The pathway for refilling intracellular Ca2+ stores passes through the cytosol in human leukaemia cells.
The pathway for refilling the intracellular Ca2+ stores of HL60 and U937 human leukaemia cells loaded with fura-2 has been investigated. On addition of external Ca2+ to cells with empty stores there was an increase in the cytosolic Ca2+ concentration ([Ca2+]i) which preceded the refilling of the stores. The increase in [Ca2+]i was faster than the refilling, by 3- to 15-fold, depending on the cell type. In measurements in single HL60 cells we found that the refilling of the stores correlated with the extent of the [Ca2+]i increase on addition of external Ca2+. The cells showing no [Ca2+]i increase were unable to refill their stores. The addition of Ni2+ to the extracellular medium prevented both the [Ca2+]i increase and the refilling of the stores. These results indicate that the limiting step for store refilling is the entry of Ca2+ from the extracellular medium to the cytosol. Hence, we conclude that extracellular Ca2+ cannot gain access directly to the intracellular Ca2+ stores in these cells, but must first enter the cytosol and be taken up from there into the stores.
Montero
M
M
Departamento de Bioquímica y Biología Molecular y Fisiología, Facultad de Medicina, Universidad de Valladolid, Spain.
Alonso-Torre
S R
SR
Alvarez
J
J
Sanchez
A
A
García-Sancho
J
J
D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D016257:Fura-2; D006801:Humans; D007700:Kinetics; D007938:Leukemia; D014407:Tumor Cells, Cultured
D002118:Calcium; D016257:Fura-2