期刊
JOURNAL OF MEMBRANE BIOLOGY
卷 187, 期 1, 页码 51-64出版社
SPRINGER
DOI: 10.1007/s00232-001-0150-x
关键词
calcium release channel; ryanodine receptors; sarcoplasmic reticulum; excitation-contraction coupling; intracellular calcium
资金
- NHLBI NIH HHS [HL 057832, HL 32711] Funding Source: Medline
The block of rabbit skeletal ryanodine receptors (RyR1) and dog heart RyR2 by cytosolic [Mg2+], and its reversal by agonists Ca2+, ATP and caffeine was studied in planar bilayers. Mg2+ effects were tested at submaximal activating [Ca2+] (5 muM). Approximately one third of the RyR1s had low open probability (LA channels) in the absence of Mg2+. All other RyR1s displayed higher activity (HA channels). Cytosolic Mg2+ (I mM) blocked individual RyR1 channels to varying degrees (32 to 100%). LA channels had residual P-o < 0.005 in I mM Mg2+ and reactivated poorly with [Ca2+] (100 muM), caffeine (5 mm), or ATP (4 mm; all at constant I mM Mg2+). HA channels had variable activity in Mg2+ and variable degree of recovery from Mg2+ block with Ca2+, caffeine or ATP application. Nearly all cardiac RyR2s displayed high activity in 5 gm [Ca2+]. They also had variable sensitivity to Mg2+. However, the RyR2s consistently recovered from Mg2+ block with 100 muM [Ca2+] or caffeine application, but not when ATP was added. Thus, at physiological [Mg2+], RyR2s behaved as relatively homogeneous Ca2+/caffeine-gated HA channels. In contrast, RyR1s displayed functional heterogeneity that arises from differential modulatory actions of Ca2+ and ATP. These differences between RyR1 and RyR2 function may reflect their respective roles in muscle physiology and excitation-contraction coupling.
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