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

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.