[Effect of the membrane potential on the passive transport of Ca2+ in fractions of vesicles of the myometrium sarcolemma].
Using a potential-sensitive fluorescent probe diS-C3-(5), the formation of the membrane (K+-diffusion) potential, delta psi, in the myometrium sarcolemmal vesicular fraction was demonstrated. The magnitude of this potential corresponds to that calculated according to the Nernst equation, is time-stable (characteristic dissociation time--3-5 min) and temperature-dependent and is generated upon the substitution of the anion (Cl- for gluconate-) and the compensating cation (Na+ for Tris+, choline+). The change in delta psi from -61 to 0 mV leads to the activation of passive Ca2+ efflux from the vesicles (with choline+ as the compensating cation in the dilution medium). At the same value of the potential, i. e., -61 mV, the substitution of choline in the dilution medium for Na+ or Li+ stimulates the passive release of Ca2+. Co2+, Mn2+ and D-600 suppress this process by 15-20% in depolarized vesicles which points to the inhibition of Ca2+ release with an alteration of the membrane potential value from 0 to -61 mV (20%). The potential-dependent component of passive Ca2+ transport is characterized by saturation with the substrate (Km = 0.5 mM). The dependence of Ca2+ flux release from the sarcolemmal vesicles on the membrane potential value (-60-+27 mV) is bell-shaped and qualitatively relative to the volt-amper characteristics of the steady state Ca2+ flux in single smooth muscle cells. Analysis of experimental results revealed that the potential-dependent component of passive Ca2+ transport in myometrium sarcolemmal vesicles is determined by the non-activated Ca2+ conductivity of plasma membrane.
D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D005260:Female; D007473:Ion Channels / Q000378:metabolism*; D008564:Membrane Potentials; D009215:Myometrium / Q000378:metabolism* / Q000502:physiology; D012508:Sarcolemma / Q000378:metabolism* / Q000502:physiology
D007473:Ion Channels; D002118:Calcium
Vliianie membrannogo potentsiala na passivnyĭ transport Ca2+ vo fraktsii vezikul sarkolemmy miometriia.