REGULATED EXPRESSION OF ENDOTHELIN-1 IN GLOMERULAR CAPILLARY ENDOTHELIAL-CELLS

Endothelin (ET)-1 is a powerful vasoconstrictor known to be produced and secreted by endothelial cells lining large vessels. Because ET-1 stimulates glomerular mesangial cell contraction, glomerular capillary endothelial cells (GEN), normally situated in close apposition to mesangial cells, were examined for potential ET expression and secretion. Cultured bovine GEN released ET in a time-dependent fashion. ET secretion was significantly stimulated by bradykinin, an agonist known to activate phospholipase C in these cells. Preproendothelin 1 (preproET-1) mRNA levels in GEN rose in a biphasic manner on stimulation with bradykinin. The early increments (at 30 min) were not dependent on new protein synthesis, whereas the late rise (6 h after addition of bradykinin) appeared to be protein synthesis dependent. Neither early or late bradykinin-stimulated preproET-1 mRNA expression in glomerular endothelial cells was due to inhibition of mRNA breakdown. Both phases of preproET-1 mRNA expression were observed with other glomerular endothelial cell calcium-mobilizing agonists, namely thrombin, and were mimicked by the calcium ionophore ionomycin. By contrast, the protein kinase C activator phorbol myristate acetate only enhanced preproET-1 mRNA expression at 30 min and suppressed expression thereafter. It is concluded that GEN have the potential to express and secrete ET-1 in a phospholipase C-regulated fashion. Furthermore, because glomerular mesangial cells respond to this peptide, the findings raise the possibility of paracrine regulation of mesangial cell tone by glomerular endothelial cell-derived ET-1.