Regional differences in cholinergic activity of muscle fibers from the human gastroesophageal junction

Muscles of the gastroesophageal junction that contribute to the lower esophageal sphincter (LES) include clasplike semicircular fibers on the right and slinglike oblique gastric fibers on the left. This study examined whether in vitro differences between the sling and clasp muscles could account for the in vivo asymmetry of LES pressure and its cholinergic contribution. Isometric tension was recorded from muscle strips of the sling, clasp, and circular layers of the esophagus and gastric fundus isolated from surgical specimens. The sling developed less spontaneous tension (8.9 +/- 4.3 mN/mm2) than the clasp (25.0 +/- 7.4 mN/mm(2), P < 0.01) but showed a fivefold greater increase in response to carbachol. Eserine (I mu M) increased tension in the sling muscle (64.5 +/- 29.7%), but not in the clasp, whereas I mu M atropine or I mu M tetrodotoxin had no significant effect in either muscle. In both muscles, tension was reduced by 10 mu M sodium nitroprusside. Sling or clasp muscle differed from circular muscle of the esophagus or gastric fundus in spontaneous tension, carbachol response, or responses to electrical stimulation. Thus the clasp muscle develops greater spontaneous tension, whereas the sling is more sensitive to cholinergic stimulation, providing a potential explanation for the in vivo asymmetry of the LES pressure and its response to cholinergic blockade.