Kettlun Claudia, González Adom, Ríos Eduardo, Fill Michael
Department of Physiology, Loyola University Chicago, 2160 S. First Ave., Maywood, IL 60153, USA.
J Gen Physiol. 2003 Oct;122(4):407-17. doi: 10.1085/jgp.200308843. Epub 2003 Sep 15.
Ryanodine receptor (RyR) channels from mammalian cardiac and amphibian skeletal muscle were incorporated into planar lipid bilayers. Unitary Ca2+ currents in the SR lumen-to-cytosol direction were recorded at 0 mV in the presence of caffeine (to minimize gating fluctuations). Currents measured with 20 mM lumenal Ca2+ as exclusive charge carrier were 4.00 and 4.07 pA, respectively, and not significantly different. Currents recorded at 1-30 mM lumenal Ca2+ concentrations were attenuated by physiological [K+] (150 mM) and [Mg2+] (1 mM), in the same proportion (approximately 55%) in mammalian and amphibian channels. Two amplitudes, differing by approximately 35%, were found in amphibian channel studies, probably corresponding to alpha and beta RyR isoforms. In physiological [Mg2+], [K+], and lumenal [Ca2+] (1 mM), the Ca2+ current was just less than 0.5 pA. Comparison of this value with the Ca2+ flux underlying Ca2+ sparks suggests that sparks in mammalian cardiac and amphibian skeletal muscles are generated by opening of multiple RyR channels. Further, symmetric high concentrations of Mg2+ substantially reduced the current carried by 10 mM Ca2+ (approximately 40% at 10 mM Mg2+), suggesting that high Mg2+ may make sparks smaller by both inhibiting RyR gating and reducing unitary current.
来自哺乳动物心脏和两栖动物骨骼肌的雷诺丁受体（RyR）通道被整合到平面脂质双分子层中。在咖啡因存在的情况下（以尽量减少门控波动），在0 mV下记录了从肌浆网腔到细胞质方向的单位Ca2+电流。以20 mM腔Ca2+作为唯一电荷载体测量的电流分别为4.00和4.07 pA，且无显著差异。在1 - 30 mM腔Ca2+浓度下记录的电流在生理[K+]（150 mM）和[Mg2+]（1 mM）存在时会衰减，在哺乳动物和两栖动物通道中衰减比例相同（约55%）。在两栖动物通道研究中发现了两种幅度相差约35%的电流，可能分别对应α和β RyR亚型。在生理[Mg2+]、[K+]和腔[Ca2+]（1 mM）条件下，Ca2+电流略小于0.5 pA。将该值与Ca2+火花背后的Ca2+通量进行比较表明，哺乳动物心脏和两栖动物骨骼肌中的火花是由多个RyR通道开放产生的。此外，对称的高浓度Mg2+显著降低了由10 mM Ca2+携带的电流（在10 mM Mg2+时约降低40%），这表明高Mg2+可能通过抑制RyR门控和降低单位电流使火花变小。
