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。全细胞记录显示，在-70 mV时激活持续内向电流，而在-40 mV时激活L型钙电流。当外加钙浓度降至0.1 mM时，这种持续内向电流保持不变，此时L型钙电流被完全抑制。外源性Na~(++)的耗竭使持续内向电流消失，而L型钙离子电流维持在-40 mV的正电位。用不同的阳离子Na~+&gt；Li~(++)&gt；K~(++)=Cs~(++)取代外源性Na~(+)，使外源性内向电流的幅度发生变化。显示自发动作电位的兔房室结细胞也具有持续的内向电流。这些发现强烈地表明，持续的内向电流在驱动舒张期去极化中起着重要作用。

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.