Effect of pH on Contractile Activity of Rabbit Intestinal Smooth Muscle With and Without Added Substrates

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Abstract
Spontaneous contractile activity of longitudinal smooth muscle of rabbit small intestine occurred at all pH.levels between 7.4 and 5.35. In media below pH 5.75 there was considerable depression of activity, which was not attributable to injury of the contractile system. With endogenous substrate or added pyruvic or acetate as the principal source of contraction energy, the amplitude and frequency were only moderately reduced with reduction of pH over the range 7.4 to 6.1; but with glucose, the amplitude was reduced markedly with reduction of pH. Measurements of the concns. of acetate and pyruvate necessary to produce half-maximal stimulation of amplitude of substrate depleted muscle at pH 7.4 and 7.1 led to the conculsion that the cell membrane was much more permeable to undissociated molecules than to ions of these substrates, but that at pH 7.4, the ions constitute well over 90% of these substrates transferred across the membrane. At pH 6.1 and 6.5 addition of high concns. of pyruvate, acetate, and propionate produced a temporary inhibition of contractile activity.

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