(1/103) Functional and molecular biological evidence for a possible beta3-adrenoceptor in the human detrusor muscle.

The possible existence of a beta3-adrenergic receptor (beta3-AR) in the human detrusor muscle was investigated by in vitro functional studies and analysis of mRNA expression. Isoprenaline, noradrenaline and adrenaline each produced a concentration-dependent relaxation of the human detrusor. The rank order for their relaxing potencies was isoprenaline (pD2 6.37+/-0.07) > or = noradrenaline (pD2 6.07+/-0.12) > or = adrenaline (pD2 5.88< or =0.11). Neither dobutamine (beta1- and beta2-AR agonist) nor procaterol (beta2-AR agonist) produced any significant relaxation at concentrations up to 10(-5) M. BRL37344A, CL316243 and CGP-12177A (beta3-AR agonists), relaxed the preparations significantly at concentrations higher than 10(-6) M. The pD2 values for BRL37344A, CL316243 and CGP-12177A were 6.42+/-0.25, 5.53+/-0.09 and 5.74+/-0.14, respectively. CGP-20712A (10(-7) - 10(-5) M), a beta1-AR antagonist, did not affect the isoprenaline-induced relaxation. On the other hand, ICI-118,551, a beta2-AR antagonist, produced a rightward parallel shift of the concentration-relaxation curve for isoprenaline only at the highest concentration used (10(-5) > M) and its pKB value was 5.71+/-0.19. Moreover, SR58894A (10(-7) - 10(-5) M), a beta3-AR antagonist, caused a rightward shift of the concentration-relaxation curve for isoprenaline in a concentration-dependent manner. The pA2 value and slope obtained from Schild plots were 6.24+/-0.20 and 0.68+/-0.31. The beta1-, beta2- and beta3-AR mRNAs were all positively expressed in detrusor smooth muscle preparations in a reverse transcription polymerase chain reaction assay. In conclusion, the present results provide the first evidence for the existence of the beta3-AR subtype in the human detrusor. They also suggest that the relaxation induced by adrenergic stimulation of the human detrusor is mediated mainly through beta3-AR activation.  (+info)

(2/103) Constitutively active mutants of the beta1-adrenergic receptor.

We provide the first evidence that point mutations can constitutively activate the beta(1)-adrenergic receptor (AR). Leucine 322 of the beta(1)-AR in the C-terminal portion of its third intracellular loop was replaced with seven amino acids (I, T, E, F, C, A and K) differing in their physico-chemical properties. The beta(1)-AR mutants expressed in HEK-293 cells displayed various levels of constitutive activity which could be partially inhibited by some beta-blockers. The results of this study might have interesting implications for future studies aiming at elucidating the activation process of the beta(1)-AR as well as the mechanism of action of beta-blockers.  (+info)

(3/103) Dobutamine as selective beta(1)-adrenoceptor agonist in in vivo studies on human thermogenesis and lipid utilization.

The use of dobutamine as selective beta(1)-adrenoceptor agonist in in vivo studies on human thermogenesis and lipid utilization was investigated in 20 men. At 2.5, 5, and 10 microg x kg(-1) x min(-1), dobutamine induced significant increases in energy expenditure, lipid oxidation, and lipolysis. The beta(1)-adrenoceptor antagonist atenolol (bolus: 42.5 microg/kg, infusion: 1.02 microg x kg(-1) x min(-1)) blocked all dobutamine-induced effects on thermogenesis and lipid utilization. All parameters remained at levels comparable to those during saline infusion. The dose of atenolol used did not inhibit beta(2)-adrenoceptor-specific changes in energy expenditure, lipid oxidation, and lipolysis during salbutamol infusion (85 ng x kg(-1) x min(-1)). This indicates that atenolol was specific for beta(1)-adrenoceptors and did not camouflage concomitant beta(2)-adrenoceptor stimulation during dobutamine infusion. Therefore, we conclude that dobutamine can be used as a selective beta(1)-adrenoceptor agonist at dosages +info)

(4/103) Binding pockets of the beta(1)- and beta(2)-adrenergic receptors for subtype-selective agonists.

