Endothelin-induced inositol phosphate formation in rat kidney. Studies on receptor subtypes, G-proteins and regulation during ontogenesis.

The aim of this study was to characterize the properties of endothelin (ET)-receptor subtypes mediating inositol phosphate (IP)-formation in rat kidney and their regulation during ontogenesis. In renal cortical slices of adult rats (12-16 weeks old) ET's concentration-dependently increased IP-formation with an order of potency ET-1 >> ET-3. While the non-selective ET-receptor antagonist bosentan (10 microM) completely suppressed ET-induced IP-formation, the ETA-receptor antagonist BQ-123 (10 microM) inhibited it only by 70%, the ETB-receptor antagonist IRL 1038 (1 microM) by 25%; combined application of BQ-123 + IRL 1038 caused complete inhibition of ET-1-induced IP-formation. Pretreatment of isolated renal cells with pertussis toxin (PTX, 500 ng/ml) overnight did not attenuate but significantly increased ET-1-induced IP-formation. Ontogenetic studies in renal sites from neonatal, 1, 2, 3, 6, 12 and 24 weeks old rats revealed that ET-1-induced IP-formation maturation-dependently declined being highest in neonatal rats (increase: 169% over basal) and lowest in 24 weeks old rats (increase: 47% over basal). This decline in ET-induced IP-formation was accompanied by a decrease in renal ET-receptor number and the amount of immunodetectable Gq/11 (assessed by Western-blotting using the QL-antiserum). Moreover, ET-receptor subtypes changed during the maturation process: from neonates to 12 weeks old rats number and functional responsiveness of ETA-receptors declined, while that of ETB-receptors increased. We conclude that in adult rat renal cortex ET-induced IP-formation is mediated by activation of both ETA- and ETB-receptors and does not involve a PTX-sensitive G-protein. ET-induced IP-formation declines during the maturation process; this is associated with a decrease in ET-receptor number and the immunodetectable amount of Gq/11.