Properties of Ca2+ release-activated Ca2+ channel block by 5-nitro-2-(3-phenylpropylamino)-benzoic acid in Jurkat cells

Ca2+ release-activated Ca2+ 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 (IC50 = 5 mu M). Kinetics for block and unblock of I-crac by NPPB indicated a bimolecular interaction, Michaelis-Menten analysis indicated that NPPB interacts competitively with extracellular Ca2+ 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 Ca2+ release-activated Ca2+ (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. (C) 2000 Elsevier Science B.V. All rights reserved.