Chapman R A, Coray A, McGuigan J A
J Physiol. 1983 Oct;343:253-76. doi: 10.1113/jphysiol.1983.sp014891.
A method for mounting and rapidly perfusing small ventricular trabeculae (diameter around 250 micron) from either ferret or guinea-pig is described. Tension, membrane potential (Em) and intracellular Na activity (aiNa) were measured. aiNa was measured using Na-sensitive micro-electrodes. At room temperature (22-26 degrees C), [Na]o 155 mmol/l and [Ca]o 5.4 mmol/l, aiNa was 10.9 mmol/l +/- S.D. 4.2 mmol/l (n = 148). When [Na]o was reduced from 155 to 1.5 mmol/l contractures developed. These were about twitch height in guinea-pig but less than the twitch height in ferret. Associated with the development of the contracture there was a decrease in aiNa. The aiNa halved within 30 s. The decrease in aiNa was not influenced by changing pHo from 7.4 to 9.5, K-free solution or strophanthidin 50 mumol/l and was not passive since, even when the [Na]o was 1.5 mmol/l, the driving force for Na ions remained inward. The aiNa decreased if [Ca]o was increased and [Na]o decreased or vice versa. On the basis of these findings it is concluded that the decrease in aiNa is mainly due to Na/Ca exchange. Despite the large decrease in aiNa the [Ca]i, as monitored by tension changes, hardly increased. Since Ca uptake does occur in Na-free conditions in heart muscle it is proposed that the mitochondria take up Ca ions and so prevent an excessive rise in cytoplasmic Ca. Strophanthidin increased both aiNa and the withdrawal contracture, but collected results from a number of experiments showed no clear correlation between the initial aiNa and contracture amplitude. Strophanthidin may, therefore, have actions additional to increasing aiNa.
本文描述了一种用于安装并快速灌注雪貂或豚鼠小室小梁（直径约250微米）的方法。测量了张力、膜电位（Em）和细胞内钠活性（aiNa）。使用钠敏感微电极测量aiNa。在室温（22 - 26摄氏度）、细胞外钠浓度（[Na]o）为155 mmol/L和细胞外钙浓度（[Ca]o）为5.4 mmol/L时，aiNa为10.9 mmol/L ± 标准差4.2 mmol/L（n = 148）。当[Na]o从155 mmol/L降至1.5 mmol/L时，出现挛缩。在豚鼠中，这些挛缩约为抽搐高度，但在雪貂中小于抽搐高度。随着挛缩的发展，aiNa降低。aiNa在30秒内减半。aiNa的降低不受细胞外pH值从7.4变为9.5、无钾溶液或50 μmol/L毒毛花苷的影响，并且不是被动的，因为即使[Na]o为1.5 mmol/L时，钠离子的驱动力仍向内。如果[Ca]o增加而[Na]o降低，或者反之，则aiNa降低。基于这些发现得出结论，aiNa的降低主要是由于钠/钙交换。尽管aiNa大幅降低，但通过张力变化监测的细胞内钙浓度（[Ca]i）几乎没有增加。由于在心肌无钠条件下确实发生钙摄取，因此提出线粒体摄取钙离子，从而防止细胞质钙过度升高。毒毛花苷增加了aiNa和舒张期挛缩，但多个实验收集的结果表明，初始aiNa与挛缩幅度之间没有明显相关性。因此，毒毛花苷可能除了增加aiNa之外还有其他作用。
