The regulation of veratridine-stimulated electrogenic ion transport in mouse colon by neuropeptide Y (NPY), Y1 and Y2 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 0 mV. 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 microM) and hexamethonium (Hex; 10 microM). 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 microM), 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.