Pertussis toxin and N-ethylmaleimide inhibit histamine- but not calcium ionophore-induced endothelium-dependent relaxation

Endothelium-dependent relaxation of the guinea pig pulmonary artery induced by histamine was inhibited by preincubation of the tissue with 10 μM N-ethylmaleimide (NEM) for 10 min, whereas the endothelium-dependent relaxation induced by the calcium ionophore A 23187 was not affected by NEM. Pretreatment of the preparations with 0.2–1 μg/ml pertussis toxin for 120 min inhibited concentration-dependently the histamine-induced relaxation. In contrast, endothelium-dependent relaxation in response to the calcium ionophore A 23187 was not affected by pertussis toxin. Since NEM and pertussis toxin are thought to interfere with membrane located GTP binding proteins, it is suggested that such a coupling protein is involved in the signal transduction of the histamine receptor leading to endothelium-dependent relaxation.