Koketsu K, Nishi S
J Gen Physiol. 1969 May;53(5):608-23. doi: 10.1085/jgp.53.5.608.
Bullfrog sympathetic ganglion cells were capable of producing action potentials (Ca spikes) in an isotonic (84 mM) CaCl2 solution. The peak level of Ca spikes showed an approximately 30 mv increase with a 10-fold increase in the Ca concentration. Na as well as Ca ions were capable of acting as charge carriers during the production of action potentials in a solution containing relatively high Ca and relatively low Na ions. A decrease in the external Ca concentration depressed the maximum rate of rise at a fixed resting potential level, and increased the maximum rate of rise of the Na spikes at a high resting potential level at which Na inactivation was completely depressed. Compared to Na spikes, Ca spikes were less sensitive to TTX and procaine. Ganglion cells were also capable of producing action potentials (Sr spikes) in an isotonic SrCl(2) solution and prolonged action potentials in an isotonic BaCl(2) solution, but these cells were rendered inexcitable in an isotonic MgCl(2) solution. The peak level of the Sr spikes was dependent on the external Sr concentration and was insensitive to both TTX and procaine. Sr ions, like Ca ions, reduced Na inactivation during the resting state, and depressed the maximum rate of rise of the Na spikes at a high resting potential level. It was concluded that Ca (and Sr) ions exert dual actions on the membrane; namely, regulating the Na permeability and acting as charge carriers during the active state of the membrane.
牛蛙交感神经节细胞能够在等渗（84 mM）氯化钙溶液中产生动作电位（钙峰）。钙峰的峰值水平随着钙浓度增加10倍而显示出约30 mV的升高。在含有相对高钙和相对低钠的溶液中产生动作电位期间，钠以及钙离子都能够作为电荷载体。外部钙浓度的降低在固定静息电位水平时降低了最大上升速率，并在完全抑制钠失活的高静息电位水平时增加了钠峰的最大上升速率。与钠峰相比，钙峰对河豚毒素（TTX）和普鲁卡因的敏感性较低。神经节细胞也能够在等渗氯化锶溶液中产生动作电位（锶峰），并在等渗氯化钡溶液中产生延长的动作电位，但这些细胞在等渗氯化镁溶液中变得不可兴奋。锶峰的峰值水平取决于外部锶浓度，并且对TTX和普鲁卡因均不敏感。与钙离子一样，锶离子在静息状态下减少钠失活，并在高静息电位水平时降低钠峰的最大上升速率。得出的结论是，钙（和锶）离子对膜发挥双重作用；即，在膜的活动状态期间调节钠通透性并作为电荷载体。
