Fabiato A
J Gen Physiol. 1981 Nov;78(5):457-97. doi: 10.1085/jgp.78.5.457.
Intact cardiac cells from the adult rat or rabbit ventricle were isolated by enzymatic digestion with a progressive increase of the [free Ca2+] in the solution. These cells were electrically stimulated in the presence of 2.50 mM free Ca2+, and a twitch of maximum amplitude was elicited by the positive inotropic interventions that were found to be optimum. Then the cells were chemically skinned, and the maximum tension induced by a saturating [free Ca2+] was used as a reference to express the tension developed during the twitch of the intact cells. The myoplasmic [free Ca2+] reached during the twitch was inferred from the tension-pCa curve. In mechanically skinned cells of the same animal species, the myoplasmic [free Ca2+] reached during Ca2+-induced release of Ca2+ from the sarcoplasmic reticulum (SR) was inferred by two methods using (a) the tension-pCa curve and (b) a direct calibration of the transients of aequorin bioluminescence. The induction of a maximum Ca2+ release from the SR required a larger Ca2+ preload of the SR and a higher [free Ca2+] trigger in the rabbit than in the rat skinned cells. However, the results obtained with the two methods of inference of the myoplasmic [free Ca2+] suggest that in both animal species a maximum myoplasmic [free Ca2+] of pCa approximately 5.40 was reached during both the optimum Ca2+-induced release of Ca2+ from the SR of the skinned cells and the optimum twitch of the intact cells. This was much lower than the [free Ca2+] necessary for the full activation of the myofilaments (pCa approximately 4.90).
通过酶消化法分离成年大鼠或兔心室的完整心肌细胞,同时逐步增加溶液中的[游离Ca2+]浓度。在2.50 mM游离Ca2+存在的情况下对这些细胞进行电刺激,发现最佳的正性肌力干预可引发最大幅度的单次收缩。然后对细胞进行化学去膜处理,将饱和[游离Ca2+]诱导的最大张力用作参考,以表达完整细胞单次收缩过程中产生的张力。根据张力-pCa曲线推断单次收缩过程中肌浆内达到的[游离Ca2+]浓度。对于同一动物物种的机械去膜细胞,通过两种方法推断肌浆内Ca2+从肌浆网(SR)释放过程中达到的[游离Ca2+]浓度:(a)张力-pCa曲线;(b)水母发光蛋白生物发光瞬变的直接校准。与大鼠去膜细胞相比,兔的SR诱导最大Ca2+释放需要更大的SR Ca2+预负荷和更高的[游离Ca2+]触发值。然而,用两种推断肌浆内[游离Ca2+]的方法得到的结果表明,在这两种动物物种中,无论是去膜细胞的SR最佳Ca2+诱导Ca2+释放过程,还是完整细胞的最佳单次收缩过程,肌浆内达到的最大[游离Ca2+]的pCa约为5.40。这远低于肌丝完全激活所需的[游离Ca2+](pCa约为4.90)。