Calmodulin inhibits calcium influx current in vascular endothelium

Utilizing the whole-cell configuration of the patch-clamp technique the effect of calmodulin (CaM) on thapsigargin-induced Ca2+ current has been studied. Addition of several concentrations of CaM to the patch pipette induced concentration-dependent inhibition of thapsigargin-induced Ca2+ current in bovine aortic endothelial cells. The effect of CaM was Ca2+ dependent and was not observed when the intracellular Ca2+ was buffered to 1 nM with EGTA. CaM produced two major effects on the thapsigargin-induced Ca2+ current. First CaM slow down activation of the current by thapsigargin from a control value of 16 +/- 5 to 31 +/- 6 s with 1 microM CaM in the pipette solution. The second effect of CaM was to reduce the current amplitude in a concentration-dependent manner. The inhibition of Ca2+ current was observed at the peak of the current and at the sustained current level. The reduction of current at the sustained level was observed 15-20 s after onset of the thapsigargin response. The half inhibitory concentration determined from these experiments was 0.1 microM. These results indicate that CaM can modulate thapsigargin-induced Ca2+ current in this endothelium, suggesting a possible role for CaM in the regulation of store-operated Ca2+ influx.