1 We presently characterized the tachykinin receptor subtypes, using tachykinin receptor agonists and selective antagonists, that induce submucosal gland fluid flux (J(G)) from porcine tracheal explants with the hillocks technique. We also investigated the effects of the tachykinin receptor agonists on the electrophysiologic parameters of the tracheal epithelium in Ussing chambers. 2 The NK(1) tachykinin receptor agonist substance P (SP, 1 microM) and the NK(3) tachykinin receptor agonist [MePhe(7)]neurokinin B ([MePhe(7)]NKB, 1 microM) induced gland fluid fluxes of 0.29+/-0.03 microl min(-1) cm(-2) (n=26) and 0.36+/-0.05 microl min(-1) cm(-2) (n=24), respectively; while the NK(2) tachykinin receptor agonist [betaAla(8)]neurokinin A (4-10) ([betaAla(8)]NKA (4-10), 1 microM) had no effect on J(G) (n=10). 3 The NK(1) receptor antagonist CP99994 (1 microM, n=9) blocked 93% of the SP-induced J(G), whereas the NK(3) receptor antagonist SB223412 (1 microM, n=12) had no effect on the SP-induced J(G). However, SB223412 (1 microM, n=9) blocked 89% of the [MePhe(7)]NKB-induced J(G) while CP99994 (1 microM, n=10) did not affect the [MePhe(7)]NKB-induced J(G). The NK(2) receptor antagonist SR48968 (1 microM) did not block the J(G) induced by either the NK(1) (n=4) or NK(3) (n=13) receptor agonists. 4 The nicotinic ganglionic acetylcholine receptor antagonist hexamethonium (1 microM) and the muscarinic acetylcholine receptor antagonist atropine (1 microM) also decreased the NK(3) receptor agonist-induced J(G) by 67% (n=10) and 71% (n=12), respectively. 5 The potential difference (PD), short-circuit current (I(SC)), and membrane resistance (R(M)) of the porcine tracheal epithelial membranes were not significantly affected by any of the neurokinin agonists or antagonists (1 microM, basolateral) used in this study, although SP and [betaAla(8)]NKA (4-10) induced a slight transient epithelial hyperpolarization. 6 These data suggest that NK(1) and NK(3) receptors induce porcine airway gland secretion by different mechanisms and that the NK(3) receptor agonists induced secretion is likely due to activation of prejunctional NK(3) receptors on parasympathetic nerves, resulting in acetylcholine-release. We conclude that tachykinin receptor antagonists may have therapeutic potential in diseases with pathophysiological mucus hypersecretion such as asthma and chronic bronchitis.
