Action potential blockade and contractions of the longitudinal muscle of the jejunum. Effects of tetrodotoxin (TTX) on cholinergic contractions of the jejunum of ground squirrel fed either a low (0.027%; A & C) or a high (1%; B & D) cholesterol diet. The animals were treated with either vehicle (A & B) or tegaserod (C & D). The action potential blocker tetrodotoxin (TTX; 10-7M) was added to the jejunal tissue segments 10 min before constructing a cumulative dose-response curve to the cholinergic agonist, carbachol. * TTX greater than No TTX (P < 0.05). N = 8–9.