EFFECTS OF PHORBOL 12,13-DIACETATE AND ITS INFLUENCE ON SPASMOGENIC RESPONSES IN NORMAL AND SENSITIZED GUINEA-PIG TRACHEA

We have studied the effects of phorbol 12,13-diacetate (PDA) and its i nfluence on a variety of spasmogenic responses in trachea isolated fro m normal and sensitized guinea-pigs. Tracheal preparations were denude d of epithelium, treated with indomethacin (2.8 mu M), and cooled to 2 0 degrees C. In these experimental conditions, tracheal strips contrac ted to PDA (0.1 nM-1 mu M). Contractions to PDA (1 mu M) were greater in sensitized tissues. In normal trachea, contractions to PDA (0.1 mu M) were depressed by H-7, 1-(5-isoquinolinyl-sulphonyl)-2-methylpipera zube, (50 mu M), amiloride (10 mu M), verapamil (10 mu M) and Ca2+-fre e exposure. Similar effects were obtained in sensitized trachea except that PDA-induced contraction was resistant to verapamil and Ca2+-free exposure. Cooling (20 degrees C) of normal trachea substantially depr essed the response to CaCl2 (in K+-depolarized tissues), KCl, histamin e and 5-hydroxytryptamine without affecting the spasm induced by acety lcholine. This inhibitory effect of cooling was not observed in sensit ized trachea. PDA. (0.1 mu M) did not affect spasmogenic responses at 37 degrees C but counteracted the inhibitory effect of cooling in norm al trachea. PDA had no effect on sensitized tissues. PDA (0.1-1 mu M) did not alter Ca2+-induced contraction of skinned normal and sensitize d trachea. These results support the hypothesis that intracellularly s tored Ca2+ plays an important role in the activation of sensitized tra cheal muscle.