REGIONAL DISTRIBUTION AND QUANTITATIVE MEASUREMENT OF THE PHOSPHOINOSITIDASE C-LINKED GUANINE-NUCLEOTIDE-BINDING PROTEIN-G11-ALPHA AND PROTEIN-GQ-ALPHA IN RAT-BRAIN

Levels of the guanine nucleotide binding proteins G11alpha and G(q)alpha, which produce receptor regulation of phosphoinositidase C, were measured immunologically in 13 regions of rat central nervous system. This was achieved by immunoblotting membranes from these regions with antisera (CQ series) that identify these two polypeptides equally, following separation of the membranes using sodium dodecyl sulphate-polyacrylamide gel electrophoresis conditions that can resolve G(q)alpha and G11alpha. In all regions examined, G(q)alpha was more highly expressed than G11alpha. Ratios of levels of G(q)alpha to G11alpha varied between the regions from 5:1 to 2:1. Quantitative measurements of the levels of G(q)alpha and G11alpha in each region were obtained by comparison with known amounts of purified liver G(q)alpha and G11alpha and with E. coli expressed recombinant G(q)alpha. Areas that expressed G(q)alpha highly included olfactory bulb (930 ng/mg of membrane protein), frontal cortex (700 ng/mg of membrane protein), parietal occipital cortex (670 ng/mg of membrane protein), caudate putamen (1,003 ng/mg of membrane protein), hippocampus (1,045 ng/mg of membrane protein), hypothalamus (790 ng/mg of membrane protein), and cerebellum (950 ng/mg of membrane protein). More modest levels were observed in thalamus (450 ng/mg of membrane protein), pituitary (480 ng/mg of membrane protein), optic chiasma (330 ng/mg of membrane protein), and spinal cord (350 ng/mg of membrane protein). G11alpha was more evenly expressed with values ranging from about 170 ng/mg of membrane protein in spinal cord and optic chiasma to close to 300 ng/mg of membrane protein in regions expressing high levels of G(q)alpha. A third polypeptide could be identified by the CQ antisera in all brain regions. The possibility that this polypeptide is the alpha subunit of G14 is discussed.