Uptake of Ca2+ and refilling of intracellular Ca2+ stores in Ehrlich-ascites-tumour cells and in rat thymocytes.
We have studied the uptake of Ca2+ and its redistribution between the cytoplasm and the intracellular stores in Ehrlich-ascites-tumour cells and rat thymocytes previously depleted of Ca2+ by incubation in Ca2(+)-free medium. Measurements included changes of the cytoplasmic Ca2+ concentration ([Ca2+]i), uptake of 45Ca2+ and uptake of Mn2+, a Ca2+ surrogate for Ca2+ channels. Refilling of the Ca2+ stores in thymocytes was very fast (half-filling time: 4 s at 37 degrees C) and very sensitive to temperature (10 times slower at 20 degrees C). It was always preceded by increase of [Ca2+]i. In the Ehrlich cell, both refilling and increase of [Ca2+]i were about one order of magnitude slower. The increase of [Ca2+]i and the refilling of the intracellular stores were both almost completely blocked by Ni2+ in thymocytes, but only partially in the Ehrlich cell. The rates of 45Ca2+ and Mn2+ uptake varied consistently with temperature and the kind of cell. These results suggest that the intracellular stores are refilled by Ca2+ taken up from the cytoplasm. We also find that filling of the Ca2+ stores decreases by about 90% the rate of Mn2+ uptake in thymocytes. This is direct evidence of modulation of the plasma-membrane Ca2+ entry by the degree of filling of the intracellular stores. This modulation occurs in the absence of agonists, suggesting some kind of signalling between the intracellular stores and the Ca2+ entry pathways of the plasma membrane.
Montero
M
M
Departamento de Bioquímica, Biología Molecular y Fisiología, Facultad de Medicina, Universidad de Valladolid, Spain.
Alvarez
J
J
Garcia-Sancho
J
J
D000634:Aminoquinolines; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D005456:Fluorescent Dyes; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D008345:Manganese / Q000378:metabolism; D009532:Nickel / Q000494:pharmacology; D051381:Rats; D013950:Thymus Gland / Q000187:drug effects / Q000378:metabolism*
D000634:Aminoquinolines; D005456:Fluorescent Dyes; D008345:Manganese; D004533:Egtazic Acid; D015759:Ionomycin; D009532:Nickel; C035739:Quin2; D002118:Calcium