Identification of GTP binding proteins in brain microvessels and their role in phosphoinositide turnover

The identity of GTP binding proteins in cerebral microvessels was investigated by immunoblotting. Data indicate the presence of a characteristic pattern of Gi, Gs and Go. The most remarkable finding is the presence of Go protein in cerebral microvessels that consist predominantly of capillary segments free of neuronal contaminants. The pattern of pertussis toxin-catalyzed ADP-ribosylation of a 40 kDa polypeptide is characteristic of the Gi/Go type alpha-subunits. In addition, we have observed that GTP tau S, a non-hydrolyzable guanine nucleotide, exerts a dual regulatory effect on phosphoinositide metabolism depending on the concentration, thus 10(-7) M concentration inhibits the 32P incorporation into PIP2 and PA by a pertussis toxin-sensitive mechanism; on the contrary, the stimulatory effect of higher concentration than 10(-6) M of GTP tau S is pertussis toxin-insensitive.