β3-AR and the vertebrate heart: a comparative view

Recent cardiovascular research showed that, together with (1)- and (2)-adrenergic receptors (ARs), (3)-ARs contribute to the catecholamine (CA)-dependent control of the heart. (3)-ARs structure, function and ligands were investigated in mammals because of their applicative potential in human cardiovascular diseases. Only recently, the concept of a (3)-AR-dependent cardiac modulation was extended to non-mammalian vertebrates, although information is still scarce and fragmentary. (3)-ARs were structurally described in fish, showing a closer relationship to mammalian (1)-AR than (2)-AR. Functional (3)-ARs are present in the cardiac tissue of teleosts and amphibians. As in mammals, activation of these receptors elicits a negative modulation of the inotropic performance through the involvement of the endothelium endocardium (EE), G(i/0) proteins and the nitric oxide (NO) signalling. This review aims to comparatively analyse data from literature on (3)-ARs in mammals, with those on teleosts and amphibians. The purpose is to highlight aspects of uniformity and diversity of (3)-ARs structure, ligands activity, function and signalling cascades throughout vertebrates. This may provide new perspectives aimed to clarify the biological relevance of (3)-ARs in the context of the nervous and humoral control of the heart and its functional plasticity.