Dascal N, Gillo B, Lass Y
J Physiol. 1985 Sep;366:299-313. doi: 10.1113/jphysiol.1985.sp015799.
The involvement of Ca ions in the mediation of muscarinic Cl- current responses in Xenopus oocytes was studied using the voltage-clamp technique and direct measurements of 45Ca efflux. The injection of Ca into the oocytes produced a dose-dependent transient inward (depolarizing) current carried by Cl. This current was occasionally followed by a second, long-lasting inward current. The muscarinic response was evoked by the application of acetylcholine (ACh). It consisted of a transient inward current response, and a long-lasting inward current response, both inward currents carried by Cl ions. Both responses were inhibited by intracellular injection of ethyleneglycol-bis-(beta-aminoethylether)N,N'-tetraacetic acid (EGTA), the long-lasting response being inhibited faster than the transient response. The calmodulin inhibitor, trifluoperazine, inhibited both the Cl-current responses to ACh and to Ca injection. ACh (10 microM) evoked a release of 45Ca from pre-loaded oocytes. This effect was inhibited by atropine (1 microM). In the absence of external Ca, the muscarinic transient and long-lasting responses were partially inhibited. The long-lasting response was more sensitive to the external Ca depletion than the transient response. Repetitive applications of ACh in the absence of external Ca resulted in a progressive decrease in the response amplitudes. Under these conditions, a temporary exposure to normal Ca solution ('Ca window') resulted in a partial recovery of the response amplitudes. The muscarinic inward current responses were not inhibited by nifedipine (20 microM). In the presence of a high external concentration of Mn ions ([Mn]o = 18 mM), the transient response was potentiated. Subsequent applications of ACh in high [Mn]o resulted in progressively decreasing responses. It is concluded that the muscarinic Cl responses in Xenopus oocytes are mediated by an increase in the intracellular free Ca activity, aiCa. Ca ions involved in the mediation of the muscarinic Cl current responses are released from cellular Ca stores. It is also proposed that the transient and long-lasting responses result from the release of Ca from two different stores.
利用电压钳技术和对45Ca外流的直接测量，研究了钙离子在非洲爪蟾卵母细胞毒蕈碱型氯离子电流反应介导中的作用。向卵母细胞内注射钙离子会产生由氯离子携带的剂量依赖性瞬时内向（去极化）电流。该电流偶尔会继之以第二个持久的内向电流。毒蕈碱反应由乙酰胆碱（ACh）的应用所诱发。它包括一个瞬时内向电流反应和一个持久的内向电流反应，这两种内向电流均由氯离子携带。两种反应都被细胞内注射乙二醇双（β-氨基乙基醚）N,N'-四乙酸（EGTA）所抑制，持久反应的抑制速度比瞬时反应更快。钙调蛋白抑制剂三氟拉嗪抑制了对ACh和对钙离子注射的氯离子电流反应。ACh（10微摩尔）引起了预加载卵母细胞中45Ca的释放。这种效应被阿托品（1微摩尔）所抑制。在没有外部钙离子的情况下，毒蕈碱型瞬时和持久反应被部分抑制。持久反应比瞬时反应对外界钙离子耗竭更敏感。在没有外部钙离子的情况下重复应用ACh导致反应幅度逐渐降低。在这些条件下，暂时暴露于正常钙离子溶液（“钙离子窗口”）导致反应幅度部分恢复。毒蕈碱型内向电流反应不被硝苯地平（20微摩尔）所抑制。在外部高浓度锰离子（[Mn]o = 18毫摩尔）存在的情况下，瞬时反应增强。随后在高[Mn]o条件下应用ACh导致反应逐渐降低。结论是非洲爪蟾卵母细胞中的毒蕈碱型氯离子反应由细胞内游离钙离子活性aiCa的增加所介导。参与毒蕈碱型氯离子电流反应介导的钙离子从细胞钙库中释放。还提出瞬时和持久反应是由从两个不同钙库中释放钙离子所致。
