Interdependence of H+ and K+ fluxes during the Ca(2+)-pumping activity of sarcoplasmic reticulum vesicles.
The release of H+ during the oxalate-supported Ca2+ uptake in sarcoplasmic reticulum vesicles is kinetically coincident with the initial phase of Ca2+ accumulation. The Ca2+ uptake is increased and the H+ release is decreased in the presence of KCl and other monovalent chloride salts as expected for a H(+)-monovalent cation exchange. The functioning of the Ca(2+)-pump is disturbed by the presence of potassium gluconate and to a lesser extent, of choline chloride. These salts do not inhibit the ATPase activity of Ca(2+)-permeable vesicles, suggesting a charge imbalance inhibition which is specially relevant in the case of gluconate. Therefore, K+, and also Cl-, appear to be involved in secondary fluxes during the active accumulation of Ca2+. The microsomal preparation seems homogeneous with respect to the K(+)-channel, showing an apparent rate constant for K+ release of approximately 25 s-1 measured with the aid of 86Rb+ tracer under equilibrium conditions. A Rb+ efflux, sensitive to Ca(2+)-ionophore, can be also detected during the active accumulation of Ca2+. The experimental data suggest that both monovalent cations and anions are involved in a charge compensation during the Ca2+ uptake and H+ release. Fluxes of these highly permeable ions would contribute to cancel the formation of a resting membrane potential through the sarcoplasmic reticulum membrane.
Soler
F
F
Departamento de Bioquimica y Biologia Molecular, Facultad de Veterinaria, Universidad de Murcia, Spain.
Sanchez-Migallon
P
P
Gomez-Fernandez
J C
JC
Fernandez-Belda
F
F
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000187:drug effects / Q000378:metabolism*; D002794:Choline / Q000378:metabolism; D005942:Gluconates / Q000494:pharmacology; D006859:Hydrogen / Q000378:metabolism*; D066298:In Vitro Techniques; D007474:Ion Exchange; D007700:Kinetics; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D005942:Gluconates; D006859:Hydrogen; D000252:Calcium-Transporting ATPases; D002794:Choline; C030691:gluconic acid; D011188:Potassium; D002118:Calcium