INDIRECT ACTIVATION BY INTERNAL CALCIUM OF CHLORIDE CHANNELS IN ENDOTHELIAL-CELLS

The action of internal Ca2+ on Cl- channels in endothelial cells was s tudied by the whole-cell clamp technique in cultured human aortic endo thelial cells. Intracellular Ca2+ application by break-in of a Ca2+-co ntaining pipette solution produced an outward-rectifying Cl- current a fter a few minutes delay. The amplitude of the Cl- current increased w ith the increase in the internal Ca2+ concentration, producing a maxim al Cl- conductance as large as 2 nS/pF at pCa 5. The increase of the C a2+-induced Cl- conductance was also dependent on the internal ATP con centration. At pCa 5, the Cl conductance per cell was 61 nS at 5 mM AT P and 24 nS at 1 mM. The calmodulin antagonists trifluoperazine and W- 7 blocked the Cl- channel reversibly. The results suggest that Ca2+ ac tivates the Cl- channels indirectly via a calmodulin-mediated pathway, and that binding of ATP to the channel is a prerequisite for activati on.