Miller D J, Mörchen A
J Gen Physiol. 1978 Jan;71(1):47-67. doi: 10.1085/jgp.71.1.47.
Resting and action potentials were recorded from superfused strips of frog ventricle. Reducing the bathing calcium concentration ([Ca2+]0) with or without ethylene glycol-bis(beta-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA) prolongs the action potential (AP). The change in the duration of the AP extends over many minutes, but is rapidly reversed by restoring calcium ions. Other changes (e.g., in resting potential and overshoot) are, however, only more slowly reversed. Reducing [Ca2+]0 with 0.2, 2, or 5 mM EGTA produces progressively greater prolongation of AP; maximum values were well in excess of 1 min. This prolongation can be reversed by other divalent cations in EGTA (Mg2+, Sr2+) or Ca-free (Mn2+) solutions, or by acetylcholine. Barium ions increase AP duration in keeping with their known effect on potassium conductance. D600, which blocks the slow inward current in cardiac muscle, is without effect on the action potentials recorded in EGTA solutions, or on the time course and extent of the recovery to normal duration upon restoring calcium ions. It is concluded that divalent cations exert an influence on membrane potassium conductance extracellularly in frog heart. The cell membrane does not become excessively "leaky" in EGTA solutions.
从蛙心室的灌流条带记录静息电位和动作电位。在有或没有乙二醇双（β-氨基乙基醚）N，N，N'，N'-四乙酸（EGTA）的情况下降低浴液钙浓度（[Ca2+]0）会延长动作电位（AP）。动作电位持续时间的变化会持续许多分钟，但通过恢复钙离子可迅速逆转。然而，其他变化（例如静息电位和超射的变化）仅更缓慢地逆转。用0.2、2或5 mM EGTA降低[Ca2+]0会使动作电位的延长逐渐增加；最大值远超过1分钟。这种延长可被EGTA中的其他二价阳离子（Mg2+、Sr2+）或无钙（Mn2+）溶液中的二价阳离子或乙酰胆碱逆转。钡离子会增加动作电位持续时间，这与其对钾电导的已知作用一致。D600可阻断心肌中的缓慢内向电流，但对在EGTA溶液中记录的动作电位或恢复钙离子后恢复到正常持续时间的时间进程和程度没有影响。得出的结论是，二价阳离子在蛙心细胞外对膜钾电导有影响。在EGTA溶液中细胞膜不会变得过度“渗漏”。
