Some determinants of latency of off-response to electrical field stimulation in circular layer of smooth muscle of opossum esophagus.

Transverse strips from smooth muscle of opossum esophagus were subjected to electrical field stimulation of intramural nerves to study the latency of the off-response. Latency is the time from the end of the stimulus train to the beginning of the off-response. Latency increased from one end of the smooth muscle segment to the other; it was shortest proximally and longest distally. Variables altering this latency gradient were sought. Strip width and tension had no effect (P greater than 0.02). Longer stimulation trains shortened latency (P less than 0.02). Krebs solution was modified by changing potassium concentration and by the addition of: hexamethonium, 1 x 10(-4) M; D-tubocurarine, 1 x 10(-4) M; bethanechol, 5 x 10(-7) M; carbachol, 5 x 10(-7 M; physostigmine, 1 x 10(-7) M; propranolol, 1 x 10(-6) M; tolazoline, 5 x 10(6) M; norepinephrine, 1 x 10(-5) M; isoproterenol, 1 x 10(-6) M; and dopamine, 1 x 10(4) M. Increased potassium concentrations shortened latency, and decreased potassium concentrations lengthened it (P less than 0.02). Carbachol, bethanechol, physostigmine, and isoproterenol shortened latency (P less than 0.02). Hexamethonium, D-tubocurarine, tolazoline, propranolol, norepinephrine, and dopamine had no effect (P greater than 0.02).