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 permeability 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 guanylyl cyclase (atrial natriuretic peptide, 10(-7) M) to unstimulated monolayers led to a decrease in permeability (8-BreGMP: 62 +/- 8% of control) without affecting low basal cytosolic Ca2+ concentration ([Ca2+]i, 87 +/- 8 nM). In contrast, under conditions of elevated [Ca2+]i (503 +/- 95 nM) and increased permeability (155 +/- 7% of control) induced by 10(-6) M ionomycin, 8-BrcGMP, 3-morpholinosydnonimine, or atrial natriuretic peptide provoked a further increase in permeability (8-BrcGMP: 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 abolished in the absence of extracellular Ca2+, indicating influx of exogenous Ca2+ as the cause. Changes in [Ca2+]i and permeability were inhibited, 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, depending on [Ca2+]i, cGMP can play opposite roles in endothelial permeability in one and the same cell preparation.