A new sastained inward current in the cardiac pacemaker cells.

研究了持续内向电流的离子选择性。兔SA结细胞全细胞记录显示，在电位为正至-70 mV时，持续性内向电流被激活，而在电位为正至-40 mV时，L型Ca^<2+>电流被激活。当外界Ca^<2+>浓度降低至0.1 mM时，这种持续性内向电流仍保持完整，L型Ca^<2+>电流被完全抑制。另一方面，耗尽外部Na^+后，持续内向电流消失，而L型Ca^2+电流仍保持在正电位，至-40 mV。用不同的阳离子替代外部Na^+，可改变持续内向电流的幅度，Na^+>Li^+>K^+=Cs^+。家兔房室结细胞也具有持续性内向电流，并显示自发动作电位。这些结果有力地表明，持续的内向电流在驱动舒张期去极化过程中起着重要作用。

The ion selectivity of the sustained inward current was investigated. The whole cell recording from rabbit SA node cells showed activation of the sustained inward current at potentials positive to -70mV,while the activation of the L-type Ca^<2+> current was observed at potentials positive to -40mV.This sustained inward remained intact when the external Ca^<2+> concentration was lowered to 0.1mM,at which the L-type Ca^<2+> current was totally suppressed. On the other hand depletion of the external Na^+ removed the sustained inward current, while the L-type Ca^<2+> current remained at potentials positive to -40mV.The amplitude of the sustained inward current was varied by replacing the external Na^+ with various cations, Na^+>Li^+>K^+=Cs^+.The sustained iward current was also observed in guinea-pig and rat SA node cells. The rabbit AV node cells, showing spontaneous action potentials, also possessed the sustained inward current. These findings stongly suggested that the sustained inward current play an essential role in driving the diastolic depolarization.