Electromechanical effects of tetraethylammonium and K⁺ on histamine-induced contraction in pig isolated tracheal smooth muscle

Abstract

The effect of tetraethylammonium (TEA) and K⁺ on contractions to histamine and acetylcholine have been compared in the pig isolated trachea using organ bath and sucrose-gap techniques. Histamine elicited weak contractions, compared with acetylcholine; however, these contractions were markedly potentiated by pretreatment with TEA (10 mM) or by raising the external KCl concentration to 30–50 mM. Neither TEA nor K⁺ increased the sustained depolarization evoked by histamine (or acetylcholine) although oscillatory depolarizations were often observed in the presence of TEA. Verapamil and a zero Ca²⁺ Krebs solution reduced contractions to histamine and reduced or abolished the effect of TEA and K⁺ on histamine-induced contractions. The results unmask different mechanisms of contraction for histamine and acetylcholine. Histamine-induced tone appears to be linked with mechanisms sensitive to TEA and high K⁺, possibly involving increased translocation of Ca²⁺ across the plasma membrane.