EXPRESSION OF beta 3-ADRENOCEPTORS IN RAT DETRUSOR SMOOTH MUSCLE

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Abstract
To investigate the expression of beta-adrenoceptor (AR) subtypes responsible for detrusor smooth muscle relaxation. Isolated rat detrusor smooth muscle was examined by tension measurement and reverse transcription polymerase chain reaction (RT-PCR). Norepinephrine (NE), epinephrine (EP) and isoproterenol (ISO) were found to relax the detrusor muscle pre-contracted by 6 × 10−7 M carbachol in the presence of 10−6 M phentolamine. NE relaxed the detrusor muscle as potently as EP. This potency order (NE [equals, falling dots] 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 showed a more potent relaxation than EP. This observation indicated that the rat detrusor muscle also possesses beta 3-AR. RT-PCR revealed all three subtypes of beta-AR mRNA, namely beta 1-, beta 2- and beta 3-AR mRNA, to be expressed in rat detrusor smooth muscle cells. We concluded that beta 3-ARs exist in rat detrusor smooth muscle based on both pharmacological and molecular biological studies. Based on these findings, beta-ARs of rat detrusor smooth muscle are considered to be mixed populations consisting of three subtypes which play an important role in relaxing smooth muscle in response to catecholamines.