Properties of the voltage-dependent Ca²⁺ current in porcine sino-atrial node cells

Abstract

L-type Ca²⁺ channels play a crucial role in the contraction and the spontaneous activity of the heart. It has been reported that in sinoatrial node cells the L-type Ca²⁺ channels are derived from not only α1C(Cav1.2) but also α1D (Cav1.3). In this study we have investigated the molecular and electrophysiological properties of L-type Ca²⁺ channels in porcine sinoatrial node cells, in comparison to those of ventricular cells. In the patch clamp analysis, the L-type Ca²⁺ current in sinoatrial node cells was activated at more negative potential range than ventricular cells, peaking at 0 mV. Furthermore, the L-type Ca²⁺ current showed a retarded inactivation with a sustained component between -30 and +30 mV in sinoatrial node cells. Western blot analysis revealed the existence of α1D in sinoatrial node but failed to detect it in ventricles. On the other hand, α1C, which was predominant in ventricles, was only detectable in sinoatrial node. Dihydropyridine binding was examined and showed a K_D value of approximately 0.2 nM in both sinoatrial node and ventricles. The results indicate that a1D plays a major role as the L-type Ca²⁺ current in sinoatrial node cells, and may account for the different kinetics of L-type Ca²⁺ current between sinoatrial node and ventricular cells. [Jpn J Physiol 54 Suppl:S127 (2004)]