Extracellular calcium participates in responses to acetylcholine in Xenopus oocytes

FEBS Letters

Lupu-Meiri, Monica¹  Shapira, Hagit¹  Oron, Yoram¹ 

[1] Division of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel

关键词: Calcium channel;    Inositol phosphate;    Chloride current;    Muscarinic response;    Xenopus oocyte;   

DOI  :  10.1016/0014-5793(90)80180-Q

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

We tested the contribution of extracellular calcium (Ca_o ²⁺) to membrane electrical responses to acetylcholine (ACh) in native Xenopus oocytes. Removal of Ca_o caused a decrease in both the rapid (D₁) and the slow (D₂) chloride currents that comprise the common depolarizing response to ACh in native oocyte. The effect of Ca_o ²⁺ removal on the muscarinic response was mimicked by the addition of 1 mM Mn²⁺, an effective antagonist of calcium influx, though not by antagonists of voltage-sensitive calcium channels. When oocytes were challenged with ACh in Ca²⁺-free medium, subsequent addition of 1.8 mM CaCl₂ resulted in a rapid, often transient, depolarizing current. Similarly to the Ca_o ²⁺-dependent component of membrane electrical responses, the Ca²⁺ -evoked current was reversibly abolished by Mn²⁺, though not by antigonists of voltage-sensitive calcium channels. Depletion of cellular calcium potentiated the Ca²⁺-evoked current, implying negative feedback of calcium channels by calcium. Injection of 10–100 fmol ofinositol 1,4,5-trisphosphate (IP₃) resulted in a two-component depolarizing current. IP₃ injection promoted the appearance of Ca_o ²⁺-evoked current that was significantly potentiated by previous calcium depletion. We suggest that activation of cell-membrane muscarinic receptors causes opening of apparently voltage-insensitive and verapamil or diltiazem-resistant calcium channels. These channels may be activated by IP₃ or its metabolites, which increase following the activation of cell membrane receptors coupled to a phospholipase C. The channels may be identical to receptor-operated channels described in other model systems.

【 授权许可】

Unknown