Abstract
Abstract
Cooling of isolated guinea pig tracheal smooth muscle from 38 to 28°C over 2.25 min produced a transient contraction followed by sustained relaxation. The cooling-induced contraction was blocked either by pretreatment with ouabain at concentrations of 10-5 M or greater or by substitution of normal physiological salt solution with K-free solution. In contrast, the contractile response to cooling was not inhibited by pretreatment with phentolamine (10-5 M), atropine (10-5 M), tetrodotoxin (3 × 10-7 M), diphenhydramine (10-5 M), cromolyn sodium (10-3 M), indomethacin (3 × 10-7 M), nifedipine (10-7 M), or verapamil (3 × 10-6 M). Addition of NaHCO3 to the bath during cooling, preventing a change in pH of the physiological salt solution, did not affect the cooling-induced contraction. It is concluded that cooling of isolated guinea pig trachea produces a transient ouabain-sensitive contraction, and that the data suggest the contraction is mediated by inhibition of Na–K-ATPase in the smooth muscle rather than through neuronal stimulation or chemical mediator release.
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