[Active Na+-dependent transport of Ca 2+ into the fraction of smooth muscle sarcolemma vesicles].
Studies on the vesicular fraction of myometrium sarcolemma showed that in the absence of initial Ca2+ gradient the vesicles activity accumulate Ca2+ by utilizing the energy of the antiport-directed Na+ gradient. Monensin (50 microM) suppresses practically completely the Ca2+ transport. The amount of Ca2+ entering the vesicles against the concentration gradient diminishes with a decrease in the oppositely directed Na+ gradient. Cd2+ (5 mM) causes a complete inhibition of active Ca2+ transport, whereas Mn2+ and Mg2+ inhibit this process by 85% and 35%, respectively; amiloride (500 microM) is fairly ineffective. In the absence of initial Ca2+ and Na+ gradients valinomycin (0.05-1 microM) does not affect the changes in Ca2+ concentration in the intravesicular volume both with and without K+ gradient. Under conditions of initial equilibrium for Ca2+ and Na+ the magnitude and sign of the membrane potential for the K(+)-valinomycin system have no effect on Ca2+ transport regardless of value of absolute Na+ concentration inside and outside the vesicles. Depolarization of membrane vesicles does not interfere with the Na(+)-driven active Ca2+ transport into the sarcolemma which is dependent on the energy of the Na+ gradient. Using calibration curves, it was shown that the physiologically significant (6-fold) Na+ gradient increases Ca2+ concentration in the intravesicular volume from 100 to 160-170 microM. Ac active potential-independent Ca2+ transport through the smooth muscle sarcolemma requires about one third (0.3 kcal/mol) of the Na+ gradient; energy the remainder is dissipated. It is concluded that in smooth muscles the Na+ gradient can provide the active transsarcolemmal transport of Ca2+.
Burchinskaia
N F
NF
Shlykov
S G
SG
Kosterin
S A
SA
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000502:physiology*; D013552:Swine
D000584:Amiloride; D012964:Sodium; D002118:Calcium
Aktivnyĭ Na+-zavisimyĭ transport Ca 2+ vo fraktsii vezikul sarkolemmygladkoĭ myshtsy.