Membrane depolarization selectively inhibits receptor-operated calcium channels in human T (Jurkat) lymphoblasts

Jurkat lymphoblasts were stimulated by a monoclonal antibody against the CD3 membrane antigen and the evoked calcium signal was followed by the intracellular fluorescent calcium indicator indo-1. The technique applied allowed us to separately investigate the stimulus-induced intracellular calcium release and the calcium-influx pathways, respectively. In the same cells membrane potential was estimated by the fluorescent dye diS-C3-(5). The resting membrane potential of Jurkat lymphoblasts under normal conditions was between -55 and -60 mV. Membrane depolarization, obtained by increasing external K+ concentration, removing external Cl-, or by increasing the Na+/K+ leak permeability with gramicidin or PCMBS, did not induce calcium influx in the resting cells and did not influence the CD3 receptor-mediated internal calcium release, while strongly inhibited the receptor-mediated calcium influx pathway. Half-maximum inhibition of this calcium influx was observed at membrane potential values of about -35 to -40 mV and this inhibition did not depend on the external calcium concentration varied between 5 and 2500 microM. Membrane hyperpolarization by valinomycin did not affect either component of the calcium signal. The observed selective inhibition of the receptor-operated calcium influx pathway by membrane depolarization is probably an important modulator of calcium-dependent cell stimulation.