Tris does not inhibit isolated vascular or intestinal smooth muscle contraction

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Abstract
There are conflicting reports on the effect of tris (hydroxymethyl) aminomethane (Tris) on smooth muscle contraction. The effect of substitution of Tris for HCO3- in physiological saline solution on smooth muscle contractility was investigated. Tris (25 mM) increased amplitude without changing frequency of spontaneous contractions in rat portal vein. Tris did not inhibit norepinephrine-induced contractions in rat portal vein and aorta or histamine-induced contractions in tenia coli. When pH of the Tris-buffered solution was lowered from the control value of 7.4 to 7.0, spontaneous contractions in portal vein as well as agonist-induced contractions in all of the above preparations were inhibited. Tris did not inhibit contractions induced by Ca in K-depolarized smooth muscle preparations if the Tris-buffered solution contained sufficient amounts of Na+ (as did HCO3--buffered solution). Evidently, Tris does not inhibit contractile responses of isolated vascular and intestinal smooth muscle preparations provided that the conditions other than the buffer system (especially pH of solution) are similar to those in HCO3--buffered solutions.