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 C a2+-flux conditions. We have now studied the effects of 2APB on the Ca-45(2 +) uptake into, and on the basal and IP3-stimulated unidirectional Ca-45(2) efflux from the non-mitochondrial Ca2+ stores in permeabilized A7r5 smoot h-muscle cells. 2APB inhibited the IP3-induced Ca2+ release, with a half ma ximal inhibition at 36 muM 2APB, without affecting [H-3]IP, binding to the receptor. This inhibition did not depend on the IP3, ATP or free Ca2+ conce ntration. The Ca2+ pumps of the non-mitochondrial Ca2+ stores were half-max imally inhibited at 91 muM 2APB. Higher concentrations of 2APB increased th e 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 r esults can explain the various effects of 2APB observed in intact cells. (C ) 2001 Harcourt Publishers Ltd.