Intracellular Ca 2+- and PKC-dependent upregulation of T-type Ca 2+ channels in LPC-stimulated cardiomyocytes

Abstract

Lysophosphatidylcholine (LPC) accumulation in intracellular and/or interstitial space in cardiomyocytes may underlie as a mechanism for tachycardia and various arrhythmias during cardiac ischemia, which is usually accompanied by elevation of intracellular Ca 2+ concentration ([Ca 2+] i). The present study was therefore designed to investigate possible mechanisms responsible for [Ca 2+] i elevation by LPC focusing on T-type Ca 2+ channel current (I Ca.T). LPC as well as phorbol 12-myristate 13-acetate (PMA) significantly accelerated the beating rates of neonatal rat cardiomyocytes. Augmentation of I Ca.T by LPC was dependent on the intracellular Ca 2+ concentration: an increase of I Ca.T was significantly larger in high [Ca 2+] i condition (pCa = 7) than those in low [Ca 2+] i condition (pCa = 11). In heterologous expression system by use of human cardiac Ca V3.1 and Ca V3.2 channels expressed in HEK293 cells, LPC augmented Ca V3.2 channel current (I Cav3.2) in a concentration-dependent manner but not Ca V3.1 channel current (I Cav3.1). Augmentation of I Cav3.2 by LPC was highly [Ca 2+] i dependent: I Cav3.2 was unchanged when pCa was 11 but was markedly increased when [Ca 2+] i was higher than 10 −10 M (pCa ≤ 10) by LPC application (10–50 μM). A specific inhibitor of protein kinase Cα (Ro-32-0432) attenuated the increase of I Cav3.2 by LPC. LPC stimulates I Ca.T in a [Ca 2+] i-dependent manner via PKCα activation, which may play a role in triggering arrhythmias in pathophysiological conditions of the heart.