title: Induction of a myogenic response in tonic airway smooth muscle by tetraethylammonium.
abstract: In multi-unit tracheal smooth muscle (TSM), quick stretches applied at a velocity of 5 times the measured maximum velocity of isotonic shortening of the muscle, of a magnitude 3 times the measured extension of the series-elastic component when the muscle contracts maximally, and at optimal muscle length (L-o) were unable to elicit any myogenic response (MR). Experimental conditions such as hypoxia (P-O2 smaller than 60 mmHg) and acidosis (pH equals 6.8) or the presence of Ba2+ (2 mM), acetylcholine (10-6 M), or high (K+)-o (59 mM) were also unable to elicit the MR. However, tetraethylammonium chloride (TEA, 0.4-67 mM) produces 1) spontaneous phasic contractions and 2) a MR to quick stretch. The ionic basis for these changes was then investigated by studying the Ca and Mg dependence of the response to TEA. The dose-response relationship to TEA was shifted to the left by decreasing external Mg2+ from 2.5 to 0.5 mM. The ability of TSM to produce a MR was absolutely dependent on external Ca, but the threshold concentration required shifted from 2.5 times 10-5 M at normal external Mg (2.5 mM) to 5 times 10-4 M at the reduced external Mg (0.5 mM). The effects of TEA on spontaneity and the MR were abolished by D-600. These results suggest that 1) TEA functionally converts multiunit smooth muscle into a single unit one and leads to the development of a MR and 2) the MR results from a depolarization-activated mobilization of Ca and is inhibited by ionic conditions known to increase membrane permeability.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D001696:Biomechanical Phenomena; D002118:Calcium / Q000494:pharmacology; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D010812:Physical Stimulation; D011188:Potassium / Q000494:pharmacology; D013757:Tetraethylammonium Compounds / Q000494:pharmacology*; D014132:Trachea / Q000502:physiology*; D014159:Transducers
chemical_list: D013757:Tetraethylammonium Compounds; D001464:Barium; D008274:Magnesium; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium