Expression of guanine-nucleotide-binding proteins in lean and obese insulin-resistant mice

To examine whether G protein were affected in the obese insulin-resistant state, the level of various G proteins (alpha i1, alpha i2, alpha i3, alpha o and alpha s) was assessed by immunodetection in lean and experimentally induced obese mice. Crude membranes were prepared from adipose tissues, muscle, liver, kidney and brain. G alpha-subunits were similar in lean and obese animals in brain, kidney, skeletal or heart muscle. Hepatic G alpha s, G alpha i2 and G alpha i3 subunits were markedly elevated in obese mice. When total tissue contents were considered, interscapular brown adipose tissue and epididymal fat pads from obese animals contained more alpha i2 than the lean tissues, while alpha i1, alpha i3 and alpha s were similar in both groups. However, when expressed per mg of membrane protein, alpha i1, alpha i3 and alpha s were decreased and alpha i2 was normal in white adipose tissue of obese animals. Thus the expression of the G protein alpha-subunits seems to be regulated by tissue-specific factors rather than by circulating factors.