[Passive transport of calcium into plasma membrane fractions of myometrium cells].
The apparent values of intravesicular volume (45 microliter/mg of protein), maximal capacity of adsorbed calcium binding on the inner surface of the vesicles (4.5 nmol/mg of protein) and dissociation constants for the Ca2+-binding site complexes (36 microM) were determined from the analysis of peculiarities of passive transport of 45Ca2+ into cow myometrium sarcolemmal vesicles. The kinetics of passive efflux of ionized Ca2+ from the vesicles is described by a two-phase exponential curve. Dilution of the vesicles with a dilution medium is associated with a rapid efflux of ionized Ca2+ from the intravesicular space resulting in dissociation of the Ca2+-binding site complexes on the inner surface of the vesicles and, correspondingly, in the passage from a rapid to the slow phase of Ca2+ efflux from the vesicles which is limited by the dissociation of the Ca2+-binding site complexes. The values of the apparent rate constants for the transmembrane transfer of Ca2+ and dissociation of the Ca2+-binding site complexes (0.73 and 0.02 min-1, respectively) and the permeability of sarcolemmal vesicles for the cation (10(-15) mol of Ca2+/cm2.s) were determined. Alkalinization of the dilution medium stimulates 45Ca2+ release from the vesicles. The blockers of passive Co2+ and Mn2+ transport injected into the vesicles inhibit the efflux of 45Ca2+ from the vesicles. The data obtained were used to analyze the role of sarcolemma in the Ca2+ control of myometrium contraction.
D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002463:Cell Membrane Permeability; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D009215:Myometrium / Q000378:metabolism*; D012508:Sarcolemma / Q000378:metabolism; D014590:Uterine Contraction
D002118:Calcium
Passivnyĭ transport kal'tsiia vo fraktsii plazmaticheskikh membran kletok miometriia.