Morishima Masaki, Tahara Shintaro, Wang Yan, Ono Katsushige
Department of Pathophysiology, Oita University School of Medicine, Oita 879-5593, Japan.
Department of Food Science and Nutrition, Kindai University Faculty of Agriculture, Nara 631-8505, Japan.
Membranes (Basel). 2021 Mar 25;11(4):234. doi: 10.3390/membranes11040234.
Oxytocin (OT) and its receptor (OTR) are expressed in the heart and are involved in the physiological cardiovascular functional system. Although it is known that OT/OTR signaling is cardioprotective by reducing the inflammatory response and improving cardiovascular function, the role of OT in the cardiac electrical excitation modulation has not been clarified. This study investigates the molecular mechanism of the action of OT on cardiomyocyte membrane excitation focusing on the L-type Ca channel. Our methodology uses molecular biological methods and a patch-clamp technique on rat cardiomyocytes with OT, combined with several signal inhibitors and/or activators. Our results show that long-term treatment of OT significantly decreases the expression of Cav1.2 mRNA, and reduces the L-type Ca channel current (I) in cardiomyocytes. OT downregulates the phosphorylated component of a transcription factor adenosine-3',5'-cyclic monophosphate (cAMP) response element binding protein (CREB), whose action is blocked by OTR antagonist and pertussis toxin, a specific inhibitor of the inhibitory GTP-binding regulators of adenylate cyclase, Gi. On the other hand, the upregulation of Cav1.2 mRNA expression by isoproterenol is halted by OT. Furthermore, inhibition of phospholipase C (PLC) was without effect on the OT action to downregulate Cav1.2 mRNA-which suggests a signal pathway of Gi/protein kinase A (PKA)/CREB mediated by OT/OTR. These findings indicate novel signaling pathways of OT contributing to a downregulation of the Cav1.2-L-type Ca channel in cardiomyocytes.
催产素（OT）及其受体（OTR）在心脏中表达，并参与生理心血管功能系统。尽管已知OT/OTR信号通过减少炎症反应和改善心血管功能而具有心脏保护作用，但OT在心脏电兴奋调节中的作用尚未阐明。本研究以L型钙通道为重点，研究OT对心肌细胞膜兴奋作用的分子机制。我们的方法采用分子生物学方法和对大鼠心肌细胞施加OT的膜片钳技术，并结合几种信号抑制剂和/或激活剂。我们的结果表明，长期使用OT可显著降低Cav1.2 mRNA的表达，并降低心肌细胞中的L型钙通道电流（I）。OT下调转录因子腺苷-3',5'-环磷酸（cAMP）反应元件结合蛋白（CREB）的磷酸化成分，其作用被OTR拮抗剂和百日咳毒素阻断，百日咳毒素是腺苷酸环化酶抑制性GTP结合调节因子Gi的特异性抑制剂。另一方面，异丙肾上腺素引起的Cav1.2 mRNA表达上调被OT阻断。此外，抑制磷脂酶C（PLC）对OT下调Cav1.2 mRNA的作用没有影响——这表明存在由OT/OTR介导的Gi/蛋白激酶A（PKA）/CREB信号通路。这些发现表明了OT导致心肌细胞中Cav1.2-L型钙通道下调的新信号通路。
