Impaired Acetylcholine-induced Smooth Muscle Contraction in Colitis Involves Altered Calcium Mobilization and AKT Phosphorylation

In trinitrobenzene sulphonic acid (TNBS)-induced colitis in the rat, isolated circular smooth muscle cells (CSMC) show decreased contraction to acetylcholine (ACh) but the presence and contribution of altered intracellular signaling is poorly understood. To characterize ACh-induced signaling via calcium and the principal signaling kinases ERK1/2 and AKT in CSMC during colitis, isolated colonic CSMC from control, TNBS-inflamed (day 4) or recovered (day 36) rats were treated with ACh. Intracellular Ca2+ and contraction was determined by fluorescence video microscopy. Total and phosphorylated AKT and ERK1/2 were determined by western blotting. By day 4 of colitis, Ca2+ elevation was both delayed and reduced to less than threefold of control. The time to contraction after ACh was increased threefold, and peak contraction velocity was half that of control, with a marked reduction in calcium mobilization from intracellular stores. In control CSMC, ACh increased pAKT by sixfold over control at 5 s post application but without change in pERK1/2. Inhibition of AKT did not affect the Ca2+ response to ACh but reduced CSMC contraction by an amount similar to that seen in colitis. This, taken with a marked reduction of ACh-induced pAKT in CSMC in colitis, suggests that AKT signaling is an additional target of inflammation leading to impaired contraction.