title: Calcium-ion transport by intact Ehrlich ascites-tumour cells. Role of respiratory substrates, Pi and temperature.
abstract: 1. The interaction of intact Ehrlich ascites-tumour cells with Ca2+ at 37 degrees C consists of Ca2+ uptake followed by efflux from the cells. Under optimum conditions, two or three cycles of uptake and efflux are observed in the first 15 min after Ca2+ addition. 2. The respiratory substrates malate, succinate and ascorbate plus p-phenylenediamine support Ca2+ uptake. Ca2+ uptake at 37 degrees C is sensitive to the respiratory inhibitors rotenone and antimycin A when appropriate substrates are present. Ca2+ uptake and retention are inhibited by the uncoupler S-13. 3. Increasing extracellular Pi (12 to 30 mM) stimulates uncoupler-sensitive Ca2+ uptake, which reaches a maximum extent of 15 nmol/mg of protein when supported by succinate respiration. Ca2+ efflux is partially inhibited at 30 mM-Pi. 4. Optimum Ca2+ uptake occurs in the presence of succinate and Pi, suggesting that availability of substrate and Pi are rate-limiting. K. Ca2+ uptake occurs at 4 degrees C and is sensitive to uncouplers and oligomycin. Ca2+ efflux at this temperature is minimal. These data are consistent with a model in which passive diffusion of Ca2+ through the plasma membrane is followed by active uptake by the mitochondria. Ca2+ uptake is supported by substrates entering respiration at all three energy-coupling sites. Ca2+ efflux appears to be an active process with a high temperature coefficient.
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism*; D004734:Energy Metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008314:Malonates / Q000494:pharmacology; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D009840:Oligomycins / Q000494:pharmacology; D010710:Phosphates / Q000494:pharmacology; D013386:Succinates / Q000378:metabolism; D013696:Temperature; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D008314:Malonates; D009840:Oligomycins; D010710:Phosphates; D013386:Succinates; D014475:Uncoupling Agents; D001205:Ascorbic Acid; D002118:Calcium