Effects of five different organic calcium antagonists on guinea‐pig isolated trachea

Abstract

The relaxant effects of five organic calcium antagonists (nicardipine, diltiazem, PY 108068, verapamil and bepridil) on guinea‐pig isolated trachea were tested against contractions induced by acetylcholine, histamine, 5‐hydroxytryptamine, potassium chloride (KCl) and tetraethylammonium (TEA) in a medium containing the normal amount of calcium and against calcium dose‐response curves in a calcium‐free, potassium‐enriched medium. These effects were compared with those of spasmolytic or specific acetylcholine or histamine antagonists. In contrast to the other drugs tested, organic calcium antagonists exerted a specific inhibitory effect on KCl‐ and TEA‐induced contractions. Their degree of activity was in the order: nicardipine > diltiazem > PY 108068 > verapamil > bepridil. All calcium antagonists inhibited calcium dose‐response curves at similar concentrations. Organic calcium antagonists therefore seem to exert a specific inhibitory effect on depolarizing agents in the guinea‐pig isolated trachea, unlike other tissues, notably some vascular smooth muscles. 1984 British Pharmacological Society