HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 294/4/G1041    most recent 00356.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by McDonnell, B. Articles by Keef, K. D. Search for Related Content PubMed PubMed Citation Articles by McDonnell, B. Articles by Keef, K. D.

NEUROREGULATION AND MOTILITY

Functional evidence for purinergic inhibitory neuromuscular transmission in the mouse internal anal sphincter

Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada

Submitted 7 August 2007 ; accepted in final form 25 February 2008

The neurotransmitter(s) underlying nitric oxide synthase (NOS)-independent neural inhibition in the internal anal sphincter (IAS) is still uncertain. The present study investigated the role of purinergic transmission. Contractile and electrical responses to electrical field stimulation of nerves (0.1–5 Hz for 10–60 s) were recorded in strips of mouse IAS. A single stimulus generated a 28-mV fast inhibitory junction potential (IJP) and relaxation. The NOS inhibitor N-nitro-L-arginine (L-NNA) reduced the fast IJP duration by 20%. Repetitive stimulation at 2.5–5 Hz caused a more sustained IJP and sustained relaxation. L-NNA reduced relaxation at 1 Hz and the sustained IJP at 2.5–5 Hz. All other experiments were carried out in the presence of NOS blockade. IJPs and relaxation were significantly reduced by the P2 receptor antagonists 4-[[4-formyl-5-hydroxy-6-methyl-3-[(phosphonooxy)methyl]-2-pyridinyl]azo]-1,3-benzenedisulfonic acid (PPADS) (100 µM), by desensitization of P2Y receptors with adenosine 5'-[β-thio]diphosphate (ADP-βS) (10 µM), and by the selective P2Y1 receptor blocker 2'-deoxy-N⁶-methyl adenosine 3',5'-diphosphate (MRS2179) (10 µM). Relaxation and IJPs were also significantly reduced by the K⁺ channel blocker apamin (1 µM). Removal of extracellular potassium (K_o) increased IJP amplitude to 205% of control, whereas return of K_o 30 min later hyperpolarized cells by 19 mV and reduced IJP amplitude to 50% of control. Exogenous ATP (3 mM) relaxed muscles in the presence of TTX (1 µM) and hyperpolarized cells by 15 mV. In conclusion, these data suggest that purinergic transmission significantly contributes to NOS-independent neural inhibition in the mouse IAS. P2Y1 receptors, as well as at least one other P2 receptor subtype, contribute to this pathway. Purinergic receptors activate apamin-sensitive K⁺ channels as well as other apamin-insensitive conductances leading to hyperpolarization and relaxation.

gastrointestinal; enteric; motor inhibition; NANC transmission