Szentesi P, Kovács L, Csernoch L
Department of Physiology and Cell Physiology Research Group of the Hungarian Academy of Sciences, Medical and Health Sciences Centre, Medical School, University of Debrecen, Hungary.
J Physiol. 2000 Nov 1;528(Pt 3):447-56. doi: 10.1111/j.1469-7793.2000.00447.x.
Enzymatically dissociated fibres from the extensor digitorum communis muscle of rats were mounted into a double Vaseline gap chamber. The rate of calcium release (R(rel)) from the sarcoplasmic reticulum (SR) and changes in SR permeability to Ca2+ (PSR) were calculated from measured changes in intracellular calcium concentration. Calcium release during a prepulse attenuated the inactivating component of PSR of the subsequent test pulse. The suppression was graded, larger release causing greater suppression, as expected from a calcium-dependent inactivation process. However, if the dissociation constant of the putative inhibitory calcium binding site (Kd) was estimated using different test pulses different affinities were obtained: a smaller test pulse yielded a smaller Kd. Comparing the suppression of the inactivatable component of PSR during the test pulse (suppression) with the inactivatable component during the prepulse (pre-inactivation) revealed a linear relationship with a regression coefficient close to unity. Lowering intracellular magnesium by decreasing its concentration to 25 microM in the internal solution altered the time course of PSR. The maximal peak-to-steady-level ratio was increased to 6.3 +/- 0.4 (n = 10, mean +/- s.e.m.) from a control value of 3.0 +/- 0.2 (n = 19). Despite the apparent change in steady-state inactivation, suppression remained equal to that pre-inactivation. Our results support the view that a depolarizing pulse always recruits the same set of calcium release channels and a portion of these channels undergoes a deterministic inactivation process.
将大鼠趾长伸肌经酶解离后的纤维安装到双凡士林间隙室中。根据测量的细胞内钙浓度变化计算肌浆网（SR）的钙释放速率（R(rel)）和SR对Ca2+的通透性变化（PSR）。预脉冲期间的钙释放减弱了后续测试脉冲的PSR失活成分。这种抑制是分级的，释放量越大抑制作用越强，这与钙依赖性失活过程预期的一致。然而，如果使用不同的测试脉冲来估计假定的抑制性钙结合位点的解离常数（Kd），会得到不同的亲和力：较小的测试脉冲产生较小的Kd。比较测试脉冲期间PSR可失活成分的抑制（抑制）与预脉冲期间可失活成分（预失活），发现两者呈线性关系，回归系数接近1。通过将内部溶液中镁的浓度降低到25 microM来降低细胞内镁浓度，改变了PSR的时间进程。最大峰-稳态比从对照值3.0±0.2（n = 19）增加到6.3±0.4（n = 10，平均值±标准误）。尽管稳态失活有明显变化，但抑制作用仍与预失活时相等。我们的结果支持这样一种观点，即去极化脉冲总是募集相同的一组钙释放通道，并且这些通道中的一部分会经历一个确定性的失活过程。
