In permeabilized rat hepatocytes a maximal concentration (25 microM) of 2,5-di-(tert-butyl)-1,4-benzohydroquineone (tBuBHQ) mobilized 70% of sequestere Ca2+ and a half-maximal effect was produced by 1.7 microM tBuBHQ. Inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) stimulated release of about 40% of the intracellular Ca2+ stores. Combined applications of a range of tBuBHQ concentrations with a maximal concentration of Ins(1,4,5)P3 demonstrated that tBuBHQ has slight selectivity for the Ca2+ transport process of the Ins(1,4,5)P3-sensitive stores. We conclude that the Ins(1,4,5)P3-sensitive stores are a subset of those sensitive to tBuBHQ and that the latter is therefore unlikely to prove useful as a tool to discriminate Ins(1,4,5)P3-sensitive and -insensitive Ca2+ stores though it may provide opportunities to design more selective agents.
