Regional characterization of G-protein subunits in glomeruli, cortices and medullas of the rat kidney

We examined the types of guanine nucleotide-binding regulatory (G) protein subunits in isolated glomeruli, cortices excluding glomeruli and medullas of rat kidneys using bacterial toxin-catalyzed adenosine 5'-diphosphate (ADP) ribosylation and specific immunoblots. ADP ribosylation catalyzed by cholera or pertussis toxin revealed the presence of stimulatory G (Gs) or inhibitory G (Gi) proteins in membranes of the 3 segments of the kidney. Immunoblots further demonstrated the existence of several G-protein subunits, two G(s)-protein α-subunits (G(αs)):45 and 52 kD), G(i)-protein α₁, α₂ and α₃-subunits (G(αi1),G(αi2):40-41 kD, G(αi3): 40 kD), bacterial toxin-insensitive G-protein α(q)- and α₁₁-subunits (G(αq/11): 42 kD) and G-protein β-subunits (G(β): 35-36 kD), in membranes of the preparations. The predominant subspecies of G(αs) was a 52-kD protein in glomerular membranes and a 45-kD protein in membranes of cortices and medullas. All of the G-protein subunits examined, however, were not detected in cytosolic fractions of glomeruli, cortices and medulas. Thus, we conclude that detectable quantities of several G-protein subunits including the new G-protein subunit, G(αq/11), are present in membranes of glomeruli, cortices not containing glomeruli and medullas from the rat kidney. Both the existence of G(ai1) and/or G(ai2) subunits in glomeruli and the presence of G(αq/11) subunits in the 3 preparations are new evidence. Moreover, the current study indicates the existence of the predominant subspecies of G(αs) subunits in the 3 distinct segments of the rat kidney.