We examined the subtype-selective binding site of the beta-adrenergic receptors (betaARs). The beta(1)/beta(2)-chimeric receptors showed the importance of the second and seventh transmembrane domains (TM2 and TM7) of the beta(2)AR for the binding of the beta(2)-selective agonists such as formoterol and procaterol. Alanine-substituted mutants of TM7 of the beta(2)AR showed that Tyr(308,) located at the top of TM7, mainly contributed to beta(2) selectivity. However, Tyr(308) interacted with formoterol and procaterol in two different ways. The results of Ala- and Phe-substituted mutants indicated that the phenyl group of Tyr(308) interacted with the phenyl group in the N-substituent of formoterol (hydrophobic interaction), and the hydroxyl group of Tyr(308) interacted with the protonated amine of procaterol (hydrophilic interaction). In contrast to beta(2)AR, TM2 is a major determinant that beta(1)-selective agonists such as denopamine and T-0509 bound the beta(1)AR with high affinity. Three amino acids (Leu(110), Thr(117), and Val(120)) in TM2 of the beta(1)AR were identified as major determinants for beta(1)-selective binding of these agonists. Three-dimensional models built on the basis of the predicted structure of rhodopsin showed that Tyr(308) of the beta(2)AR covered the binding pocket formed by TM2 and TM7 from the upper side, and Thr(117) of the beta(1)AR located in the middle of the binding pocket to provide a hydrogen bonding for the beta(1)-selective agonists. These data indicate that TM2 and TM7 of the betaAR formed the binding pocket that binds the betaAR subtype-selective agonists with high affinity.  (+info)

(5/103) Identification of the endophilins (SH3p4/p8/p13) as novel binding partners for the beta1-adrenergic receptor.

Several G-protein coupled receptors, such as the beta1-adrenergic receptor (beta1-AR), contain polyproline motifs within their intracellular domains. Such motifs in other proteins are known to mediate protein-protein interactions such as with Src homology (SH)3 domains. Accordingly, we used the proline-rich third intracellular loop of the beta1-AR either as a glutathione S-transferase fusion protein in biochemical "pull-down" assays or as bait in the yeast two-hybrid system to search for interacting proteins. Both approaches identified SH3p4/p8/p13 (also referred to as endophilin 1/2/3), a SH3 domain-containing protein family, as binding partners for the beta1-AR. In vitro and in human embryonic kidney (HEK) 293 cells, SH3p4 specifically binds to the third intracellular loop of the beta1-AR but not to that of the beta2-AR. Moreover, this interaction is mediated by the C-terminal SH3 domain of SH3p4. Functionally, overexpression of SH3p4 promotes agonist-induced internalization and modestly decreases the Gs coupling efficacy of beta1-ARs in HEK293 cells while having no effect on beta2-ARs. Thus, our studies demonstrate a role of the SH3p4/p8/p13 protein family in beta1-AR signaling and suggest that interaction between proline-rich motifs and SH3-containing proteins may represent a previously underappreciated aspect of G-protein coupled receptor signaling.  (+info)

(6/103) Analysis of domain responsible for desensitization of beta1-adrenergic receptor.

When the wild type beta1-adrenergic receptor (WT-beta1AR) was expressed in Sf9 cells, the beta1AR-stimulated adenylyl cyclase activities were desensitized by prior treatment with isoproterenol. The extent of beta1AR desensitization was not modified, and the onset was not promoted by the overexpression of G protein-coupled receptor kinase 2 (GRK2), GRK5 or GRK6. However, overexpression of the dominant negative mutant of GRK2 appeared to inhibit desensitization of the beta1AR. The change of the potential protein kinase A phosphorylation site located at the intracellular third loop did not affect beta1AR desensitization. Desensitization of the truncated mutant, in which nearly all of the serine and threonine residues from the carboxyl terminus were eliminated, was the same as that of the WT-beta1AR. A deletion mutant that lacked serine and threonine residues of the intracellular third loop was also desensitized by isoproterenol stimulation. Furthermore, the deletion of serine and threonine residues from both the intracellular third loop and carboxyl terminus did not affect desensitization of the beta1AR. These results suggested that phosphorylation by endogenous GRKs in Sf9 cells contributed to desensitization of the beta1AR and that the regions other than third intracellular loop and carboxyl terminus may be responsible for beta1AR desensitization.  (+info)

