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 th e right and slinglike oblique gastric fibers on the left. This study e xamined whether in vitro differences between the sling and clasp muscl es could account for the in vivo asymmetry of LES pressure and its cho linergic contribution. Isometric tension was recorded from muscle stri ps of the sling, clasp, and circular layers of the esophagus and gastr ic fundus isolated from surgical specimens. The sling developed less s pontaneous tension (8.9 +/- 4.3 mN/mm2) than the clasp (25.0 +/- 7.4 m N/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 mu scles, tension was reduced by 10 mu M sodium nitroprusside. Sling or c lasp muscle differed from circular muscle of the esophagus or gastric fundus in spontaneous tension, carbachol response, or responses to ele ctrical stimulation. Thus the clasp muscle develops greater spontaneou s tension, whereas the sling is more sensitive to cholinergic stimulat ion, providing a potential explanation for the in vivo asymmetry of th e LES pressure and its response to cholinergic blockade.