The spark and its ember -: Separately gated local components of Ca2+ release in skeletal muscle

被引:65
作者
González, A
Kirsch, WG
Shirokova, N
Pizarro, G
Stern, MD
Ríos, E
机构
[1] Rush Univ, Dept Mol Biophys & Physiol, Chicago, IL 60612 USA
[2] Univ Republ, Fac Med, Dept Biofis, Montevideo, Uruguay
[3] NIA, Cardiovasc Sci Lab, NIH, Baltimore, MD 21224 USA
关键词
excitation-contraction coupling; calcium sparks; ryanodine receptors; caffeine magnesium;
D O I
10.1085/jgp.115.2.139
中图分类号
Q4 [生理学];
学科分类号
071003 ;
摘要
Amplitude, spatial width, and rise time of Ca2+ sparks were compared in hog fast-twitch muscle, in three conditions that alter activation of release channels by [Ca2+]. A total of similar to 17,000 sparks from 30 cells were evaluated. In cells under voltage clamp, caffeine (0.5 or 1 mM) increased average spark width by 28%, rise time by 18%, and amplitude by 7%. Increases in width were significant even among events of the same rise time. Spontaneous events recorded in permeabilized fibers with low internal [Mg2+] (0.4 mM), had width and rise times greater than in reference, and not significantly different than those in caffeine. The spark average in reference rides on a continuous fluorescence "ridge" and is continued by an "ember," a prolongation of width similar to 1 mu m and amplitude <0.2, vanishing in similar to 100 ms. Ridge and ember were absent in caffeine and in permeabilized cells. Ex posure of voltage-clamped cells to high internal [Mg2+] (7 mM) had effects opposite to caffeine, reducing spark width by 26% and amplitude by 27%. In high [Mg2+], the ember was visible in individual sparks as a prolongation of variable duration and amplitude up to 1.2. Based on simulations and calculation of Ca2+ release flux from averaged sparks, the increase in spark width caused by caffeine was interpreted as evidence of an increase in radius of the release source-presumably by recruitment of additional channels. Conversely, spark narrowing suggests loss of contributing channels in high Mg2+. Therefore, these changes in spark width at constant rise times are evidence of a multichannel origin of sparks. Because ridge and ember were reduced by promoters of Ca2+-dependent activation (caffeine, low [Mg2+]) and became more visible in the presence of its inhibitors, they are probably manifestations of Ca2+ release directly operated by voltage sensors.
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页码:139 / 157
页数:19
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