INHIBITION OF AGONIST-INDUCED CA2-CELLS BY MYOSIN LIGHT-CHAIN KINASE INHIBITOR( ENTRY IN ENDOTHELIAL)

Identification of the signal which links the depletion of Ca2+ stores to a Ca2+ entry pathway in the plasma membrane remains to be determine d. In the present study, effects of ML-9 and wortmannin, inhibitors of myosin light-chain kinase (MLCK), on agonist-stimulated Ca2+ response were investigated in porcine aortic endothelial cells loaded with the Ca2+-sensitive dye fura-2. Bradykinin (BK) caused a rapid increase in [Ca2+](i), followed by a sustained increase due to the influx of Ca2 from the extracellular space. ML-9 almost completely abolished the su stained increase in [Ca2+](i) in BK-stimulated cells, while it did not affect the mobilization of Ca2+ from intracellular stores. ML-9 also abolished the sustained increase in [Ca2+](i) caused by thapsigargin. Wortmannin mimicked the effect of ML-9 on the thapsigargin-stimulated Ca2+ response. These findings document for the first time the involvem ent of MLCK inhibitor in Ca2+ signaling in endothelial cells. (C) 1996 Academic Press, Inc.