DEPLETION OF INTRACELLULAR CA2+ STORES ACTIVATES A CA2+-SELECTIVE CHANNEL IN VASCULAR ENDOTHELIUM

The present study was designed to identify the channel responsible for Ca2+ influx after depletion of intracellular Ca2+ stores. Different maneuvers that deplete intracellular Ca2+ stores activated a Ca2+-selective channel. Superfusion of single bovine aortic endothelial cells with 50 nmol/l bradykinin, 10 mu mol/l ATP, or 10 mu mol/l 2,5-di(tert-butyl)-1,4-benzohydroquinone produced activation of channels of the same amplitude in cell-attached patches. Channel activity declined within the first minute after patch excision. The channel showed strong inward rectification and a reversal potential of 0 mV in symmetrical sodium sulfate (Na2SO4) solution. Under these conditions, the conductance was 5 pS in the inward direction. Addition of 10 mmol/l Ca2+ to the extracellular solution shifted the reversal potential to +30 +/- 5 mV, and the conductance for inward current was 11 pS. The reversal potential was used to calculate an ion permeability ratio of Ca2+/Na+ > 10:1.