Arlock P, Katzung B G
J Physiol. 1985 Mar;360:105-20. doi: 10.1113/jphysiol.1985.sp015606.
We used ouabain-treated guinea-pig and ferret papillary muscles to study transient inward current (Iti), after-contractions, and tonic tension development during voltage-clamp pulses. Li, sucrose and choline were used isosmotically as Na substitutes to evaluate the effect of altering the Na equilibrium potential. We were unable to detect outward Iti at any potential up to +30 mV in normal or Na-depleted solutions. However, reduction of Na had a biphasic effect on Iti, initially increasing it and then reducing it at all clamp potentials from -50 to +20 mV. After-contractions were also initially increased and, in sufficiently Na-depleted solutions, decreased by reduction of extracellular Na. However, the peak in the after-contraction always occurred later than the increase in Iti and frequently coincided with the maximum suppression of the current. Complete suppression of after-contractions was not often achieved and always required more complete Na replacement than Iti suppression. Tonic tension responses were reduced by Na replacement, usually in synchrony with the reduction of Iti. The responses of Iti to Na replacement are consistent with a model of electrogenic Na-Ca exchange over the potential range positive to -50 mV. The responses deviate from the predictions of the model at more negative potentials. The results are consistent with the previous proposal that oscillatory changes in internal free Ca concentration underlie both Iti and after-contractions.
我们使用哇巴因处理过的豚鼠和雪貂乳头肌来研究电压钳脉冲期间的瞬时内向电流（Iti）、后收缩以及强直张力的发展。用等渗的锂、蔗糖和胆碱作为钠替代物，以评估改变钠平衡电位的影响。在正常溶液或钠缺失溶液中，我们在高达+30 mV的任何电位下都未能检测到外向Iti。然而，钠的减少对Iti有双相作用，最初使其增加，然后在从 -50到+20 mV的所有钳制电位下又使其降低。后收缩最初也增加，并且在足够钠缺失的溶液中，细胞外钠的减少使其降低。然而，后收缩的峰值总是比Iti的增加出现得晚，并且经常与电流的最大抑制同时发生。后收缩的完全抑制并不常见，并且总是比Iti抑制需要更完全的钠替代。强直张力反应通过钠替代而降低，通常与Iti的降低同步。在正于 -50 mV的电位范围内，Iti对钠替代的反应与电生钠 - 钙交换模型一致。在更负的电位下，反应偏离该模型的预测。这些结果与先前的提议一致，即细胞内游离钙浓度的振荡变化是Iti和后收缩的基础。
