Control of maximum sarcoplasmic reticulum Ca load in intact ferret ventricular myocytes -: Effects of thapsigargin and isoproterenol
Control of maximum sarcoplasmic reticulum Ca load in intact ferret ventricular myocytes -: Effects of thapsigargin and isoproterenol
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DOI：
10.1085/jgp.111.4.491
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发表时间：
1998-04-01
影响因子：
3.8
通讯作者：
Bers, DM
中科院分区：
文献类型：
--
作者：
Ginsburg, KS;Wieber, CR;Bers, DM
在稳定状态下，心肌细胞肌浆网（SR）的钙含量由内流和外流途径之间的平衡决定。SR Ca含量可能主要受SR和胞质溶胶之间的梯度中固有的ATP提供的化学势限制。也就是说，从胞质溶胶到SR的正向Ca泵送可能会受到依赖于SR内自由[Ca]的能量保守反向泵送的反对。另一方面，SR Ca负载可能受到耗散途径（泵滑移和/或泵独立泄漏）的限制。为了评估SR Ca含量是如何受到限制的，我们通过L型Ca通道（I-Ca）用已知量的Ca累积加载电压钳位雪貂心室肌细胞，使用无Na溶液来防止Na/Ca交换。然后，我们测量了在控制条件下产生的最大咖啡因释放的SR Ca含量，以及当SR Ca泵被异丙肾上腺素（1 μ M）加速或被毒胡萝卜素（0.2-0.4 μ M）减慢时。在控制条件下，SR Ca含量达到137 μ mol的极限。当通过积分咖啡因诱导的Na/Ca交换电流（积分I（NaCaX）dt）和119 μ mol .当使用依赖于胞质游离Ca（[Ca]（i））变化的荧光信号测量时，当Thapsigargin使Ca-ATP酶泵速减慢39%时，最大肌浆网Ca含量降低5（积分I（NaCaX）dt法）或23%（荧光法），当异丙肾上腺素使泵速增加74%时，肌浆网Ca含量增加10%（荧光法）或20%（积分I（NaCaX）dt法）。SR Ca负载的相对稳定性表明，耗散损失在设置SR Ca含量时仅具有微小的影响。事实上，似乎完整细胞中的SR Ca泵可以产生接近热力学极限的[Ca]梯度。
In steady state, the Ca content of the sarcoplasmic reticulum (SR) of cardiac myocytes is determined by a balance among influx and efflux pathways. The SR Ca content may be limited mainly by the ATP-supplied chemical potential that is inherent in the gradient between SR and cytosol. That is, forward Ca pumping from cytosol to SR may be opposed by energetically conservative reverse pumping dependent on intra-SR free [Ca]. On the other hand, SR Ca loading may be limited by dissipative pathways (pump slippage and/or pump-independent leak). To assess how SR Ca content is limited, we loaded voltage-clamped ferret ventricular myocytes cumulatively with known amounts of Ca via L-type Ca channels (I-Ca), using Na-free solutions to prevent Na/Ca exchange. We then measured the maximal resulting caffeine-released SR Ca content under control conditions, as well as when SR Ca pumping was accelerated by isoproterenol (1 mu M) or slowed by thapsigargin (0.2-0.4 mu M) Under control conditions, SR Ca content reached a limit of 137 mu mol . liter cytosol(-1) (nonmitochondrial volume) when measured by integrating caffeine-induced Na/Ca exchange currents (integral I(NaCaX)dt) and of 119 mu mol . liter cytosol(-1) when measured using fluorescence signals dependent on changes in cytosolic free Ca ([Ca](i)). When Ca-ATPase pumping rate was slowed 39% by thapsigargin, the maximal SR Ca content decreased by 5 (integral I(NaCaX)dt method) or 23% (fluorescence method); when pumping rate was increased 74% by isoproterenol, SR Ca content increased by 10% (fluorescence method) or 20% (integral I(NaCaX)dt method). The relative stability of the SR Ca load suggests that dissipative losses have only a minor influence in setting the SR Ca content. Indeed, it appears that the SR Ca pump in intact cells can generate a [Ca] gradient approaching the thermodynamic limit.