COOLING-INDUCED CONTRACTION OF TRACHEA ISOLATED FROM NORMAL AND SENSITIZED GUINEA-PIGS

Fast (-7-degrees-C/min) cooling of guinea-pig isolated trachea produced a rapidly developing, transient contraction followed by relaxation. Cooling-induced contraction was dependent on temperature (30, 20 or 10-degrees-C) and responses in trachea obtained from actively sensitized guinea pigs were significantly greater (20 and 10-degrees-C) than those observed in normal trachea. Cooling to 20-degrees-C was selected for subsequent experiments. Pretreatment with sufficient concentrations of atropine, clemastine, cromoglycate, indomethacin, or nordihydroguaiaretic acid did not depress contraction to cooling in either normal or sensitized trachea. This indicates a direct effect of cooling. The contraction produced by cooling was resistant to verapamil (1-mu-mol/l) or dantrolene (0.3 mmol/l). Calmodulin antagonists (trifluoperazine, W-7 and calmidazolium; all of them at 10-100-mu-mol/l) inhibited contraction in sensitized and normal trachea. Activators of protein kinase C (phorbol 12,13-diacetate, 1-mu-mol/l) enhanced while inhibitors (H-7, 20-mu-mol/l; staurosporine, 10-mu-mol/l) depressed cooling-induced contraction in both normal and sensitized tissues. Incubation (20 min) in a Ca2+-free solution inhibited cooling-induced contraction in normal but not in sensitized trachea. Exposure to a low Na+ (25 mmol/l) or a K+-free medium abolished contraction to cooling in normal and sensitized trachea. Ouabain (0.1 - 10-mu-mol/l) and vanadate (0.01 - 5 mmol/l) inhibited cooling-induced contraction to a greater extent in normal than in sensitized trachea. Polymyxin B (0.5 mmol/l) selectively depressed responses to cooling in sensitized trachea. In a separate series of experiments, it was shown that sensitized trachea was hyperresponsive to ouabain and vanadate. Previous cooling to 20-degrees-C abolished responses to ouabain but only attenuated those to vanadate. These results are compatible with an enhancement of Na+, K+-ATPase and Ca2+-ATPase activities in sensitized trachea and further support the notion that intracellularly stored Ca2+ plays a decisive role in the activation of sensitized tracheal muscle.