Hazama S
Hokkaido Igaku Zasshi. 1983 Jul;58(4):354-62.
Using a sarcolemmal vesicle-enriched preparation prepared from canine ventricles, the effects of several sulfhydryl reagents on the Na+-Ca2+ exchange were examined. N-Ethylmaleimide (NEM) significantly inhibited the intravesicular Na+ (Na+i)-dependent Ca2+ uptake but did not remarkably affect the extravesicular Na+ (Na+o)-dependent Ca2+ efflux. Iodoacetamide (IAM) had no significant effect on the Na+i-dependent Ca2+ uptake and somewhat promoted the Na+o-dependent Ca2+ efflux. Dithiothreitol (DTT) did not significantly influence the Ca2+ uptake, was inclined to increase passive Ca2+ efflux and apparently decreased the Ca2+ efflux. DTT added with IAM exhibited a significant depressant effect on the Ca2+ uptake and simultaneously had a remarkable increasing effect on passive Ca2+ efflux. NEM and (DTT + IAM), however, did not significantly alter the Km value for Ca2+. p-Chloromercuribenzoate (PCMB) remarkably inhibited the Na+i-dependent Ca2+ uptake but simultaneously showed a remarkable promoting effect on passive Ca2+ efflux, whereby the Na+o-dependent Ca2+ efflux was factually counteracted. These results suggest the possibility that the direction of the Na+-Ca2+ exchange might be controlled by a modification with NEM and IAM of the thiol group(s) in the protein involved in the Na+-Ca2+ counter-transport and that the reductive cleavage of disulfide bond(s) and a modification with PCMB of thiol group(s) present in the sarcolemmal vesicle-associated protein(s) result in an increased Ca2+ permeability in the vesicular membrane.
利用从犬心室制备的富含肌膜囊泡的制剂，研究了几种巯基试剂对钠钙交换的影响。N-乙基马来酰亚胺（NEM）显著抑制囊泡内钠离子（Na+i）依赖性钙摄取，但对囊泡外钠离子（Na+o）依赖性钙外流影响不显著。碘乙酰胺（IAM）对Na+i依赖性钙摄取无显著影响，且在一定程度上促进了Na+o依赖性钙外流。二硫苏糖醇（DTT）对钙摄取无显著影响，倾向于增加被动钙外流，且明显降低了钙外流。DTT与IAM共同添加时，对钙摄取表现出显著的抑制作用，同时对被动钙外流有显著的增加作用。然而，NEM和（DTT + IAM）对钙的米氏常数（Km）值无显著改变。对氯汞苯甲酸（PCMB）显著抑制Na+i依赖性钙摄取，但同时对被动钙外流有显著的促进作用，从而实际上抵消了Na+o依赖性钙外流。这些结果表明，钠钙交换的方向可能通过NEM和IAM对参与钠钙逆向转运的蛋白质中巯基的修饰来控制，并且肌膜囊泡相关蛋白质中存在的二硫键的还原断裂和PCMB对巯基的修饰导致囊泡膜中钙通透性增加。
