Abstract

Regulation of the kinetics of intracellular Ca²⁺ signals with a novel, membrane-penetrable, inositol 1,4,5-trisphosphate (InsP₃) receptor/Ca²⁺ channel modulator, 2-amino-ethoxydiphenyl borate (2APB), has been investigated using patch-clamp, whole-cell recording to monitor Ca²⁺-activated Cl⁻ currents in single isolated pancreatic acinar cells. 2APB itself fails to evoke a detectable current response but it dramatically changes the kinetics of agonist-induced Ca²⁺release from pulsatile spikes to long-lasting, huge Ca²⁺waves, suggesting that 2APB coordinates local Ca²⁺ release to generate global Ca²⁺ signals. The regulation by 2APB can be elicited by internal perfusion of InsP₃ in a concentration-dependent manner, indicating that this regulation is not mediated through membrane receptors or G protein signal transduction. The InsP₃ receptor blocker heparin, but not the ryanodine-sensitive receptor blockers ruthenium red or ryanodine, abolishes 2APB-mediated regulation of Ca²⁺ release. This results also suggest that 2APB effects are mediated through InsP₃ receptors. 2APB substantially modifies single inward Cl⁻ current pulse evoked by the photolytic release of caged InsP₃ but not by caged Ca²⁺. These data indicate that 2APB-induced regulation is mediated neither by Ca²⁺-induced Ca²⁺ release nor by affecting Cl⁻ channel activity directly. We conclude that 2APB regulates the kinetics of intracellular Ca²⁺ signals, represented as the change in the Ca²⁺ oscillation patterns from brief pulsatile spikes to huge, long-lasting Ca²⁺waves. Moreover, this regulation seems to be mediated through InsP₃-sensitive Ca²⁺ pools. 2APB may act as a novel, useful pharmacological tool to study the genesis of intracellular Ca²⁺ signals.