Auxotonic contractile responses of rat tracheal and bronchial airway smooth muscle.
The purposes of the present study were to directly compare: (1) the degree of trachealis muscle shortening and changes in tracheal dimensions and (2) ACh-mediated auxotonic contraction of trachea and intraparenchymal bronchi. The auxotonic contractile properties of tracheal and bronchial airway smooth muscle were assessed from 1-2 mm thick tracheal sections and;1 mm thick lung slices using videomicrometry in vitro at 37 degrees C. Acetylcholine resulted in reductions in luminal area, perimeter, mean radius, length, and breadth (22.0, 10.0, 11.9, 10.7 and 12.0%, respectively). Trachealis muscle shortening reached a maximum of 39.8+/-4.3%. The K(+)channel blocker 4-aminopyridine significantly augmented the ACh-mediated reductions in tracheal luminal dimensions. In response to ACh (10(-3)m), reductions in bronchial dimensions were significantly greater than those of the trachea for luminal area, perimeter and mean radius (44.6 vs. 18.6, 32.0 vs. 8.0 and 28.9 vs. 9.9%, respectively). These data indicate that auxotonic contractile responses of rat tracheal smooth muscle differ from those previously reported in the dog and guinea pig, that ACh-mediated auxotonic contraction of tracheal smooth muscle is augmented by 4-aminopyridine, and that proportionate reductions in luminal dimensions in response to ACh are considerably greater for bronchial than tracheal airways.
van Lunteren
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Case Western Reserve University and Louis Stokes Cleveland Department of Veteran Affairs Medical Center, Cleveland, OH 44106-1782, USA. exv4@po.cwru.edu
Moyer
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D015761:4-Aminopyridine / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D046508:Culture Techniques; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000502:physiology*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014132:Trachea / Q000033:anatomy & histology / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology
D026902:Potassium Channel Blockers; D014665:Vasodilator Agents; D015761:4-Aminopyridine; D000109:Acetylcholine