Bilateral ureteral obstruction alters levels of the G-protein subunits G_αs and G_αq/11

To evaluate the effects of bilateral ureteral obstruction (BUO) on the levels of G-protein subunits in glomeruli, we examined the types and amounts of G-protein subunits in glomerular membranes from sham-operated control (SOC) rats and rats with BUO of 24 hours duration utilizing bacterial toxin-catalyzed ADP-ribosylation and specific antibodies. ADP-ribosylation catalyzed by cholera or pertussis toxin demonstrated the presence of G_s and G_i proteins in glomerular membranes. Immunoblots further revealed the existence of two types of G_αs (45 and 52 kDa), as well as G_αi2 (40 kDa), G_αi3 (41 kDa), G_αq/11 (42 kDa) and G_β (35 to 36 kDa) in glomerular membranes. The predominant subspecies of G_αs was the 52 kDa protein. Detectable amounts of G_αo were not found in glomerular membranes. Moreover, G-protein subunits were not detected in cytosolic extracts of glomeruli. Both forms of G_αs and G_αq/11 were significantly reduced in glomerular membranes from rats with BUO when compared to SOC rats. No significant difference in total G_αi, G_αi2 and G_αi3 and G_β content was observed between the two groups of rats. In vivo pretreatment of rats with simultaneous administration of the angiotensin-converting enzyme inhibitor, enalaprilat, and the thromboxane synthase inhibitor, OKY-046, maintained the amount of G_αs and G_αq/11 in rats with BUO at the levels seen in SOC rats. The two drugs did not affect the amounts of G-protein subunits in glomerular membranes of SOC rats. We conclude that the decreased mass of two forms of G_αs and G_αq/11 in glomerular membranes from rats with BUO of 24 hours duration is caused by elevated levels of angiotensin II, thromboxane A₂, or both, that occur as a consequence of obstruction. This decrease in G_αs and G_αq/11 content may contribute in part to the changes in glomerular function present at 24 hours after the onset of bilateral ureteral obstruction.