Effects of sulfhydryl reagents on Na+-Ca2+ exchange in rat brain microsomal membranes.
Effects of six thiol reagents with different physico-chemical properties were tested on the Na+-dependent 45Ca2+ transport into the rat brain microsomal membrane vesicles. The mercurials p-chlormercuribenzoate and Mersalyl effectively inhibited 45Ca2+ uptake with IC50 values in the order of 10(-4) mol X l-1 in the medium. N-ethylmaleimide and its more lipophilic analog N-(4-(2-benzoxazolyl)phenyl)maleimide were much less effective at the same concentrations. 2,2'-dithiodipyridine markedly reduced 45Ca2+ uptake already at concentrations below 10(-4) mol X l-1, whereas 5,5'-dithiobis-2-nitrobenzoate in a concentration range 10(-6)-10(-3) mol X l-1 was a weak inhibitor. Inhibitory effects of the most potent inhibitors p-chlormercuribenzoate and 2,2'-dithiodipyridine were readily reversed by 1 mmol X l-1 dithiothreitol. The results suggest that free SH groups of membrane polypeptides are involved in the functioning of the Na+-Ca2+ exchanger in the nerve tissue cell membranes.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D007474:Ion Exchange; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger; D013439:Sulfhydryl Reagents / Q000494:pharmacology*
D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D013439:Sulfhydryl Reagents; D012964:Sodium; D002118:Calcium