engleski

A Direct Effect of Big Endothelin-1 in Rat Renal Proximal Tubule Cells

mediated through three subtypes of G-protein-coupled receptors, termed ETA, ETB and ETC. ET-1 activates ETA, and ETB receptors, respectively. Big ET-1 is a precursor of ET-1 and is generally considered as biologically inactive. However, there is some data indicating that big ET-1 might have direct effect on renal proximal tubules. To further investigate this possibility we used freshly isolated rat renal proximal tubules, where the ET receptors were downregulated by incubating proximal tubule cells with ET-1 (10^6M) for 45 min. Activity of ET receptors was assessed by measuring the increase in 1,2 diacylglycerol (DAG) in response to subsequent treatment with ET-1 or big ET-1. ET-1 did not evoke an increase in DAG (175,34,5 nmol/mg prot. vs. 159,035,1 nmol/mg prot.; con. vs. ET-1, N.S.), showing a successful downregulation of ET receptors. In contrast, incubation of proximal tubules with big ET-1 resulted in an increase in DAG in a dose- (344,88,8 nmol/mg prot., vs. 175,34,5 nmol/mg prot.; big ET-1 10^6M vs. con.,p0,01) and time-dependent manner (332,58,1 nmol/mg prot. vs. 209,77,0 nmol/mg prot., big ET-1 for 15 min. vs. con.,p0,05). The present results demonstrate a direct effect of big ET-1 in rat renal proximal tubule cells. Also, as the ETA and ETB receptors were downregulated, this effect of big-ET-1 may be mediated through a new subtype of endothelin receptors.

big endothelin-1; kidney; proximal tubule cells

nije evidentirano