ENDOTHELIN-1 STIMULATES PROSTAGLANDIN-E2 PRODUCTION IN AN EXTRACELLULAR CALCIUM-INDEPENDENT MANNER IN CULTURED RAT MESANGIAL CELLS

To study a possible role of endothelin-1 (ET-1) in the regulation of glomerular function, we examined the presence of receptors for, and the biological action of, ET-1 in cultured rat mesangial (M) cells. The first-subcultured M cells prepared from isolated glomeruli of Sprague-Dawley rats were used. ET-1 binding was assayed by using I-125-ET-1. Inositol 1,4,5-trisphosphate (IP3) was determined by IP3-specific binding assay. Intracellular calcium ((i)Ca2+) was measured in fura-2 loaded cells. Prostaglandin E2 (PGE2) was measured by radioimmunoassay. In M cells there existed two classes of binding sites specific for ET-1 (K(d) was 0.24 and 4.4 nmol/L, B(max) was 130 and 1070 fmol/mg, respectively). ET-1 (10(-7)mol/L) induced a rapid and transient increase in IP3, followed by transient and sustained increases in (i)Ca2+. Nicardipine (10(-6)mol/L) inhibited only the sustained increase in (i)Ca2+. ET-1 (10(-9) mol/L to 10(-7) mol/L) significantly stimulated PGE2 production with the concentration dependency. Nicardipine (10(-6) mol/L) and diltiazem (10(-6) mol/L) did not inhibit the PGE2 production. We concluded that M cells have specific ET-1 receptors linked to phosphoinositide turnover and PGE2 production, and PGE2 production by ET-1 may be through an extracellular calcium-independent mechanism. Our results suggest that ET-1 plays an important role in the regulation of glomerular functions by modulating PGE2 production in M cells.