The regulation of veratridine-stimulated electrogenic ion transport in mouse colon by neuropeptide Y (NPY), Y 1 and Y 2 receptors

Abstract

1. Neuropeptide Y (NPY) is a prominent enteric neuropeptide with prolonged antisecretory effects in mammalian intestine. Veratridine depolarises neurons consequently causing epithelial anion secretion across mouse colon mucosa. Our aim was to characterise functionally, veratridine-stimulated mucosal responses and to determine the roles for NPY, Y 1, and Y 2 receptors in modulating these neurogenic effects. 2. Colon mucosae (with intact submucous innervation) from wild-type mice (+/+) and knockouts lacking either NPY (NPY-/-), Y 1-/- or Y 2-/- were placed in Ussing chambers and voltage clamped at 0mV. Veratridine-stimulated short-circuit current (I sc) responses in +/+, Y 1 or Y 2 antagonist pretreated +/+ colon, Y 1-/- and NPY-/- colon were insensitive to cholinergic blockade by atropine (At; 1 μM) and hexamethonium (Hex; 10 μM). Tetrodotoxin (TTX, 100 nM) abolished veratridine responses, but had no effect upon carbachol (CCh) or vasoactive intestinal polypeptide (VIP)-induced secretory responses. 3. To establish the functional roles for Y 1 and Y 2 receptors, +/+ tissues were pretreated with either the Y 1 or Y 2 receptor antagonist (BIBO3304 (300 nM) or BIIE0246 (1 μM), respectively) and veratridine responses were compared with those from Y 1-/- or Y 2-/- colon. Neither BIBO3304 nor Y 1-/- altered veratridine-induced secretion, but Y 1 agonist responses were abolished in both preparations. In contrast, the Y 2 antagonist BIIE0246 significantly amplified veratridine responses in +/+ mucosa. Unexpectedly, NPY-/- colon exhibited significantly attenuated veratridine responses (between 1 and 5 min). 4. We demonstrate that electrogenic veratridine responses in mouse colon are noncholinergic and that NPY can act directly upon epithelia, a Y 1 receptor effect. The enhanced veratridine response observed in +/+ tissue following BIIE0246, indicates that Y 2 receptors are located on submucosal neurons and that their activation by NPY will inhibit enteric noncholinergic secretory neurotransmission. 5. We also demonstrate Y 1 and Y 2 receptor-mediated antisecretory tone in +/+ colon and show selective loss of each in Y 1 and Y 2 null colon respectively. In NPY-/- tissue, only Y 1-mediated tone was present, this presumably being mediated by endogenous endocrine peptide YY. Y 2 tone was absent from NPY-/- (and Y 2-/-) colon and we conclude that NPY activation of neuronal Y 2 receptors attenuates secretory neurotransmission thereby providing an absorptive electrolyte tone in isolated colon. © 2005 Nature Publishing Group All rights reserved.