Tachykinin NK3 and NK1 receptor activation elicits secretion from porcine airway submucosal glands

Abstract

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.

Figure 1

Effect of SP on submucosal gland secretion. The SP-induced gland secretion is inhibited in a dose-dependent manner by the NK₁-receptor antagonist CP99994 at 0.1 μM and 1 μM but was unaffected by the NK₃ antagonist SB224312. ^*P<0.05 compared to SP alone.

Figure 2

Effect of [MePhe⁷] NKB and senktide on porcine tracheal tissues. (a) Concentration-response curve to [MePhe⁷] NKB on porcine tracheal submucosal gland secretion (n=12 from six pigs at each concentration). (b) Effects of tachykinin NK₁ receptor antagonist CP99994 (1 μM), tachykinin NK₂ receptor antagonist SR48968 (1 μM), and tachykinin NK₃ receptor antagonist SB223412 (1 μM) on submucosal gland secretion induced by (1 μM) [MePhe⁷] NKB or senktide. The data are presented as mean±s.e.mean and were compared using paired student's t-tests. Asterisks indicate significant difference (P<0.05) from tissues of the same trachea treated with the respective tachykinin NK₃ receptor agonist alone.

Figure 3

Effect of atropine and hexamethonium on the NK₃ receptor agonist [MePhe⁷]NKB-induced gland secretion. ^*P<0.05 compared to [MePhe⁷]NKB alone.