Control of human airway smooth muscle: In vitro studies

1087, 1982.-An in vitro study of neural and myogenic control of human tracheal smooth muscle was undertaken. Over 80 % of these had active tension and 13 % had phasic contractile activity. Tonic and phasic activities were not reversed by in-domethacin, 5,8,11,14-eicosatetraynoic acid, methysergide, me-pyramine, atropine, or tetrodotoxin (TTX) but were blocked by the calcium antagonist verapamil. In some quiescent strips, tonic and/or phasic activity was induced by exposure to potas-sium-conductance blockers such as 4-aminopyridine (4-AP) and tetraethylammonium chloride (TEA). Electrical (field) stimu-lation resulted in frequency-dependent biphasic responses: an initial atropine-sensitive cholinergic contraction followed by a nonadrenergic relaxation. This biphasic response to low stimu-lus parameters (~0.5 ms, ~15 Hz) was blocked by TTX and scorpion venom and enhanced by 4-AP and TEA, consisten