摘要
以前结果表明 ,ryanodine受体 (ryanodinereceptors ,RyRs)门控的咖啡因敏感的钙库和钙引钙释放(Ca2 + inducedCa2 +release ,CICR)机制存在于鲫鱼视网膜ON型双极细胞的胞体中[1] 。采用RyRs的免疫细胞化学方法和细胞内钙测量技术 ,我们进一步研究了RyRs门控的钙库是否存在于这些细胞的轴突末梢中。视网膜纵切和分离细胞的免疫细胞化学研究显示 ,RyRs主要位于ON型双极细胞的胞体中。咖啡因浓度升至 4 0mmol/L在轴突末梢不能诱导钙信号。在细胞外K+浓度升至 10mmol/L引起静息 [Ca2 +]i 轻微升高后 ,咖啡因在轴突末梢也不能诱导钙信号。在forskolin或多巴胺引起细胞内cAMP浓度升高 ,进而cAMP依赖的磷酸化增强后 ,咖啡因在轴突末梢仍不能诱导钙信号。此外 ,50 μmol/Lryanodine对 65mmol/LK+作用 1min或 2min诱导的轴突末梢的钙信号没有产生任何效应。这些结果表明 。
It has been shown previously that caffeine sensitive Ca 2+ stores gated by ryanodine receptors (RyRs) and the mechanism of Ca 2+ induced Ca 2+ release (CICR) exist in the soma of carp retinal ON type bipolar cells [1] . Using immunocytochemistry of RyRs and intracellular Ca 2+ measurement, we further investigated whether RyR gated Ca 2+ stores are present in the terminal of these cells. Immunocytochemical study of both vertical section and dissociated cells of the retina indicates that RyRs were mainly localized in the soma of ON type bipolar cells. Caffeine up to 40 mmol/L could not induce Ca 2+ signal in the terminal. After resting [Ca 2+ ] i was slightly increased by raising external K + to 10 mmol/L, no Ca 2+ signal was induced by caffeine in the terminal. In the presence of forskolin or dopamine, by which intracellular cAMP and in turn cAMP dependent phosphorylation are enhanced, caffeine also failed to bring Ca 2+ signal in the terminal. In addition, 50 μmol/L ryanodine did not show any effect on Ca 2+ signal evoked by 65 mmol/L K + for 1 min or 2 min in the terminal. Taken together, it is indicated that RyR gated caffeine sensitive Ca 2+ stores and CICR are absent in the terminal of carp retinal ON type bipolar cells.
