Stoichiometry of the sodium-calcium exchanger in nerve terminals.
The stoichiometry of the Na+-Ca2+ exchanger from synaptic plasma membranes was studied in both native and reconstituted preparations. In kinetic experiments performed with the native preparation, initial rates of Na+ gradient-dependent Ca2+ influx were compared to Ca2+-dependent Na+ efflux. These experiments showed that 4.82 Na+ ions are exchanged for each Ca2+ ion. A thermodynamic approach in which equilibrium measurements were made with the reconstituted preparation resulted in a similar (4.76) stoichiometry. The effects of membrane potential generated by valinomycin-induced K+ fluxes could be demonstrated in the reconstituted preparation. In addition, the direct contribution of the Na+-Ca2+ exchanger to the membrane potential across the reconstituted vesicle membrane could be demonstrated by using the lipophilic cation tetraphenylphosphonium.
Barzilai
A
A
Department of Biochemistry, Hebrew University, Hadassah Medical School, Jerusalem, Israel.
Rahamimoff
H
H
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002794:Choline / Q000494:pharmacology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D012964:Sodium / Q000378:metabolism; D012979:Sodium Radioisotopes; D019831:Sodium-Calcium Exchanger; D013570:Synaptic Membranes / Q000378:metabolism* / Q000502:physiology
D002352:Carrier Proteins; D012979:Sodium Radioisotopes; D019831:Sodium-Calcium Exchanger; D012964:Sodium; D002794:Choline; D002118:Calcium