Two-dimensional distribution of G(i2 alpha) in the plasma membrane: a critical evaluation by immunocytochemistry

Caveolae have been postulated as a center for signal transduction, because many signaling molecules are concentrated in caveolin-rich fractions. We took G(i2 alpha) as an example and examined whether it is constitutively concentrated in caveolae. First, the behavior of caveolin and G(i2 alpha) in density-equilibrium ultracentrifugation was reexamined. By collecting fractions efficiently, caveolin and G(i2 alpha) were found to distribute differently. Secondly, by novel immunocytochemical methods it was found that the labeling density of G(i2 alpha) was 2.29 times higher in caveolae than in the non-caveolar plasma membrane. The results indicate that the concentration of G(i2 alpha) in caveolae is lower than deduced from most biochemical studies. (C) 1997 Federation of European Biochemical Societies.