Kinetic studies of calcium-induced calcium release in cardiac sarcoplasmic reticulum vesicles

被引:19
作者
Sánchez, G
Hidalgo, C
Donoso, P
机构
[1] Univ Chile, Fac Med, ICBM, Santiago 7, Chile
[2] Ctr Estudios Cientif, Valdivia, Chile
关键词
D O I
10.1016/S0006-3495(03)75037-1
中图分类号
Q6 [生物物理学];
学科分类号
071011 ;
摘要
Fast Ca2+ release kinetics were measured in cardiac sarcoplasmic reticulum vesicles actively loaded with Ca2+. Release was induced in solutions containing 1.2 mM free ATP and variable free [Ca2+] and [Mg2+]. Release rate constants (k) were 10-fold higher at pCa 6 than at pCa 5 whereas Ryanodine binding was highest at pCa less than or equal to5. These results suggest that channels respond differently when exposed to sudden [Ca2+] changes than when exposed to Ca2+ for longer periods. Vesicles with severalfold different luminal calcium contents exhibited double exponential release kinetics at pCa 6, suggesting that channels undergo time-dependent activity changes. Addition of Mg2+ produced a marked inhibition of release kinetics at pCa 6 (K-0.5 = 63 muM) but not at pCa 5. Coexistence of calcium activation and inhibition sites with equally fast binding kinetics is proposed to explain this behavior. Thimerosal activated release kinetics at pCa 5 at all [Mg2+] tested and increased at pCa 6 the K-0.5 for Mg2+ inhibition, from 63 muM to 136 muM. We discuss the possible relevance of these results, which suggest release through RyR2 channels is subject to fast regulation by Ca2+ and Mg2+ followed by time-dependent regulation, to the physiological mechanisms of cardiac channel opening and closing.
引用
收藏
页码:2319 / 2330
页数:12
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