The inhibitory action of acetaldehyde on the tonic component of the potassium-induced contracture in the guinea-pig taenia caeci.

The effect of acetaldehyde on the contractile responses induced by potassium-rich solution was studied in the guinea-pig taenia caeci. Acetaldehyde at a concentration between 1 and 50 mM reduced the tonic contraction induced by a high potassium solution containing a normal concentration of CaCl2 without affecting the phasic one. The phasic contraction was depressed only slightly at a very high concentration of acetaldehyde (100 mM). The tonic component increased with increasing external Ca concentration, and the reduction of this tonic contraction by acetaldehyde was greater at high Ca concentrations. In Ca-free, K-rich solution, carbachol induced a transient contraction. This carbachol-induced contraction in the absence of external Ca was markedly depressed at the second application of carbachol, but it reappeared after exposure to a Ca-containing solution. In this condition acetaldehyde did not affect these carbachol-responses, while it decreased a slow rise of tension during exposure of Ca. These results suggest that acetaldehyde inhibits the entry of external calcium without having an appreciable effect on the release of Ca and on the filling of the internal stores with Ca.