To investigate the effects of calcium antagonist verapamil on the contraction and relaxation of human lower esophageal sphincter (LES) clasp and sling fibers induced by acetylcholine(Ach).

LES was obtained from patients with superior and middle esophageal carcinoma, and muscles of esophageal body and gastric bottom were served as controls. After isolation of muscle bundles of esophageal body, gastric bottom, sling fibers and clasp fibers, in vitro muscle stripe intensity measurement technique was employed to determine the effects of verapamil (10^-3 mol/L) on the contraction and relaxation of these four muscle stripes induced by Ach(10^-6, 10^-5, 10^-4, 10^-3 , 10^-2 and 10^-1 mol/L).

The contraction of circular muscles of esophageal body and gastric bottom and clasp fibers was not significantly changed after verapamil intervention (t=0.896, P=0.372; t=0.331, P=0.741; t=0.324, P=0.747). However, the contraction of sling fibers was significantly decreased from (17.0±5.2) g to (14.7±6.6) g after verapamil intervention (t=2.294, P=0.023).

Verapamil partly blocks the contraction of LES, and results in the relaxation of LES.