EXPRESSION OF BETA-3-ADRENOCEPTORS IN RAT DETRUSOR SMOOTH-MUSCLE

Purpose: To investigate the expression of P-adrenoceptor (AR) subtypes responsible for detrusor smooth muscle relaxation. Materials and Meth ods: Isolated rat detrusor smooth muscle was examined by tension measu rement and reverse transcription polymerase chain reaction (RT-PCR).Re sults: Norepinephrine (NE), epinephrine (EP) and isoproterenol (ISO) w ere found to relax the detrusor muscle pre-contracted by 6 x 10(-7) M carbachol in the presence of 10(-6) M phentolamine. NE relaxed the det rusor muscle as potently as EP. This potency order (NE<is approximatel y equal to>EP) thus indicated the beta-ARs of the rat detrusor muscle to possibly be a beta 1 subtype. However, in the presence of 10(-6) M propranolol, beta 1- and beta 2- but not beta 3-AR antagonist, NE show ed a more potent relaxation than EP. This observation indicated that t he rat detrusor muscle also possesses beta 3-AR. RT-PCR revealed all t hree subtypes of beta-AR mRNA, namely beta 1-, beta 2- and beta 3-AR m RNA, to be expressed in rat detrusor smooth muscle cells. Conclusion: We concluded that beta 3-ARs exist in rat detrusor smooth muscle based on both pharmacological and molecular biological studies. Based on th ese findings, beta-ARs of rat detrusor smooth muscle are considered to be mixed populations consisting of three subtypes which play an impor tant role in relaxing smooth muscle in response to catecholamines.