1988 Volume 36 Issue 10 Pages 4081-4087
Characteristics of cardiac β-adrenergic responses in Suncus murinus (suncus) were examined in comparison with those of the rat. In both species, isoproterenol produced positive inotropic and chronotropic responses in spontaneously beating right atria and positive inotropic response in electrically driven papillary muscles. However, the effects of β-adrenoceptor stimulation in suncus papillary muscles were considerably smaller than in the rat. Tyramine, an indirect sympathomimetic amine, did not affect the contraction of ventricular muscle in suncus. The affinity and density of specific [3H] dihydroalprenolol binding sites in suncus atrium were close to those in rat atrium. On the other hand, specific [3H] dihydroalprenolol binding sites in suncus ventricle were distinctly lower both in affinity and in density than those of rat ventricle. These results suggest that ventricular β-adrenergic responses in the suncus are markedly smaller than those in the rat, probably due to lower density and affinity of β-adrenoceptors.
