The aims of this work were to determine: 1) whether Ca 2+ exit via the plasmalemmal Ca 2+ ATPase (PMCA) is coupled to H + entry via a Ca 2+/H + exchange; 2) whether operation of PMCA has an absolute requirement on external H + (H o); and 3) the stoichiometry and voltagedependence of the Ca 2+/H + exchange. Barnacle muscle cells were used because of the ease with which they can be internally-perfused (e.g., with 45Ca), voltage-clamped and impaled with a pH electrode. Thus, the simultaneous measurement of plasmalemmal Ca 2+ and H + fluxes can be measured. The effects of H o, intracellular ATP, PMCA blockers, and membrane potential (V M) were studied on PMCA-mediated Ca 2+/H + exchange. The results indicate that: i) Ca 2+ efflux is promoted by external acidification, is accompanied by a membrane depolarization, and by an intracellular acidification greater than the one resulting from H o "leak" and PMCA-mediated ATP hydrolysis; ii) H o-dependent Ca 2+ efflux is inhibited by PMCA blockers and by ATP depletion and is accelerated by membrane depolarization (∼3 fold by 20 mV depolarization); iii) the coupling ratio of the Ca 2+/H + exchange depends on Ho: at an extracellular pH (pH o)=6.5, the ratio is 1Ca 2+:∼3H +; at pH o=8.2, Ca 2+ efflux rate is 3 times slower and the ratio is 1Ca 2+:<1H +.
- Ca /H exchange
- Ca ATPase
- Ca buffering
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Immunology and Microbiology(all)