Santi C M, Conner J A, Hernández-Cruz A
Departamento de Neurociencias, Instituto de Fisiología Celular, UNAM, México City, México.
Cell Signal. 1995 Nov;7(8):803-20. doi: 10.1016/0898-6568(95)02008-x.
Ca2+ mobilization elicited by simulation with brief pulses of high K+ were monitored with confocal laser scanned microscopy in intact, guinea pig cardiac myocytes loaded with the calcium indicator fluo-3. Single wavelength ratioing of fluorescence images obtained after prolonged integration times revealed non-uniformities of intracellular Ca2+ changes across the cell, suggesting the presence of significant spatial Ca2+ gradients. Treatment with 20 microM ryanodine, an inhibitor of Ca2+ release from the SR, and 10 microM verapamil, a calcium channel blocker, reduced by 42% and 76% respectively the changes in [Ca2+]i elicited by membrane depolarization. The overall spatial distribution of [Ca2+]i changes appeared unchanged. Ca2+ transients recorded in the presence of verapamil and ryanodine (about 20% of the size of control responses), diminished in the presence of 50 microM 2-4 Dichlorbenzamil (DCB) or 5 mM nickel, two relatively specific inhibitors of the Na+/Ca2+ exchange mechanism. Conversely, when the reversal potential of the Na+/Ca2+ exchange was shifted to negative potentials by lowering [NA+]o or by increasing [Na+]i by treatment with 20 microM monensin, the amplitude of these Ca2+ transients increased. Ca2+ transients elicited by membrane depolarization and largely mediated by reverse operation of Na(+)-Ca2+ exchange could be recorded in the presence of ryanodine, verapamil and monensin. These finding suggest that in intact guinea pig cardiac cells, Ca2+ influx through the Na+/Ca2+ exchange mechanism activated by a membrane depolarization in the physiological range can be sufficient to play a significant role in excitation-contraction coupling.
在装载有钙指示剂fluo-3的完整豚鼠心肌细胞中，利用共聚焦激光扫描显微镜监测高钾短暂脉冲刺激引发的Ca2+动员。长时间积分后获得的荧光图像的单波长比率显示，整个细胞内Ca2+变化不均匀，提示存在显著的空间Ca2+梯度。用20微摩尔的ryanodine（一种肌浆网Ca2+释放抑制剂）和10微摩尔的维拉帕米（一种钙通道阻滞剂）处理，分别使膜去极化引发的[Ca2+]i变化降低了42%和76%。[Ca2+]i变化的整体空间分布似乎未改变。在维拉帕米和ryanodine存在下记录的Ca2+瞬变（约为对照反应大小的20%），在50微摩尔的2-4二氯苯甲酰胺（DCB）或5毫摩尔镍（两种相对特异性的Na+/Ca2+交换机制抑制剂）存在时减小。相反，当通过降低[Na+]o或将[Na+]i增加20微摩尔莫能菌素处理使Na+/Ca2+交换的反转电位移向负电位时，这些Ca2+瞬变的幅度增加。在ryanodine、维拉帕米和莫能菌素存在下可记录到由膜去极化引发且主要由Na(+)-Ca2+交换反向运作介导的Ca2+瞬变。这些发现提示，在完整的豚鼠心脏细胞中，在生理范围内由膜去极化激活的通过Na+/Ca2+交换机制的Ca2+内流足以在兴奋-收缩偶联中发挥重要作用。
