Pinacidil, a KATP channel opener, stimulates cardiac Na+/Ca2+ exchanger function through the NO/cGMP/PKG signaling pathway in guinea pig cardiac ventricular myocytes
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Pinacidil, a nonselective ATP-sensitive K+ (KATP) channel opener, has cardioprotective effects for hypertension, ischemia/reperfusion injury, and arrhythmia. This agent abolishes early afterdepolarizations, delayed afterdepolarizations (DADs), and abnormal automaticity in canine cardiac ventricular myocytes. DADs are well known to be caused by the Na+/Ca2+ exchange current (INCX). In this study, we used the whole-cell patch-clamp technique and Fura-2/AM (Ca2+-indicator) method to investigate the effect of pinacidil on INCX in isolated guinea pig cardiac ventricular myocytes. In the patch-clamp study, pinacidil enhanced INCX in a concentration-dependent manner. The half-maximal effective concentration values were 23.5 and 23.0 μM for the Ca2+ entry (outward) and Ca2+ exit (inward) components of INCX, respectively. The pinacidil-induced INCX increase was blocked by L-NAME, a nitric oxide (NO) synthase inhibitor, by ODQ, a soluble guanylate cyclase inhibitor, and by KT5823, a cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG) inhibitor, but not by N-2-mercaptopropyonyl glycine (MPG), a reactive oxygen species (ROS) scavenger. Glibenclamide, a nonselective KATP channel inhibitor, blocked the pinacidil-induced INCX increase, while 5-HD, a selective mitochondria KATP channel inhibitor, did not. In the Fura-2/AM study pinacidil also enhanced intracellular Ca2+ concentration, which was inhibited by L-NAME, ODQ, KT5823, and glibenclamide, but not by MPG and 5-HD. Sildenafil, a phosphodiesterase 5 inhibitor, increased further the pinacidil-induced INCX increase. Sodium nitroprusside, a NO donor, also increased INCX. In conclusion, pinacidil may stimulate cardiac Na+/Ca2+ exchanger (NCX1) by opening plasma membrane KATP channels and activating the NO/cGMP/PKG signaling pathway.
KeywordsPinacidil Nonselective KATP channel opener Na+/Ca2+ exchange current (INCX) Cardiac myocytes Patch-clamp technique
We thank Dr. Junko Kimura and Prof. Yuichi Hattori for helpful and critical comments on the manuscript. This study was supported by Grant-in-Aids for Scientific Research (17 K11047, 16 K09428) from the Japan Society for Promotion of Science.
M.S., Y.M., and Y.W. conceived and designed the experiments. K.I., K.Y., H.P., and M.S. performed the experiments. K.I., K.Y., and Y.W. analyzed the data. K.I. and Y.W. wrote the article. All authors read and approved the manuscript.
Compliance with ethical standards
Conflict of interest
The authors of this manuscript have no conflict of interest to declare.
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