Developmental changes in adenylyl cyclase and GTP binding proteins in brown fat

Abstract

During the perinatal period, norepinephrine (NE)-stimulated adenylyl cyclase activity increased in interscapular brown adipose tissue (IBAT) membranes and then declined to adult levels by 23 days postpartum. The developmental patterns of NE- and NaF-stimulated activities were identical, indicating that the developmental increase in transmitter-stimulated activity resulted from the increased interaction of alpha-subunit of guanine nucleotide-binding stimulatory protein of adenylyl cyclase (Gs alpha) with the catalytic subunit (C). This increased Gs alpha-C interaction was the result of an increase in Gs alpha specific activity, as assessed in cyc- reconstitution assays, as well as an increased C activity, as assessed by forskolin-Mn(2+)-stimulated adenylyl cyclase activity. Although adenylyl cyclase activity increased during the perinatal period, total Gs alpha levels significantly declined because of the loss of the small-molecular-mass form of Gs alpha. Thus the ratio of large to small form of Gs alpha increased threefold and might have contributed to the perinatal increase in activity. Gi alpha-like proteins, as assessed by pertussis toxin-catalyzed [32P]ADP ribosylation, declined dramatically after birth. However, this loss of Gi alpha did not contribute to developmental changes in adenylyl cyclase activity because pertussis toxin treatment failed to alter NE-stimulated activity. In contrast to G alpha subunits, there were no changes in membrane levels of G beta subunits.