EFFECT OF AGE ON BETA-RECEPTORS, G(S-ALPHA)-PROTEIN AND G(I-ALPHA)-PROTEIN IN RAT-HEART

beta-adrenoceptors, G(s alpha)- and G(i alpha)- proteins were investig ated in a crude plasma membrane preparation from ventricles of young ( 2-4 months) and senescent (22-24 months) Wistar rats. Receptor density , ligand affinity and beta(1)/beta(2)-receptor ratio were independent of the age of the rats. The percentage of beta-receptors coupled to G- proteins increased with age. An age-related increase in the level of G (s alpha) (124%) was paralleled by an increase in the ratio between th e high and low molecular weight form of G(s alpha). The level of G(i a lpha)-protein almost doubled (170%) upon aging. We conclude that the a ge-related differences are small at the level of the beta-adrenoceptor molecule, but that the increase in G(i alpha)-proteins could be respo nsible for the age-related reduction in myocardial inotropic and chron otropic responses. Moreover, we suggest that the changes in degree of high affinity coupling between beta-receptor and G(s)- protein are pos sibly linked to alterations in the ratio between the G(s)-molecular we ight subtypes.