[Regulation of T-type Ca(2+) channel in lysophosphatidylcholine-stimulated cardiomyocytes]

To study the effect of lysophosphatidylcholine (LPC) on T-type calcium channel currents (I(Ca.T)) in cardiomyocytes, and identify the mechanism by which LPC accumulation in intracellular and/or interstitial space may uptake tachycardia and various arrhythmias during cardiac ischemia.

Neonatal rat cardiomyocytes from 1 to 3-day-old Wistar rats and hypertrophied ventricular myocytes from Wistar rats were prepared. Human cardiac T-type calcium channel α1 subunits, Ca(V3.1) and Ca(V3.2), were stably expressed in HEK293 cells. In this study, cardiomyocytes and heterologous expression of human Ca(V3.1) and Ca(V3.2) components were measureed by whole-cell patch clamp to study the up-regulation of I(Ca.T) by LPC.

LPC markedly accelerated the spontaneous beating rates of neonatal rat cardiomyocytes from (42±8) beats/min in control to (64 ±8) beats/min after LPC application for 5 min at the physiological [Ca(2+)](i) concentration (pCa=7.2). In neonatal cardiomyocytes, I(Ca.T) was significantly increased by 10 μmol/L LPC by 21.5% when [Ca(2+)](i) was high (pCa=7). Intracellular Ca(2+)-dependent augmentation of I(Ca.T) by LPC was confirmed not only in neonatal cardiomyocytes but also in adult ventricular myocytes from the hypertrophied hearts. In this experiment, I(Ca.T) was significantly increased by 10 μmol/L LPC by 23.5% when [Ca(2+)](i) was high (pCa=7), although it was unchanged when [Ca(2+)](i) was low (pCa=11), control: (3.8±0.2) pA/pF, n=16; LPC: (3.7±0.4) pA/pF, n=10. LPC exerted no effect on the Ca(V3.1) T-type Ca(2+) channel current (I(Ca(V)3.1)) regardless of the [Ca(2+)](i) concentration at a pCa of 7 or at a pCa of 11. In contrast, LPC up-regulated the Ca(V3.2) T-type Ca(2+) channel current (I(Ca(V)3.2)), which was much larger at a pCa of 7 [LPC=10 μmol/L: (68.8±2.1) pA/pF, n=10; LPC=50 μmol/L: (78.4±4.8) pA/pF, n=9)] than that at a pCa of 11 [(38.5±2.1) pA/pF, n=11].

The present study indicates that LPC up-regulates the cardiac I(Ca.T) in physiological or higher [Ca(2+)](i) concentration, which may accelerate the pathophysiological cardiac automaticity and trigger tachyarrhythmias as novel ischemia-related mechanism.