Asymmetric effects of divalent cations and protons on active Ca2+ efflux and Ca2+-ATPase in intact red blood cells

Journal Article · Sat Oct 01 04:00:00 EDT 1988 · J. Membr. Biol.; (United States)

DOI:https://doi.org/10.1007/BF02009168· OSTI ID:6459115

Xu, Y H; Roufogalis, B D

The influence of the asymmetric addition of various divalent cations and protons on the properties of active Ca2+ transport have been examined in intact human red blood cells. Active Ca2+ efflux was determined from the initial rate of 45Ca2+ loss after CoCl2 was added to block Ca2+ loading via the ionophore A23187. Ca2+-ATPase activity was measured as phosphate production over 5 min in cells equilibrated with EGTA-buffered free Ca2+ in the presence of A23187. The apparent Ca affinity of active Ca2+ efflux (K0.5 = 30-40 mumol/liter cells) was significantly lower than that measured by the Ca2+-ATPase assay (K0.5 = 0.4 microM). Possible reasons for this apparent difference are considered. Both active Ca2+ efflux and Ca2+-ATPase activity were reduced to less than 5% of maximal levels (20 mmol/liter cells.hr) in Mg2+-depleted cells, and completely restored by reintroduction of intracellular Mg2+. Active Ca2+ efflux was inhibited almost completely by raising external CaCl2 (but not MgCl2) to 20 mM, probably by interaction of Ca2+ at the externally oriented E2P conformation of the pump. Cd2+ was more potent than Ca2+ in this inhibition, while Mn2+ was less potent and 10 mM Ba2+ was without effect. A Ca2+: proton exchange mechanism for active Ca2+ efflux was supported by the results, as external protons (pH 6-6.5) stimulated active Ca2+ efflux at least twofold above the efflux rate at pH 7.8 Ca2+ transport was not affected by decreasing the membrane potential across the red cell.

• Research Organization: Univ. of Sydney, New South Wales (Australia)
• OSTI ID: 6459115
• Journal Information: J. Membr. Biol.; (United States), Journal Name: J. Membr. Biol.; (United States) Vol. 105:2; ISSN JMBBB
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ACID ANHYDRASES
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
ANIMALS
ATP-ASE
BARIUM COMPOUNDS
BARYONS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOLOGICAL EFFECTS
BIOLOGICAL MATERIALS
BLOOD
BLOOD CELLS
BODY FLUIDS
CADMIUM COMPOUNDS
CALCIUM 45
CALCIUM COMPOUNDS
CALCIUM ISOTOPES
CATIONS
CHARGED PARTICLES
COBALT COMPOUNDS
DAYS LIVING RADIOISOTOPES
ELEMENTARY PARTICLES
ENZYME ACTIVITY
ENZYMES
ERYTHROCYTES
EVEN-ODD NUCLEI
FERMIONS
HADRONS
HYDROLASES
INTERMEDIATE MASS NUCLEI
IONS
ISOTOPE APPLICATIONS
ISOTOPES
MAGNESIUM COMPOUNDS
MAMMALS
MAN
MANGANESE COMPOUNDS
MATERIALS
MEMBRANE TRANSPORT
NUCLEI
NUCLEONS
PHOSPHOHYDROLASES
PRIMATES
PROTONS
RADIOISOTOPES
TRACER TECHNIQUES
TRANSITION ELEMENT COMPOUNDS
VALENCE
VERTEBRATES