A new sastained inward current in the cardiac pacemaker cells.

研究了持续向内电流对离子的选择性。兔窦房结细胞全细胞记录显示，在正-70mV电位范围内，持续向内电流被激活，而在正-40mV电位范围内，l型Ca^<2+>电流被激活。当外部Ca^<2+>浓度降至0.1mM时，l型Ca^<2+>电流被完全抑制，这种持续向内的电流保持不变。另一方面，外部Na^+的耗尽消除了持续向内电流，而l型Ca^<2+>电流保持在正电位至-40mV。持续向内电流的振幅是通过用不同的阳离子代替外部Na^+来改变的，Na^+>Li^+>K^+=Cs^+。在豚鼠和大鼠窦房结细胞中也观察到持续向流。兔房室结细胞表现自发动作电位，也具有持续向内电流。这些发现强烈提示持续向内电流在驱动舒张期去极化中起重要作用。

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.