beta3-adrenoceptor modulates cardiac function of the frog Rana esculenta

3-adrenergic receptors (ARs) have been recently identified in mammalian hearts where, unlike 1- and 2-ARs, induce cardiosuppressive effects. The aim of this study was to describe 3-AR role in the frog (Rana esculenta) heart and to examine its signal transduction pathway. The presence of 3-AR, by using Western blotting analysis, has been also identified. BRL37344, a selective 3-AR agonist, induced a dose-dependent negative inotropic effect at concentrations from 10-12 to 10-6 M. This effect was not modified by nadolol, a 1/2-AR antagonist, and by phentolamine (-AR antagonist), but it was suppressed by the 3-AR-specific antagonist SR59230 and by exposure to a the Gi/o proteins inhibitor Pertussis Toxin. In addition, the involvement of EE-NOS-cGMP-PKG/PDE2 pathway in the negative inotropism of BRL37344 has been assessed. BRL37344 treatment induced eNOS and AkT phosphorylation as well as an increase of cGMP levels. 3-ARs activation induced a non competitive antagonism against ISO stimulation which disappeared in presence of PKG and PDE2 inhibition. Taken together our findings provide, for the first time the evidence of the 3-ARs presence in the frog heart, highlighting a role in the cardiac performance modulation which involves Gi/o protein and occurs via an EE-NO-cGMP-PKG/PDE2 cascade