Endothelin Action and Production in Renal Tubular Cells

Abstract

Recent studies suggest that the renal tubule is not only a target of endothelin-1 (ET-1) but is also a possible source of endothelin. Thus, we attempted to detect specific preproET-1 messenger RNA (mRNA) as well as immunoreactive ET-1 secretion in renal epithelial cell lines. Madin-Darby canine kidney (MDCK) cells expressed a single 2.3 kb preproET-1 mRNA. In medium conditioned by MDCK for 24 hours there was a significant amount of immunoreactive ET-1 detected by sandwich type immunoassay. Both mRNA expression and mature ET-1 secretion were stimulated by an addition of transforming growth factor (TGF)-β to the basolateral side in a time-dependent manner, but the increase in peptide secretion lagged behind ET-1 mRNA expression by several hours. The basal secretion of ET-1 was polarized, with 2.3-fold greater secretion into the basolateral side over the apical side, while the difference was augmented to 7.5-fold by TGF-β. In contrast, LLCPK1 (pig kidney) cells secreted little ET-1 associated with a lower level of ET-1 mRNA expression. Regarding the effect of ET-1, it elicited [Ca2+]i transients in LLC-PK1 but not in MDCK. These data clearly show that renal tubules can express preproET-1 mRNA, synthesize mature ET-1, and secrete it preferentially to the basolateral side of the tubule cells, all of which are enhanced by TGF-β. The data suggest that ET- l produced by the renal tubule may function as a paracrine hormone in regulating tubular functions.