DUAL ROLE OF CGMP IN MODULATION OF MACROMOLECULE PERMEABILITY OF AORTIC ENDOTHELIAL-CELLS

The effect of guanosine 3',5'-cyclic monophosphate (cGMP) on cytosolic Ca2+ dynamics and associated alterations in macromolecule permeabilit y was investigated in cultured monolayers of aortic endothelial cells. Addition of the membrane-permeable cGMP analogue 8-bromoguanosine 3', 5'-cyclic monophosphate (8-BrcGMP, 5 x 10(-4) M) or activators of the soluble (3-morpholinosydnonimine, 10(-5) M) or the particulate guanyly l cyclase (atrial natriuretic peptide, 10(-7) M) to unstimulated monol ayers led to a decrease in permeability (8-BrcGMP: 62 +/- 8% of contro l) without affecting low basal cytosolic Ca2+ concentration ([Ca2+](i) , 87 +/- 8 nM). In contrast, under conditions of elevated [Ca2+](i) (5 03 +/- 95 nM) and increased permeability (155 +/- 7% of control) induc ed by 10(-6) M ionomycin, 8-BrcGMP, 3-morpholinosydnonimine, or atrial natriuretic peptide provoked a further increase in permeability (8-Br cGMP: 255 +/- 27%). These agents failed to increase permeability when added before or after the ionomycin-triggered transitory rise in [Ca2](i). The increase in permeability in response to 8-BrcGMP was due to a secondary further rise in [Ca2+](i) (758 +/- 87 nM), which was aboli shed in the absence of extracellular Ca2+, indicating influx of exogen ous Ca2+ as the cause. Changes in [Ca2+](i) and permeability were inhi bited in the presence of the Rp diastereomer of 8-(4-chlorophenylthio) guanosine 3',5'-cyclic monophosphothioate (2 x 10(-5) M), an inhibitor of the cGMP-dependent protein kinase. These findings show that, depen ding on [Ca2+](i), cGMP can play opposite roles in endothelial permeab ility in one and the same cell preparation.