Gradient in the effects of ethyl alcohol on canine gastric antral circular muscles

The effects of ethyl alcohol on the electrical and mechanical activities of canine gastric antral circular muscle were studied. Recently it has been reported that the circular layer of the antrum is not homogenous in its electrical activity. Therefore, circular muscles from the regions adjacent to the myenteric and submucosal borders of the circular layer were studied separately to compare the actions of ethyl alcohol through the thickness of the circular layer. In the first series of experiments concentration-response data were collected to describe the effects of ethyl alcohol on the contractile activities of myenteric and submucosal muscles. The data show that ethyl alcohol is more effective as an inhibitor of myenteric contractions than submucosal contractions. Next, experiments were performed to determine the electrical mechanism responsible for the contractile effects. Circular cells of submucosal and myenteric regions were impaled, and the muscles were exposed to several concentrations of ethyl alcohol ranging from 0.1 to 1.5%. Slow wave activity was reduced in frequency and amplitude in both regions. The inhibitory effect of ethyl alcohol on electrical activity was greater in submucosal muscles, but mechanical activity was less affected in these muscles because excitation-contraction coupling occurs at more polarized levels in the submucosal portion of the circular layer.