2-Aminoethoxydiphenyl borate (2-APB) antagonises inositol 1,4,5-trisphosphate-induced calcium release, inhibits calcium pumps and has a use-dependent and slowly reversible action on store-operated calcium entry channels

The action of 2-aminoethoxydiphenyl borate (2-APB) on Ca²⁺ signalling in HeLa cells and cardiac myocytes was investigated. Consistent with other studies, we found that superfusion of cells with 2-APB rapidly inhibited inositol 1,4,5-trisphosphate (InsP₃ -mediated Ca²⁺ release and store-operated Ca²⁺ entry (SOC). In addition to abrogating hormone-evoked Ca²⁺ responses, 2-APB could antagonise Ca²⁺ signals evoked by a membrane permeant InsP₃ ester. 2-APB also slowed the recovery of intracellular Ca²⁺ signals consistent with an effect on Ca²⁺ ATPases. The inhibitory action of 2-APB on InsP₃ receptors (InsP₃Rs), SOC channels and Ca²⁺ pumps persisted for several minutes after washout of the compound. Application of 2-APB to unstimulated cells had no effect on subsequent Ca²⁺ responses suggesting that it has a use-dependent action. Mitochondria in cells treated with 2-APB showed a rapid and slowly reversible swelling. 2-APB did not cause the mitochondria to depolarise, but it reduced the extent of mitochondrial calcium uptake. Although 2-APB has been demonstrated not to affect voltage-operated Ca²⁺ channels or ryanodine receptors, we found that it gave a concentration-dependent long-lasting inhibition of Ca²⁺ signalling in electrically-stimulated cardiac myocytes, where InsP₃Rs and SOC channels do not play a significant role. Our data suggest that 2-APB has multiple cellular targets, a use-dependent action, is difficult to reverse and may affect Ca²⁺ signalling in cell types where InsP₃ and SOC are not active.