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  • Title: Sodium-calcium exchange and sidedness of isolated cardiac sarcolemmal vesicles.
    Author: Bers DM, Philipson KD, Nishimoto AY.
    Journal: Biochim Biophys Acta; 1980 Sep 18; 601(2):358-71. PubMed ID: 7407175.
    Abstract:
    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.
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