Propagated action potentials can be obtained in canine cardiac Purkinje fibers exposed to Na-free solutions containing no inorganic cation other than Ca and K. Essentially similar action potentials are obtained if Na is replaced by tetraethylammonium (TEA), tetramethylammonium (TMA), or choline. In a solution containing 128 mM TEA and 16.2 mM Ca the characteristics of these electrical responses were: maximum diastolic potential, -59 ± 3.3 mV; overshoot, 20 ± 6.8 mV; maximum upstroke velocity, 3.7 ± 2.3 V/s; conduction velocity, 0.1 m/s; and action potential duration, 360 ± 45 ms. The magnitude of the overshoot varied with log Ca o with a slope of about 30 mV/10-fold concentration change. The upstroke velocity was an approximately linear function of Ca o . The active response was greatly diminished or abolished by Mn and D-600 but was unaffected by tetrodotoxin. These Ca-dependent responses appeared in a region of transmembrane potential (about -50 mV) at which the rapid Na-dependent upstroke is abolished even when Na is present.
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机译：在暴露于含有无机阳离子的甘氨酸心脏紫癜纤维中可以在含有无机阳离子的无机阳离子外，获得的传播动作电位在基本上获得类似的动作电位，如果Na被四乙基铵（茶），四甲基铵（TMA）或胆碱代替。在含有128毫米茶和16.2毫米CA的溶液中，这些电反应的特性是：最大舒张电位，-59±3.3mV;过冲，20±6.8 mV;最大上行程速度，3.7±2.3 v / s;传导速度，0.1米/秒;和动作潜在持续时间，360±45毫秒。过冲的幅度随着LOG CA O而变化，具有约30mV / 10倍浓度变化的斜率。上行速度是CA O的大致线性函数。通过Mn和D-600大大减少或消除了活性反应，但不受四抗毒素的影响。这些Ca依赖性反应出现在跨膜电位（约-50mV）的区域中，即使在存在Na时也被废除了快速Na依赖性上午。
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