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

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.