuration, depolarizing pulses evoked I K(Ca) in an outward rectification in these cells, the amplitude of which was suppressed by paxilline (1 μ M) or iberiotoxin (200 n M). A large-conductance, Ca2+-activated K+ (BKCa) channel with single-channel conductance of 162 ± 8 pS was also observed in human cardiac fibroblasts. Western blot analysis revealed the presence of α-subunit of BKCa channels. The dynamic Luo-Rudy model was applied to predict cell behavior during direct electrical coupling of cardiomyocytes and cardiac fibroblasts. In the simulation, electrically coupled cardiac fibroblasts also exhibited action potential; however, they were electrically inert with no gap-junctional coupling. The simulation predicts that changes in gap junction coupling conductance can influence the configuration of cardiac action potential and cardiomyocyte excitability. I k(Ca) can be elicited by simulated action potential waveforms of cardiac fibroblasts when they are electrically coupled to cardiomyocytes. This study demonstrates that a BKCa channel is functionally expressed in human cardiac fibroblasts. The activity of these BKCa channels present in human cardiac fibroblasts may contribute to the functional activities of heart cells through transfer of electrical signals between these two cell types. [ABSTRACT FROM AUTHOR]

Aconitine (ACO), a highly toxic diterpenoid alkaloid, is recognized to have effects on cardiac voltage–gated Na+ channels. However, it remains unknown whether it has any effects on K+ currents. The effects of ACO on ion currents in differentiated clonal cardiac (H9c2) cells and in cultured neonatal rat ventricular myocytes were investigated in this study. In H9c2 cells, ACO suppressed ultrarapid-delayed rectifier K+ current (IKur) in a time- and concentration-dependent fashion. The IC50 value for ACO-induced inhibition of IKur was 1.4μM. ACO could accelerate the inactivation of IKur with no change in the activation time constant of this current. Steady-state inactivation curve of IKur during exposure to ACO could be demonstrated. Recovery from block by ACO was fitted by a single-exponential function. The inhibition of IKur by ACO could still be observed in H9c2 cells preincubated with ruthenium red (30μM). Intracellular dialysis with ACO (30μM) had no effects on IKur. IKur elicited by simulated action potential (AP) waveforms was sensitive to block by ACO. Single-cell Ca2+ imaging revealed that ACO (10μM) alone did not affect intracellular Ca2+ in H9c2 cells. In cultured neonatal rat ventricular myocytes, ACO also blocked IKur and prolonged AP along with appearance of early afterdepolarizations. Multielectrode recordings on neonatal rat ventricular tissues also suggested that ACO-induced electrocardiographic changes could be associated with inhibition of IKur. This study provides the evidence that ACO can produce a depressant action on IKur in cardiac myocytes. [ABSTRACT FROM AUTHOR]

Margatoxin and quercetin can have an immunomodulatory role in T lymphocytes. It remains to be further investigated how these substances affect ion currents in T lymphocytes. With the aid of whole-cell patch-clamp technique, we assessed the effect of margatoxin on ion currents in Jurkat T lymphocytes. Whole-cell K+ outward currents (IK) with an outward rectification found in these cells were identified as the Kv1.3 current. We also found out that unlike iberiotoxin or charybdotoxin, margatoxin could be effective in blocking the amplitude of IK in a concentration-dependent manner, although its IC50 value was slightly higher as compared with previous reports. Similar results were also obtained in the presence of agitoxin. Unlike verapamil and quercetin, margatoxin block IK in a time-independent manner. No effect of margatoxin on L-type Ca2+ current in Jurkat T lymphocytes was found, although quercetin (10 µM) enhanced it. In addition, no effects of this toxin (up to 10 µM) on the activity of large-conductance Ca2+-activated K+ channels in pituitary GH3 cells and in human skeletal muscle cells were demonstrated. In intracellular Ca2+ measurements, pretreatment of Fura-2-loaded Jurkat T lymphocytes with margatoxin was also found to attenuate the ionomycin-induced increase in intracellular Ca2+. Our results indicate that margatoxin and quercetin may differentially influence ion currents in T lymphocytes. [ABSTRACT FROM AUTHOR]

The agonists selective for estrogen receptor (ER)-α propylpyrazole-triol, PPT) and ER-β diarylpropionitrile, DPN) can bind to the ER-α and ER-β receptors which may be localized to the plasma membrane. It is unclear whether DPN or PPT influence ion channels linked to non-genomic mechanism. We tested the hypothesis that DPN or PPT directly stimulates the large-conductance Ca2+-activated K+ (BKCa) channels in human cardiac fibroblasts (HCFs). In whole-cell configuration, depolarizing pulses evoked K+ outward currents in an outward rectification in HCFs, the amplitude of which was increased by DPN or PPT. Applied to the intracellular surface of excised patches, PPT or DPN enhanced BKCa-channel activity with no change in single-channel conductance. DPN and PPT increased BKCa-channel activity with an EC50 value of 2.3 and 2.6 µM, respectively. The mean closed time of these channels measured during the exposure to DPN or PPT was reduced with no change in the gating charge of the channels. Intracellular Ca2+ was not altered in the presence of these two compounds. RT-PCR study also revealed that no change in the transcriptional level of the BKCa channel α-subunit was observed in treatment with DPN or PPT. Our data suggest that PPT- and DPN-mediated activation of BKCa channels reveal novel pharmacological properties attributable to the activity of these channels. [ABSTRACT FROM AUTHOR]

Ion currents functionally expressed in undifferentiated and differentiated human skeletal muscle cells (HSkMCs), were characterized in this study. A human ion channel and transporter gene array (SuperArrayTM®) was also probed to compare changes in ion channel expression between undifferentiated and differentiated cells. During one-week culture in differentiating medium, HSkMCs were found to contract spontaneously. These cells underwent differentiation to exhibit actin and myosin myofilaments. Western blotting revealed increased expression in p27 after differentiation. In patch-clamp studies, after being differentiated, the density of inwardly rectifying K+ current was reduced and that of voltage-gated Na+ current and skeletal L-type Ca2+ current was significantly increased, while the density of voltage-gated K+ current and the activity of large-conductance Ca2+-activated K+ channels remained unaltered. Our microarray results showed that a group of ion channel genes were expressed in HSkMCs. The messages for KCNJx was relatively reduced in differentiated HSkMCs, while those of KCNAx and KCNHx was unaltered after differentiation. Taken together, the results indicate that spontaneous beating in differentiated HSkMCs is primarily related to the reduction of KCNJx expression. [ABSTRACT FROM AUTHOR]