Radioligand binding, autoradiographic and functional studies demonstrate tachykinin NK-2 receptors in dog urinary bladder

CJ Mussap, C Stamatakos and E Burcher

School of Physiology and Pharmacology, University of New South Wales, Sydney, Australia.

Tachykinin receptors in the dog bladder were characterized using radioligand binding, functional and autoradiographic techniques. In detrusor muscle homogenates, specific binding of [125l]iodohistidyl neurokinin A (INKA) and [125l]Bolton Hunter eledoisin was reversible, saturable and, to a single class of sites of Kd, 3,6 and 27 nM, respectively. No specific binding of [125l]Bolton Hunter[Sar9, Met (O2)11] substance P occurred. INKA binding was reduced by the peptidase inhibitor bacitracin. The rank potency order of agonists competing for binding of both radioligands indicated interaction at NK-2 sites. NK-2- selective antagonists also competed for INKA binding, with SR 48968, GR 94800, MDL 29913 and the selective agonist [Lys5, MeLeu9, Nle10]-NKA(4- 10) showing biphasic binding profiles. Autoradiographic studies revealed specific binding of INKA and [125l]Bolton Hunter eledoisin over detrusor muscle and small arteries. [125l]Bolton Hunter [Sar9, Met (O2)11] SP labeled the intima of arteries and arterioles, but not the detrusor muscle. Tachykinins contracted detrusor muscle strips, with potency order at the carbachol EC15 NKA = kassinin > [Lys5, MeLeu9, Nle10]-NKA(4-10) = neuropeptide gamma = neuropeptide K = NKB > > MDL 28564, with [Sar9, Met(O2)11]-SP ineffective. Shallow concentration- response curves, variable efficacies and inhibition by atropine and mepyramine suggest that other mechanisms may influence contractile responses. Responses to [Lys5, MeLeu9, Nle10]-NKA(4-10) were inhibited competitively by MDL 29913 and MEN 10207 (pA2 values: 6.4 and 5.3, respectively). Antagonism by SR 48968 and GR 94800 was noncompetitive (both pK8 values 8.9). In summary, NK-2-preferring ligands showed superior potency as both binding competitors and contractile agonists, demonstrating that NK-2 receptors mediate detrusor muscle contraction, similar to the human detrusor. Tachykinins may play important roles in the micturition reflex and in regulating detrusor muscle blood flow in the dog.

Volume 279, Issue 1, pp. 423-434, 10/01/1996
Copyright © 1996 by American Society for Pharmacology and Experimental Therapeutics

This article has been cited by other articles:

				R. Saban, N. P. Gerard, M. R. Saban, N.-B. Nguyen, D. J. DeBoer, and B. K. Wershil Mast cells mediate substance P-induced bladder inflammation through an NK1 receptor-independent mechanism Am J Physiol Renal Physiol, October 1, 2002; 283(4): F616 - F629. [Abstract] [Full Text] [PDF]