Endothelin-1 inhibition of the ATP-sensitive K+ channel in guinea-pig ventricular cardiomyocytes

Effects of porcine–human endothelin-1 on mechanical as well as electrical activities and on intracellular free Ca2+ levels in the guinea pig taenia coli were compared with those of nifedipine, a voltage-dependent Ca2+ channel blocker. Endothelin-1 (0.1–100 nM) caused a concentration-dependent suppression of spontaneous contractions but did not significantly affect the sustained contraction evoked by 40 mM KCl. However, nifedipine (0.1–100 nM) inhibited both types of contractions in a concentration-dependent manner. In electrophysiological studies, endothelin-1 (30 nM) or nifedipine (30 nM) eliminated spontaneous spike discharges. Endothelin-1 produced hyperpolarization, while nifedipine did not change the resting membrane potential. The endothelin-1 induced suppression of spontaneous contractions was dose-dependently antagonized by apamin (0.01–10 nM), an inhibitor of a small conductance Ca2+-dependent K+ channel, and D-tubocurarine (10–100 μM), an inhibitor of Ca2+-dependent K+ channel, but was unaffected by 4-aminopyridine (0.01–1 mM), an inhibitor of a voltage-dependent K+ channel. In the study with fura 2 excited at 340 nm, endothelin-1 abolished, from the tissue, the fluorescence signals that were coupled with spontaneous contraction. It is suggested that the inhibitory action of endothelin-1 on spontaneous contraction may be caused by hyperpolarization of the membrane that reduces the spontaneous generation of spike discharge coupled normally to an increase in the intracellular free Ca2+ levels in the guinea pig taenia coli. The hyperpolarization may be caused by activating apamin-sensitive Ca2+-dependent K+ channels.Key words: guinea pig taenia coli, endothelin-1, membrane potential, apamin, 4-aminopyridine.

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Direct inhibition by taurine of the ATP-sensitive K+ channel in guinea pig ventricular cardiomyocytes

General Pharmacology The Vascular System ◽

10.1016/0306-3623(95)02068-3 ◽

1996 ◽

Vol 27 (4) ◽

pp. 625-627 ◽

Cited By ~ 16

Author(s):

Hiroyasu Satoh

Keyword(s):

Guinea Pig ◽

K Channel ◽

Direct Inhibition ◽

Ventricular Cardiomyocytes

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Large-conductance voltage- and Ca2+-activated K+ channel regulation by protein kinase C in guinea pig urinary bladder smooth muscle

AJP Cell Physiology ◽

10.1152/ajpcell.00325.2013 ◽

2014 ◽

Vol 306 (5) ◽

pp. C460-C470 ◽

Cited By ~ 18

Author(s):

Kiril L. Hristov ◽

Amy C. Smith ◽

Shankar P. Parajuli ◽

John Malysz ◽

Georgi V. Petkov

Keyword(s):

Smooth Muscle ◽

Membrane Potential ◽

Guinea Pig ◽

Bk Channels ◽

Bk Channel ◽

K Channel ◽

Channel Activity ◽

Open Probability ◽

Channel Regulation ◽

Pkc Activation

Large-conductance voltage- and Ca2+-activated K+ (BK) channels are critical regulators of detrusor smooth muscle (DSM) excitability and contractility. PKC modulates the contraction of DSM and BK channel activity in non-DSM cells; however, the cellular mechanism regulating the PKC-BK channel interaction in DSM remains unknown. We provide a novel mechanistic insight into BK channel regulation by PKC in DSM. We used patch-clamp electrophysiology, live-cell Ca2+ imaging, and functional studies of DSM contractility to elucidate BK channel regulation by PKC at cellular and tissue levels. Voltage-clamp experiments showed that pharmacological activation of PKC with PMA inhibited the spontaneous transient BK currents in native freshly isolated guinea pig DSM cells. Current-clamp recordings revealed that PMA significantly depolarized DSM membrane potential and inhibited the spontaneous transient hyperpolarizations in DSM cells. The PMA inhibitory effects on DSM membrane potential were completely abolished by the selective BK channel inhibitor paxilline. Activation of PKC with PMA did not affect the amplitude of the voltage-step-induced whole cell steady-state BK current or the single BK channel open probability (recorded in cell-attached mode) upon inhibition of all major Ca2+ sources for BK channel activation with thapsigargin, ryanodine, and nifedipine. PKC activation with PMA elevated intracellular Ca2+ levels in DSM cells and increased spontaneous phasic and nerve-evoked contractions of DSM isolated strips. Our results support the concept that PKC activation leads to a reduction of BK channel activity in DSM via a Ca2+-dependent mechanism, thus increasing DSM contractility.

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