(7/103) Regulation of beta 1- and beta 3-adrenergic agonist-stimulated lipolytic response in hyperthyroid and hypothyroid rat white adipocytes.

1. This study examined the effects of thyroid status on the lipolytic responses of rat white adipocytes to beta-adrenoceptor (beta-AR) stimulation. The beta 1- and beta 3-AR mRNAs and proteins were measured by Northern and saturation analyses, respectively. Glycerol production and adenyl cyclase (AC) activity induced by various non-selective and selective beta 1/beta 3-AR agonists and drugs which act distal to the receptor in the signalling cascade were measured in cells from untreated, triiodothyronine (T3)-treated and thyroidectomized rats. 2. The beta 3-AR density was enhanced (72%) by T3-treatment and reduced (50%) by introduction of a hypothyroid state while beta 1-AR number remained unaffected. The beta 1- and beta 3-AR density was correlated with the specific mRNA level in all thyroid status. 3. The lipolytic responses to isoprenaline, noradrenaline (beta 1/beta 3/beta 3-AR agonists) and BRL 37344 (beta 3-AR agonist) were potentiated by 48, 58 and 48%, respectively in hyperthyroidism and reduced by about 80% in hypothyroidism. 4. T3-treatment increased the maximal lipolytic response to the partial beta 3-AR (CGP 12177) and beta 1-AR (xamoterol) agonists by 234 and 260%, respectively, increasing their efficacy (intrinsic activity: 0.95 versus 0.43 and 1.02 versus 0.42). The maximal AC response to these agonists was increased by 84 and 58%, respectively, without changing their efficacy. 5. In the hypothyroid state, the maximal lipolytic and AC responses were decreased with CGP (0.17 +/- 0.03 versus 0.41 +/- 0.08 mumol glycerol/10(6) adipocytes; 0.048 +/- 0.005 versus 0.114 +/- 0.006 pmol cyclic AMP min-1 mg-1) but not changed with xamoterol. 6. The changes in lipolytic responses to postreceptor-acting agents (forskolin, enprofylline and dibutenyl cyclic AMP, (Bu)2cAMP) suggest the modifications on receptor coupling and phosphodiesterase levels in both thyroid states. 7. Thyroid status affects lipolysis by modifying beta 3-AR density and postreceptor events without changes in the beta 1-AR functionality.  (+info)

(8/103) Differential adrenergic regulation of the gene expression of the beta-adrenoceptor subtypes beta1, beta2 and beta3 in brown adipocytes.

In brown adipocytes, fundamental cellular processes (cell proliferation, differentiation and apoptosis) are regulated by adrenergic stimulation, notably through beta-adrenergic receptors. The presence of all three beta-receptor subtypes has been demonstrated in brown adipose tissue. Due to the significance of the action of these receptors and indications that the subtypes govern different processes, the adrenergic regulation of the expression of the beta(1)-(,) beta(2)- and beta(3)-adrenoceptor genes was examined in murine brown-fat primary cell cultures. Moderate levels of beta(1)-receptor mRNA, absence of beta(2)-receptor mRNA and high levels of beta(3)-receptor mRNA were observed in mature brown adipocytes (day 6 in culture). Noradrenaline (norepinephrine) addition led to diametrically opposite effects on beta(1)- (markedly enhanced expression) and beta(3)-gene expression (full cessation of expression, as previously shown). beta(2)-Gene expression was induced by noradrenaline, but only transiently (<1 h). The apparent affinities (EC(50)) of noradrenaline were clearly different (7 nM for the beta(1)-gene and+info)

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