Differential localization and development-dependent expression of G-protein subunits, Go alpha and G beta, in rabbit...

Among various G-protein subunits identified in atrial and ventricular membranes from newborn and adult rabbits, the most remarkable developmental and tissue-specific differences were observed in the amounts of the alpha-subunit of Go (Go alpha) and the beta-subunit (G beta). Go alpha was abundant in atrial membranes especially from newborn rabbits but was barely detectable in ventricles. In contrast, G beta was present in both atrial and ventricular membranes. In both tissues the level of G beta-2 was much higher than that of G beta-1. Starting just after birth, the high levels of Go alpha in atria at term decreased gradually to about half of the amount in term animals, at 30 days of age, while the amount of G beta remained relatively constant until 26 days after birth. The levels of G beta in ventricles slowly declined during neonatal development. Similar developmental patterns were also observed when these parameters were studied in membranes isolated from cultured myocytes. Northern blot analysis showed the presence of mRNA for Go alpha-1A isoform in RNA samples from atria but not those from ventricles. The developmental expression of Go alpha-1A mRNA was somewhat different from that of Go alpha protein, whereas the time course of G beta mRNA expression was similar to that of G beta protein. Among other G-protein subunits tested, the amount of the splice variant of Gs protein, Gs alpha-1, in atrial as well as ventricular membranes increased with age of animals, while the amounts of Gs alpha-2, Gi alpha 2 and G alpha q/11 did not change significantly during development. These results indicate differential localization and tissue-specific developmental expression of G-protein subunits in rabbit heart.