2APB, 2-AMINOETHOXYDIPHENYL BORATE, A MEMBRANE-PENETRABLE MODULATOR OF INS(1,4,5)P-3-INDUCED CA2+ RELEASE

The effects of a novel membrane-penetrable modulator, 2APB (2-aminoeth oxy diphenyl berate), on Ins(1,4,5)P-3-induced Ca2+ release were exami ned. 2APB inhibited Ins(1,4,5)P-3-induced Ca2+ release from rat cerebe llar microsomal preparations without affecting [H-3]Ins(1,4,5)P-3 bind ing to its receptor. The IC50 value (concentration producing 50% inhib ition) of 2APB for inhibition of Ins(1,4,5)P-3 (100 nM) induced Ca2+ r elease was 42 mu M Further increase in the concentration of 2APB (more than 90 mu M) caused a gradual release of Ca2+ from cerebellar micros omal preparations. Addition of 2APB to the extracellular environment i nhibited the cytosolic Ca2+ ([Ca2+](c)) rise in intact cells such as h uman platelets and neutrophils stimulated by thromboxane-mimetic STA(2 ) or thrombin, and leukotriene B-4 (LTB4) or formyl-methionine-leucine -phenylalanine (FMLP), respectively. 2APB inhibited the contraction of thoracic aorta isolated from rabbits induced by angiotensin II (AII), STA(2), and norepinephrine in a non-competitive manner, but showed no effect on the contraction of potassium-depolarized muscle. 2APB had n o effect on the Ca2+ release from the ryanodine-sensitive Ca2+ store p repared from rat leg skeletal muscle and heart. Although the specifici ty of 2APB with respect to the intracellular signaling system was not fully established, 2APB is the first candidate for a membrane-penetrab le modulator of Ins(1,4,5)P-3 receptor, and it should be a useful tool to investigate the physiological role of the Ins(1,4,5)P-3 receptor i n various cells.