Some features of the spasmogenic actions of acetylcholine and histamine in guinea‐pig isolated trachealis

Abstract

1 Intracellular electrophysiological recording showed that acetylcholine (1 μmol l⁻¹) and histamine (2 μmol l⁻¹) depolarized trachealis cells and often increased the frequency of slow waves. Higher concentrations of these agents caused greater depolarization and abolition of slow waves. Marked depolarization was often associated with the appearance of electrical ‘noise’. These electrical phenomena were accompanied by tonic tension development in a contiguous segment of trachea. 2 Electrical ‘noise’ and tension evoked by high concentrations of acetylcholine or histamine could be dissipated by washing the agonist from the tissue. Acetylcholine-induced ‘noise’ was resistant to tetrodotoxin (3 μmol l⁻¹) and to hexamethonium (1 mmol l⁻¹). 3 Neither acetylcholine (10–1,000 μmoll⁻¹) nor histamine (2–200 μmol l⁻¹) increased the lanthanum-resistant calcium fraction of muscle-containing strips of trachea. 4 It is concluded that, while developing tension under the influence of acetylcholine or histamine, trachealis cells depolarize markedly but there is relatively little cellular influx of Ca²⁺.