Ionic channel mechanisms underlying rhythmic membrane hyperpolanzation assoaated with muscle contraction in myocytes isolated from insect visceral muscle

从蟋蟀侧输卵管分离的肌细胞具有自发性节律性收缩。在电流湿条件下，用全细胞膜片钳技术进行的电记录清楚地表明，节律性收缩与瞬时膜超极化密切相关。这种节律性的膜超极化（RMH）的频率增加细胞外C？而随着细胞外Ca^2+浓度的降低或在电解液中加入非选择性阳离子通道（NSCC）阻断剂钆（gadolinium），细胞外Ca ^2+浓度降低。上述结果表明，RMH的产生与肌细胞膜上Ca^2+通道的Ca ^2+内流有关。通过膜片钳技术，我已经证明了在心肌细胞中存在两种类型的Ca^2+传导通道。一个是电压依赖性L型Ca^2+通道，另一个是牵张激活的Ca^2+传导非选择性阳离子通道。这些渠道很容易分布， ...更多信息 基于它们的电压依赖性、离子选择性、膜拉伸敏感性和药理学性质而被发现。本研究结果还表明，通过NSCC的Ca^<2+>内流可能通过将Ca^<2+>重新填充到蟋蟀输卵管肌细胞的内部Ca^<2+>库中而在RMH的产生中起重要作用。我尝试用膜片阻尼技术来鉴定钙依赖性钾通道.我已经证明了存在两种类型的Ca^2+激活的K通道。一种是高电导Ca^（2+）激活的K通道（BK通道），另一种是中间激活的K通道（1K通道）.在对称高K条件下，前者的单沟道电导为140 pS，后者的单沟道电导为50 pS。这些通道根据它们的电压依赖性、细胞内Ca^<2+>依赖性和药理学特性而被区分。目前的结果还表明，钙离子动员剂如咖啡因和兰尼碱的应用，抑制RMH的产生，也抑制肌肉收缩。这一结果表明，通过Ca^<2+>诱导的Ca ^<2 +>释放（CICR）机制从内部Ca^<2 +>库释放的Ca ^<2 +>参与了RMS的产生。目前的结果表明，在从蟋蟀侧输卵管分离的肌细胞中，与RMH相关的节律性收缩是由内部Ca^2+释放的Ca^2+诱导的。细胞内Ca^<2+>的增加可能激活BK或1K通道，从而诱导膜超极化。Ca^2+内流主要通过牵张激活的非选择性阳离子通道，可能通过CICR机制直接或间接地提供Ca^2+，在肌肉收缩中发挥重要作用。少

Myocytes isolated from the cricket lateral oviduct exhibit spontaneous rhythmic contraction Electrical recordings with the whole-cell patch damp technique under the current damp condition dearly showed that the rhythmic contraction is closely associated with the transient membrane hyperpolarization. The frequency of this rhythmic membrane hyperpolarization (RMH) increased with increasing extracellular C? whereas decreased with decreasing extracellular Ca^<2+> or with adding gadolinium, a blocker of nonselective cation channel (NSCC), into a bath solution. These results indicate that Ca^<2+> influx through Ca^<2+>-conducting channel in plasma membrane of myoccytes is responsible for the generation of RMH. By using the patch clamp technique, I have shown the presence of two types of Ca^<2+> -conducting channels in myocytes. One is a voltage-dependent L-type Ca^<2+> channel and the other is a stretch-activated Ca^<2+>-conducting nonselective cation channel. These channels are readily dist … More inguished on the basis of their voltage dependency ion selectivity membrane stretch sensitivity and pharmacological properties. The present results also indicated that Ca^<2+> influx through NSCC, may play an important role in the generation of RMH Via refilling Ca^<2+> into internal Ca^<2+> store in myocytes isolated from the cricket lateral oviduct.In order to identify the ionic channels responsible for the generation of membrane hyperpolarization, I tried to identify the Ca^<2+>-dependent K channels by using the patch damp technique. I have shown the presence of two types of Ca^<2+>-activated K channels. One is a high conductance Ca^<2+>-activated K channel (BK channel and the other is a intermediate -activated K channel (1K channel). The former channel had the single channel conductance of 140 pS and the latter channel of 50 pS wtith symmetrical high K condition. These channels are distinguished on the basis of their voltage dependency intracellular Ca^<2+> dependency and pharmacological properties. The present results have also revealed that the application of Ca^<2+> mobilizers such as caffeine and ryanodine, inhibited the generation of RMH and also the muscle contraction. This result indicates that the released Ca^<2+> from the ineternal Ca^<2+> store via Ca^<2+>-induced Ca^<2+> release (CICR) mechanism is involved in the generation of RMS.In conclusion, the present results indicate that rhythmic contraction associated with RMH in myocytes isolated from the cricket lateral oviduct is induced by released Ca^<2+> from the internal Ca^<2+> store site and a resultant increase in the intracellular Ca^<2+> may activate BK or 1K channels and thereby induce membrane hyperpolarization. Ca^<2+> influx mainly through stretch activated nonselective cation channel may play an important role for muscle contraction via supplying Ca^<2+> directly or indirectly through CICR mechanism. Less