The intracellular pathway of the acetylcholine-induced contraction in cat detrusor muscle cells

1 The present study was aimed to investigate intracellular pathways involved in acetylcholine (ACh)-induced contraction in cat detrusor muscle cells 2 Contraction was expressed as per cent shortening of length of individually isolated smooth muscle cells obtained by enzymatic digestion. Dispersed intact and permeabilized cells were prepared for the treatment of drugs and antibody to enzymes, respectively. Using Western blot, we confirmed the presence of related proteins. 3 The maximal contraction to ACh was generated at 10(-11) M. This response was preferentially antagonized by M-3 muscarinic receptor antagonist p-fluoro-hexahydrosiladifenidol (rhoF-HSD) but not by the M, antagonist pirenzepine and the M, muscarinic receptor antagonist methoctramine. We identified G-proteins G(q/11), G(s), G(0), G(il), G(i2) and G(i3) in the bladder detrusor muscle. ACh-induced contraction was selectively inhibited by Gq/11 antibody but not to other G subunit. 4 The phosphatidylinositol-specific phospholipase C (PI-PLC) inhibitor neomycin reduced ACh-induced contraction. However, the inhibitors of the phospholipase D, the phospholipase A, and protein kinase C did not attenuate the ACh-induced contraction. ACh-induced contraction was inhibited by antibody to PLC-beta(1) but not PLC-beta(3) and PLC-gamma Thapsigargin or strontium, which depletes or blocks intracellular calcium release, inhibited ACh-induced contraction. Inositol 1,4,5-triphosphate (IP3) receptor inhibitor heparin reduced ACh-induced contraction. 5 These results suggest that in cat detrusor muscle contraction induced by ACh is mediated via M-3 muscarinic receptor-dependent activation of G(q/11) and PLC-beta(1) and IP3-dependent Ca2+ release.