LOCALIZATION AND POLAR DISTRIBUTION OF SEVERAL G-PROTEIN SUBUNITS ALONG NEPHRON SEGMENTS

Guanine nucleotide binding proteins (G-proteins) are heterotrimeric proteins involved in signal transduction in epithelia. In addition to possessing a polarized epithelium the nephron is composed of well defined segments, each with distinct receptors, transporters and other functions. Since different G-proteins interact with different receptors, a differential distribution of the various G-protein subunits would be expected. To investigate this possibility, polyclonal antipeptide antibodies to several G-protein subunits were used to examine the distribution of these proteins in nephron segments and their localization to apical or basal membrane domains. Immunoblotting of cortical membrane vesicles demonstrated the presence of G-proteins in both the brush border and basolateral membrane. Staining with G(alpha) common and G(alpha-s) antibodies demonstrated more of these G-protein subunits in the brush border than basolateral membrane. G-protein beta-subunits were also present in greater quantity in brush border membranes. Immunocytochemical analysis demonstrated good antigenic preservation and basically confirmed the results of immunoblotting of renal cortex. G-proteins were also found to be differentially distributed in the medulla, the amounts increasing with proximity to inner medulla. Only G(alpha-s) and G(beta) subunits were demonstrated in glomeruli, but ail subunits examined were detected in brush borders of proximal and apical membrane of distal tubules in cortex. In outer medulla G(alpha-s) was detected in both basolateral and brush borders of some tubules and only brush borders of others. G(alpha-i2) and G(beta) were found in brush border and G(alpha-i3) was not detected in this area. Basolateral membranes of inner medulla contained G(alpha-s) G(alpha-i3) and G(beta) subunits: G(alpha-i3) was also present in apical membranes in some tubules. G(alpha-i2) was detected only in apical membranes in this region. We conclude that G-proteins are differentially distributed in nephron segments. Investigation of regional tubular function may disclose a role for the G-proteins we have localized.