Levels of G-protein αq/11 subunits and of phospholipase C-β(1–4), -γ, and -δ1 isoforms in postmortem human brain caudate and cortical membranes: Potential functional implications

The levels of expression of G-protein αq/11 (Gαq/11) subunits and PLC-β(1–4), -γ, and -δ1 isoforms were quantified by Western blot analysis in order to establish their contribution to the patterns of PLC functioning reported here. Quantitative measurements of the levels of Gαq/11 subunits in each region were obtained by comparison with known amounts of Escherichia coli expressed recombinant Gαq subunits. Quantitative analysis indicated that Gαq/11 subunits are abundant polypeptides in human brain, with values ranging from about 1200 ng/mg in cerebral cortex to close to 900 ng/mg of membrane protein in caudate. In cerebral cortical membranes, the PLC-β1 isoform was more abundant than in caudate membranes. The highest levels of PLC-β2 expression were detected in caudate membranes. PLC-β3 was little expressed, and there were no significant differences in the relative values between both brain regions. Finally, the levels of the PLC-β4 isoform were significantly lower in caudate than in cortical membranes. It is concluded that although most of these data represent relative, not absolute, measures of protein levels within these regions, they contribute nonetheless to the significant differences observed in signaling capacities through the PLC system in both human brain regions.