Sodium-calcium exchange and sidedness of isolated cardiac sarcolemmal vesicles.
The sidedness of isolated rabbit cardiac sarcolemmal vesicles was studied by observing the effects of several permeability-increasing agents on measurements of the amount of sialic acid released by neuraminidase, specific ouabain binding, and K+-phosphatase and (Na+ + K+)-ATPase activities. The results suggest that the vesicles are sealed and are about 80% right-side-out. Na+-Ca2+ exchange exhibited by these vesicles could be attributed to the sarcolemma rather than to some contaminating organelle. Ca2+ uptake was stimulated by preloading the vesicles with NaCl (and not KCl). Increasing the external [Na+] induced a rapid Ca2+ loss, which could not be mimicked by K+, Li+, Rb+ or choline+. The Nai+-dependent Ca2+ uptake was inhibited by certain cations: Cd2+ > La3+ > Y3+ > Mn2+ > Co2+ > Mg2+. The Nai+-dependent Ca2+ influx was enhanced by an inside positive membrane potential and inhibited by an inside negative membrane potential. Potentials were induced by a K+-valinomycin system.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000378:metabolism / Q000648:ultrastructure*; D010042:Ouabain / Q000378:metabolism; D011817:Rabbits; D012508:Sarcolemma / Q000378:metabolism / Q000648:ultrastructure*; D012794:Sialic Acids / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
D012794:Sialic Acids; D010042:Ouabain; D012964:Sodium; D002118:Calcium