Ohba M, Kishi M, Kawata H
Jpn J Physiol. 1984;34(5):803-13. doi: 10.2170/jjphysiol.34.803.
The effects of hypotonic solution on the mechanical activities and action potential of the bullfrog atrium were investigated. Exposure of muscle to hypotonic solutions (70% of normal solution) produced initially a transient increase in twitch after which twitch declined below the control level. The response is independent of the kinds of salts withdrawn to make the medium hypotonic and of the presence of beta-blocker (5 X 10(-7) M propranolol). The resting potential and the plateau level of action potential were little changed initially. When the twitch declined, a small amount of depolarization and a shortening of action potential duration were observed; however, the plateau level of action potential was not reduced. The initial increase in twitch was not observed, and only the gradual decline of twitch remained in the caffeine containing hypotonic solution. The weight of muscle increased 10% in the hypotonic solution. The resting tension was also increased transiently and then declined to reach a maintained plateau with exposure to hypotonic solution. In the 0-Ca2+ or caffeine containing medium, the transient component of contracture was suppressed but the plateau tension remained. It is suggested that the initial transient increase of twitch by the perfusion of the hypotonic solution was induced by the Ca2+ released from the sarcoplasmic reticulum (SR), and the resultant decline of twitch resulted from the depletion of Ca2+ from the SR and/or from the shortening of action potential duration.
研究了低渗溶液对牛蛙心房机械活动和动作电位的影响。将肌肉暴露于低渗溶液（正常溶液的70%）中，最初会使抽搐短暂增加，之后抽搐下降至对照水平以下。该反应与为使培养基低渗而去除的盐的种类以及β受体阻滞剂（5×10⁻⁷M普萘洛尔）的存在无关。静息电位和动作电位的平台期最初变化不大。当抽搐下降时，观察到少量去极化和动作电位持续时间缩短；然而，动作电位的平台期并未降低。在含咖啡因的低渗溶液中未观察到抽搐的初始增加，仅保留了抽搐的逐渐下降。在低渗溶液中肌肉重量增加了10%。静息张力也短暂增加，然后随着暴露于低渗溶液而下降至维持的平台期。在无钙或含咖啡因的培养基中，挛缩的短暂成分受到抑制，但平台张力仍然存在。提示低渗溶液灌注引起的抽搐最初短暂增加是由肌浆网（SR）释放的Ca²⁺诱导的，随后抽搐下降是由于SR中Ca²⁺的耗竭和/或动作电位持续时间的缩短所致。
