IDENTIFICATION OF G-PROTEIN SUBTYPES IN PERIPHERAL-NERVE AND CULTURED SCHWANN-CELLS

In this study, we investigated the expression of various G proteins in whole sciatic nerves, in myelin and nonmyelin fractions from these nerves, and in membranes of immortalized Schwann cells. In myelin, nonmyelin, and Schwann cell membranes we detected two 39-40-kDa pertussis toxin substrates that were resolved on separation on urea-gradient gels. Two cholera toxin substrates with apparent molecular masses of 42 and 47 kDa were present in nerve and brain myelin and in Schwann cell membranes. In these membranes, a third 45-kDa cholera toxin substrate, which displayed the highest labeling, was also present. Immunoblotting with specific antisera allowed the identification of G(o)alpha, G(i1)alpha, G(i2)alpha, G(i3)alpha, G(q)/G11alpa, and the two isoforms of G(s)alpha in nerve homogenates, nerve, and brain myelin fractions. In Schwann cell membranes we identified G(o)alpha, G(i2)alpha, G(i3)alpha, and proteins from the G(q) family, but no immunoreactivity toward anti-G(il)alpha antiserum was detected. In these membranes, anti-G(s)alpha antibody recognized the three cholera toxin substrates mentioned above, with the 45-kDa band displaying the highest immunoreactivity. Relative to sciatic nerve myelin, the Schwann cell membranes revealed a significantly higher expression of G(i3)alpha and the absence of G(il)alpha. The different distribution of G proteins among the different nerve compartments might reflect the very specialized function of Schwann cells and myelin within the nerve.