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We concluded that beta3-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.

1 By use of the reverse transcription polymerase chain reaction (RT-PCR), we determined the expression of adrenomedullin (AM) mRNA in the various tissues of the pig. To evaluate the signi®cance of the expression of AM mRNA, we also determined the eects of AM on the cytosolic Ca 2+ concentration ([Ca 2+ ] i ) and tension development of the porcine smooth muscle strips obtained from the coronary artery, pulmonary vein, trachea, ileum and urinary bladder. 2 AM mRNA was widely expressed in the porcine tissues examined, which included myocardium (left and right ventricle and right atrium), kidney, lung, endothelial cells (aorta and aortic valve), smooth muscles (aorta, main pulmonary artery, pulmonary vein, renal artery and vein, coronary artery, ileum, trachea and urinary bladder) and epithelial cells (trachea and urinary bladder). 3 AM induced a decrease in [Ca 2+ ] i and tension of the coronary artery, but not the pulmonary vein. AM had no eects on either the [Ca 2+ ] i or tension of the trachea and urinary bladder strips or on the tension development of strips of ileum. 4 These results indicated that AM has a role as an autocrine and/or paracrine regulator of the coronary arterial tone. AM probably does not have an important role in the regulation of the pulmonary venous, tracheal, ileac and urinary bladder smooth muscle tone, even though AM mRNA is expressed in these tissues; the functional signi®cance of AM in these smooth muscles remains to be determined.

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We concluded that beta3-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.

1 The mechanisms underlying the relaxation of the porcine renal artery induced by atrial natriuretic peptide (ANP) were investigated, using front-surface fluorimetry with fura-2 and receptor-coupled permeabilization by a-toxin.2 ANP decreased the cytosolic Ca2" concentration ([Ca2+] [Ca2+l]. 6 These results indicate that ANP induces relaxation of the porcine renal artery by: (1) reducing [Ca2+], mainly via the activation of the Ca2+ pumps located on the sarcoplasmic reticulum and sarcolemma, as well as via inhibition of agoinist-induced release of Ca2+ from the intracellular store; and (2) decreasing the Ca2+-sensitivity of the contractile elements.

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