Properties of Ca(2+) release-activated Ca(2+) channel block by 5-nitro-2-(3-phenylpropylamino)-benzoic acid in Jurkat cells

Abstract

Ca(2+) release-activated Ca(2+) current (I(crac)) has been previously characterized biophysically in Jurkat lymphocytes and other non-excitable cells, but pharmacology remains poorly developed. The present objective was to delineate with whole cell recording details of the interaction of the chloride channel blocker, 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), with I(crac) in Jurkat cells. NPPB reversibly inhibited I(crac) in a concentration-dependent manner (IC(50)=5 microM). Kinetics for block and unblock of I(crac) by NPPB indicated a bimolecular interaction. Michaelis-Menten analysis indicated that NPPB interacts competitively with extracellular Ca(2+) permeating the I(crac) pathway. Finally, analysis of the pH dependence of I(crac) block by NPPB revealed a reduction in the apparent affinity during extracellular alkalinization that based on the pK(a) for NPPB, suggested that the neutral form of NPPB blocks the Ca(2+) release-activated Ca(2+) (CRAC) channel. Taken together, our results suggest a direct interaction between NPPB and the CRAC channel, and should help guide insights for developing novel and more selective analogues.