On the changes in the membrane potential and the contractile activity of the smooth muscle of the lower esophageal and ileo-caecal sphincters upon increased K in the nutrient solution.

The influence of increased K+ in the nutrient solution on the excitatory-contractile process in smooth-muscle strips from the lower esophageal sphincter (LES) and the ileo-caecal sphincter (ICS) of cats is studied. The changes in the membrane potential (MP) and the tension (T) are recorded by the sucrose gap method. The rise of the K+ concentration in the nutrient solution to 30 mM causes hyperpolarization and relaxation of LES, while in ICS depolarization is observed irrespective of the relaxation. In LES the higher K+ concentrations, as well as the isotonic K+ lead to initial brief hyperpolarization, followed by depolarization. A biphasic response in the contraction-relaxation and subsequent contraction corresponds to them. Irrespective of the fact that the response in ICS is also biphasic with respect to the contraction, the changes in MP are manifested only as depolarization. These responses of LES and ICS are not influenced by cholinergic and adrenergic blockers (atropinum sulfuricum, Propranolol, Phenoxybenzamine--(10(-6) to 10(-5) g/ml). In ouabaine-pretreated (10(-6) to 5 x 10(-6) M) smooth muscle from LES and ICS, in all K+ concentrations the response is depolarization and contraction. The effects of increased K+ in the nutrient solution on LES and ICS are connected with the ratio [K]i : [K]o ([K]i--intracellular, [K]o--extracellular). It is assumed that the Na-K pump in LES and ICS functions at a different level compared with the other smooth muscles of the gastro-intestinal tract.