CHARACTERIZATION OF G-PROTEINS IN RAT MYOMETRIUM - A DIFFERENTIAL MODULATION OF GI2-ALPHA AND GI3-ALPHA DURING GESTATION

Myometrial membranes, obtained from estrogen-dominated (day 0) rat uteri, were immunoblotted with antiserum (SG1), which recognizes the alpha subunits of both G(i)1 and G(i)2, with antiserum (LE2) specific for G(i)2-alpha, and with I3B antiserum, specific for G(i)3-alpha. The data revealed the absence of detectable levels of G(i)1-alpha and the simultaneous presence of G(i)2-alpha and G(i)3-alpha as G(i) subunits in rat myometrium. The expression of G(i) proteins during gestation (days 0, 12, 21) was studied with the above antibodies. No qualitative change in the nature of G(i)-alpha species was observed during gestation: G(i)1-alpha remained undetectable, G(i)2-alpha and G(i)3-alpha were both present on days 12 and 21. Of significance was the increase (160%) in the amount of G(i)2-alpha at midgestation (day 12) compared to days 0 and 21. A different pattern was observed with G(i)3-alpha which decreased with advancing gestation (day 0 > 12 > 21). Immunodetection of beta subunits of G proteins indicated the presence of a 35/36 kDa doublet on days 0, 12 and 21, with an increase at midgestation. The simultaneous increase in G(i)2-alpha and beta subunits may provide an explanation for the previously demonstrated alteration in adenylate cyclase stimulability detected at midgestation.