A role of H+ flux in active Ca2+ transport into sarcoplasmic reticulum vesicles. II. H+ ejection during Ca2+ uptake.
Proton efflux during Ca2+ transport into sarcoplasmic reticulum vesicles was examined. Although a rapid H+ ejection was observed during the initial phase of Ca2+ uptake and the amount of the liberated H+ was more than that due to hydrolysis of ATP, generation of a pH difference as a result of the H+ efflux could not be detected by direct pH measurement with a pH meter. Alkalinization of the inside of the vesicles during Ca2+ uptake was more precisely examined by flow dialysis assay and a significant uptake of acetate or salicylate into the vesicles was found, suggesting the generation of a small pH difference across the SR membrane. From these results, it was concluded that counter-transport of H+ was operative in Ca2+ uptake but that only a relatively small pH difference was generated as a result of the H+ efflux. The intrinsic buffering capacity of sarcoplasmic reticulum vesicles was measured and a relatively large value (130 nmol H+/pH unit/mg at pH 6.2) was obtained.
D000818:Animals; D001693:Biological Transport, Active; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D003956:Dialysis; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D011522:Protons; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D014634:Valinomycin / Q000494:pharmacology
D011522:Protons; D014634:Valinomycin; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D000001:Calcimycin; D006859:Hydrogen; D002118:Calcium