Carbon dioxide-induced inhibition of mechanical activity in gastrointestinal smooth muscle preparations isolated from the guinea-pig





Mechanical responses of smooth muscle elicited by application of CO<sub>2</sub>-gas bubbled physiological salt solution (CO<sub>2</sub>-gas solution) were investigated in isolated stomach antrum and colon preparations of the guinea-pig. Circular smooth muscle preparations of both colon and stomach were spontaneously active with periodic generation of phasic contractions. In colonic preparations, the CO<sub>2</sub>-gas solution produced a biphasic response, with an initial small transient contraction followed by a sustained inhibition of phasic contractions. Removal of the CO<sub>2</sub>-gas solution allowed a slow recovery of the spontaneous contractions over a period of about 40 min. The recovery developed with a similar time course irrespective of the length of time exposed to CO<sub>2</sub>-gas solution. The inhibitory responses elicited by CO<sub>2</sub>-gas solution were not modulated by atropine, N<sup>ω</sup>-nitro-L-arginine or neostigmine. Atropine-sensitive excitatory responses of smooth muscle elicited by transmural nerve stimulation or exogenously applied acetylcholine were attenuated or abolished in the presence of CO<sub>2</sub>-gas solution. In stomach preparations, the CO<sub>2</sub>-gas solution elicited a tri-phasic response, with an initial transient relaxation followed by a transient contraction and then a sustained inhibition of the rhythmic contractions. The peak amplitude of the transient contraction was about 2.5 times larger than the spontaneous phasic contractions. The pH of the CO<sub>2</sub>-gas solution was reduced to about 6. Application of pH 6 solution again produced a tri-phasic response, as was the case for the CO<sub>2</sub>-gas solution, however the amplitude of the transient contraction was only about 0.4 times that of the spontaneous contractions. The re-appearance of the abolished phasic contraction was quicker with the pH 6 solution (about 1.8 min) than it was for the CO<sub>2</sub>-gas solution (about 6 min). The inhibitory responses elicited by the CO<sub>2</sub>-gas solution could be simulated only partly by the acidified solution, and a possible involvement of additional factors in the inhibition elicited by CO<sub>2</sub>-gas solution was considered.<br>


  • Journal of smooth muscle research = 日本平滑筋学会機関誌

    Journal of smooth muscle research = 日本平滑筋学会機関誌 47(6), 167-182, 2011-12-01


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