Casteels R, Raeymaekers L, Droogmans G, Wuytack F
J Cardiovasc Pharmacol. 1985;7 Suppl 3:S103-10.
The evidence in favor of a direct role of active Na transport in the regulation of excitation-contraction coupling in vascular smooth muscle has been examined. The observations in vivo and those obtained in isolated tissues do not always lead to the same conclusions. The changes of the membrane potential obtained in vitro by slight reductions in, or increases of [K]o do not modify the resting potential of the cells sufficiently to make them contract. Applying K-free or Na-free medium on isolated tissues is a much more vigorous procedure than the limited changes of [K]o that can occur in vascular beds in situ. The Na-Ca exchange-mechanism does not seem to play a major role in those smooth-muscle cells that have been analyzed in detail, but even here the experimental procedures have neither given precise information about the composition of the intracellular compartment nor allowed sufficient control of the parameters studied. The comparison of membrane vesicles from smooth muscle and from cardiac muscle indicates that important differences exist in Na-Ca exchange and in activities of Na+-K+ ATPase and Ca2+-Mg2+ ATPase. These findings suggest a poor development of Na-Ca exchange in smooth muscle as compared to cardiac muscle. Finally, the changes in the Na metabolism of erythrocytes from hypertensives are mentioned, and the present difficulties of linking those changes to an increased reactivity of vascular smooth-muscle cells are briefly discussed.
关于主动钠转运在血管平滑肌兴奋 - 收缩偶联调节中直接作用的证据已被研究。体内观察结果与在分离组织中获得的结果并不总是得出相同的结论。在体外通过轻微降低或增加[K]o所获得的膜电位变化，不足以充分改变细胞的静息电位使其收缩。在分离组织上应用无钾或无钠培养基比血管床原位可能发生的[K]o有限变化要剧烈得多。钠 - 钙交换机制在那些已被详细分析的平滑肌细胞中似乎并不起主要作用，但即便如此，实验程序既未给出关于细胞内区室组成的精确信息，也未对所研究的参数进行充分控制。平滑肌和心肌膜囊泡的比较表明，钠 - 钙交换以及钠 - 钾ATP酶和钙 - 镁ATP酶的活性存在重要差异。这些发现表明，与心肌相比，平滑肌中钠 - 钙交换发育较差。最后，提到了高血压患者红细胞钠代谢的变化，并简要讨论了目前将这些变化与血管平滑肌细胞反应性增加联系起来的困难。
