2-Aminoethoxydiphenyl borate affects the inositol 1,4,5-trisphosphate receptor, the intracellular Ca2+ pump and the non-specific Ca2+ leak from the non-mitochondrial Ca2+ stores in permeabilized A7r5 cells
2-Aminoethoxydiphenyl borate (2APB) is a membrane-permeable blocker of the inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release in bi-directional Ca2+ -flux conditions. We have now studied the effects of 2APB on the 45Ca2+ uptake into, and on the basal and IP(3)-stimulated unidirectional 45Ca2+ efflux from the non-mitochondrial Ca2+ stores in permeabilized A7r5 smooth-muscle cells. 2APB inhibited the IP3 -induced Ca2+ release, with a half maximal inhibition at 36 microM 2APB, without affecting [3H]IP3 binding to the receptor. This inhibition did not depend on the IP3, ATP or free Ca2+ concentration. The Ca2+ pumps of the non-mitochondrial Ca2+ stores were half-maximally inhibited at 91microM 2APB. Higher concentrations of 2APB increased the non-specific leak of Ca2+ from the stores. We conclude that 2APB can not be considered as a selective blocker of the IP3 -induced Ca2+ release. Our results can explain the various effects of 2APB observed in intact cells.