Abstract
Vesicles derived from the plasma membrane of bovine heart muscle catalyze an uptake of 45Ca+ which is dependent on Na+ inside the vesicles and inhibited by external Na+ (Ki = 14 mM). The transporter was solubilized with 2% cholate at high ionic strength (0.5 M NaCl) in the presence of 2.4% soybean phospholipids. Appropriate dilution and sedimentation yielded a preparation of the transporter which could be reconstituted into liposomes. The proteoliposomes catalyzed Ca2+ uptake with a specific activity about 5 times higher than native vesicles. External Na+ inhibited Ca2+ uptake with a Ki of 50 mM. The uptake of Ca2+ was also inhibited when the Na+ gradient was collapsed with nigericin. Ca2+ uptake was stimulated when either valinomycin or dinitrophenol was added to the assay, in line with the known electrogenic nature of the transport system.
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