Search

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]

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]