1. Left atrial strips from transgenic (TG4) @entity19 with cardiac-specific overexpression ( approximately 200-fold) of the @entity21167 ( @entity21167 ) were isolated, and their isometric force of contraction (F(c)) in response to electrical stimulation was measured. 2. The betaAR agonist @entity3044 elicited negative inotropic responses in all left atrial strips; in 6/11 preparations, it also had a small positive inotropic effect. This 'up-phase' was observed from 0.1 to 10 nM, with the 'down-phase' occurring at higher concentrations. Both phases were mediated by @entity21167 , as shown by their sensitivity to the @entity21167 antagonist @entity10342 (100 nM; pA(2) 8.60+/-0.07, 8.45+/-0.19, for 'up-phase' and 'down-phase,' respectively), but not the @entity11951 antagonist @entity14528 (100 nM). Conversely, nontransgenic littermate preparations responded to @entity3044 treatment solely by an increase in F(c), which was @entity11951 -mediated. 3. Pretreatment of left atrial strips with either 10 nM @entity3044 or 1 mM @entity5987 significantly attenuated the TG4 'up-phase', while having no effect on either the TG4 'down-phase' or the littermate controls' responses. @entity7320 toxin treatment of the animals prevented @entity3044 's negative inotropic effects in TG4 preparations, but had no effect in littermate controls. 4. The findings imply that the responses of TG4 left atrium to @entity3044 are because of @entity21167 coupling to G(s) and G(i) proteins, consistent with the model of Daaka et al., in which protein kinase A phosphorylation of the @entity21167 causes a switch from G(s) to G(i) protein coupling.

Cardiac-specific overexpression of human beta2 adrenoceptors in XXXX exposes coupling to both Gs and Gi proteins.

@entity7320 :: ('520', 'Species') :: ['B. pertussis'] @entity10342 :: ('MESH:C026777', 'Chemical') :: ['ICI-118,551'] @entity19 :: ('10090', 'Species') :: ['mice'] @entity21167 :: ('11555(Tax:10090)', 'Gene') :: ['beta(2) adrenoceptor', 'beta(2)AR'] @entity11951 :: ('11554(Tax:10090)', 'Gene') :: ['beta(1)AR'] @entity14528 :: ('MESH:C049763', 'Chemical') :: ['CGP-20712A'] @entity5987 :: ('MESH:D015124', 'Chemical') :: ['8-bromo-cAMP'] @entity3044 :: ('MESH:D007545', 'Chemical') :: ['isoprenaline']
@entity19 :: (10090,Species) :: ['mice']
