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.

M130 , also induced leftward shifts of the [Ca¥]é-force relationship (EC50 of Ca¥: 65 nÒ, 72 nÒ and 180 nÒ, respectively). However, these required no pre-incubation. 4. Deletion of residues 304-374 from the most potent construct, M130 1-374 , abolished the Ca¥sensitizing effect. 5. Wortmannin inhibited the enhancement of contraction induced by M130 fragments when added before contraction was initiated and partially inhibited the effects when added after steady-state contraction. 6. M1301-374 slowed the rate of relaxation in Ca¥-free medium. The time for 50% relaxation with this fragment was 510 ± 51 s, compared with 274 ± 14 s for control. 7. The levels of myosin light chain phosphorylation (22•4%) and force (34•5%) obtained with 300 nÒ Ca¥ were increased by 3 ìÒ M130 1-374 to 35•7 and 92•2%, respectively. However, M1301-374 had no effect on the phosphorylation-force relationship. 8. In conclusion, the NHµ-terminal M130 fragments containing residues 304-374 inhibited myosin phosphatase, increased myosin light chain phosphorylation and increased the Ca¥ sensitivity of the contractile apparatus in permeabilized porcine renal artery.

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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.

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