Differential Localization and Development-dependent Expression of G-protein Subunits, Goα and Gβ, in Rabbit Heart

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 α-subunit of Go (Goα) and the β-subunit (Gβ). Goα was abundant in atrial membranes especially from newborn rabbits but was barely detectable in ventricles. In contrast, Gβ was present in both atrial and ventricular membranes. In both tissues the level of Gβ-2 was much higher than that of Gβ-1. Starting just after birth, the high levels of Goα in atria at term decreased gradually to about half of the amount in term animals, at 30 days of age, while the amount of Gβ remained relatively constant until 26 days after birth. The levels of Gβ 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 Goα-1A isoform in RNA samples from atria but not those from ventricles. The developmental expression of Goα-1A mRNA was somewhat different from that of Goα protein, whereas the time course of Gβ mRNA expression was similar to that of Gβ protein. Among other G-protein subunits tested, the amount of the splice variant of Gs protein, Gsα-1, in atrial as well as ventricular membranes increased with age of animals, while the amounts of Gsα-2, Giα2 and Gαq/11 did not change significantly during development. These results indicate differential localization and tissue-specific developmental expression of G-protein subunits in rabbit heart.