INHIBITION OF CAPACITATIVE CA2+ ENTRY BY A CL- CHANNEL BLOCKER IN HUMAN ENDOTHELIAL-CELLS

We have used the patch clamp technique in combination with intracellular calcium measurements to measure simultaneously Ca2+ entry and ionic currents activated by emptying of intracellular Ca2+ stores (capacitative Ca2+ entry and Ca2+ release-activated Ca2+ currents, CRAC) in human endothelial cells from umbilical veins. Intracellular stores were depleted of Ca2+ by preincubating endothelial cells for 20 minutes with 2 mu M thapsigargin in Ca2+-free solution. Reapplication of 10 mM [Ca2+](e) evoked an increase in [Ca2+](i) indicating Ca2+ influx after the thapsigargin-induced store depletion (capacitative Ca2+ entry), however no measurable CRAC could be detected. The increase in [Ca2+](i) after [Ca2+](e) resubmission was substantially reduced in the presence of 50 mu M NPPB (5-nitro-2-(3-phenylpropylamino)-benzoic acid) from 0.77 +/- 0.25 mu M to 0.2 +/- 0.06 mu M (n = 6) at a holding potential of -40 mV. Estimates of the capacitative Ca2+ entry at various membrane potentials from the first time derivative of the Ca2+ transients showed a highly inwardly rectifying I-V curve with a Ca2+ inward current amplitude of 1.0 +/- 0.3 pA (membrane capacitance 59 +/- 9 pF, n = 8) at -80 mV. This current amplitude was decreased to 0.32 +/- 0.12 pA (n = 6) in the presence of 50 mu M NPPB. This corresponds to a decrease in the Ca2+ permeability of the endothelial cell membrane from 0.15 . 10(-8) cm/s (control) to 0.06 . 10(-8) cm/s (50 mu M NPPB).