INVOLVEMENT OF G(ALPHA-Q 11) IN THE CONTRACTILE SIGNAL-TRANSDUCTION PATHWAY OF MUSCARINIC M(3) RECEPTORS IN CECAL SMOOTH-MUSCLE/

The nature of the pertussis toxin-insensitive G-protein involved in mu scarinic-mediated phosphoinositides breakdown and contraction of isola ted smooth muscle cells from the circular layer of the rabbit caecum w as investigated. Immunoblotting of membrane proteins using affinity pu rified antibodies directed against different G-protein alpha-subunits revealed the expression of G(alpha q/11), G(alpha il) and G(alpha i2) in these cells. The carbachol-mediated [H-3]inositol phosphates accumu lation in saponin-permeabilized cells was abolished by anti-G(alpha q/ 11)-antibodies whereas anti-G(alpha il,2)-antibodies were ineffective. Moreover, the carbachol-induced contraction of permeabilized cells, a s determined by videomicrocopic measurements, was reversed by anti-G(a lpha q/11)-antibodies bur not affected by anti-G(alpha il,2)-antibodie s. From these data, we conclude that carbachol stimulates phosphoinosi tides hydrolysis and cell contraction through activation of specific m uscai inic M(3) receptors coupled to the peaussis toxin-insensitive G( alpha q/11)-protein. This is the first demonstration of (alpha q/11) i mplication in the contractile signal transduction pathway of muscarini c M(3) receptors in smooth muscle cells.