Phasic and tonic types of smooth muscle activity in lower oesophageal sphincter and stomach of the dog.

Mechanical activity of isolated circular muscle strips from the lower oesophageal sphincter (LES), fundus, corpus and antrum of canine stomach was recorded. Nifedipine (10(-6) mol/l) selectively suppressed the phasic components of spontaneous, acetylcholine (ACh)- and noradrenaline (NA)-induced activity of gastric strips. The nifedipine-resistant tonic components of gastric strips were suppressed by nitroprusside sodium (NP) (10(-5) mol/l). LES strips exhibited only weak spontaneous activity. Their ACh-induced activation was nearly completely suppressed by nifedipine. Only NA was able to elicit a strong nifedipine-resistant activation which was, in contrast to the activation of fundus strips, not suppressed by NP.