Differentiation of cultured brown adipocytes is associated with a selective increase in the short variant of G sα protein. Evidence for higher functional activity of G sαS

Abstract

In order to examine whether the differentiation process in brown adipocytes cultivated in primary culture is associated with substantial alterations in the complement of G proteins, the levels of these proteins were investigated with immuno-electrophoretic techniques in membrane preparations from proliferating and differentiated cultured mouse brown adipocytes. We observed that differentiation was associated with a dramatic (more than threefold) increase in the short variant of G sα protein (G sαS). The long variant of G sα (G sαL), as well as G i1α, G i2α, G qα, G 11α and Gβ subunit proteins remained unchanged whereas G i3α protein was decreased. These changes were accompanied by marked increase in isoprenaline-, forskolin- as well as manganese-stimulated adenylyl cyclase. Thus, the marked increase in β-adrenergic responsiveness of fully differentiated confluent brown adipocytes (day 8–9), as compared with that of proliferating undifferentiated cells of ‘fibroblast phenotype’ (day 3–4), is associated with a significant increase in the relative proportion between the short and long variants of G sα (the G sαS/G sαL ratio) along with a decrease in G i3α protein. These data also suggest that the short variant of G sα exhibits higher functional activity than the long variant of this G protein.