Two‐dimensional distribution of Gi2α in the plasma membrane: a critical evaluation by immunocytochemistry

Abstract
Caveolae have been postulated as a center for signal transduction, because many signaling molecules are concentrated in caveolin-rich fractions. We took Gi2α as an example and examined whether it is constitutively concentrated in caveolae. First, the behavior of caveolin and Gi2α in density-equilibrium ultracentrifugation was reexamined. By collecting fractions efficiently, caveolin and Gi2α were found to distribute differently. Secondly, by novel immunocytochemical methods it was found that the labeling density of Gi2α was 2.29 times higher in caveolae than in the non-caveolar plasma membrane. The results indicate that the concentration of Gi2α in caveolae is lower than deduced from most biochemical studies.