A B S T R A C TThe aim of this study was to characterize endothelin receptor subtypes of the detrusor muscle of the human urinary bladder. The receptor subtypes mediating endothelin (ET)-1-induced activity in the human detrusor smooth muscles have been characterized using isometric contraction and reverse transcription-polymerase chain reaction (RT-PCR). ET-1 (a nonselective ET receptor agonist ; 10 − 10 M to 10 − 6 M) exhibited concentration-dependent contractions in human urinary bladder with a plateau at concentrations above 3i10 − 7 M. Neither IRL1620 nor sarafotoxin S6c (both ET B -selective agonists ; 10 − 10 M to 10 − 6 M) elicited contractile activity in the human urinary bladder detrusor smooth muscle. FR139317 (an ET A -selective antagonist ; 10 − 7 M to 10 − 5 M) produced a marked shift to the right of the ET-1 concentrationresponse curve in human urinary bladder detrusor smooth muscle (from the Schild plot TpA 2 l 7.96 ; slope l 0.95). In contrast, RES701-1 (an ET B -selective antagonist ; 10 − 7 M to 10 − 5 M) had no effect on the ET-1 concentration-response curve. RT-PCR revealed positive amplification of ET A receptor mRNA fragment, but not ET B . These results indicate that the ET-1-induced contractile effects of urinary bladder detrusor smooth muscle seem to be mediated mainly by the ET A receptor, not by the ET B receptor.
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