Premium
Role of nitric oxide in non‐adrenergic, non‐cholinergic inhibitory junction potentials in canine ileocolonic sphincter
Author(s) -
Ward Sean M.,
McKeen Emma S.,
Sanders Kenton M.
Publication year - 1992
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1992.tb09056.x
Subject(s) - apamin , tetrodotoxin , hyperpolarization (physics) , phentolamine , inhibitory postsynaptic potential , chemistry , endocrinology , medicine , atropine , cholinergic , acetylcholine , nitric oxide , stimulation , membrane potential , nitric oxide synthase , excitatory postsynaptic potential , potassium channel , biology , biochemistry , stereochemistry , nuclear magnetic resonance spectroscopy
1 Electrical field stimulation causes neurally‐mediated relaxation of the ileocolonic sphincter that is due to activation of non‐adrenergic and non‐cholinergic (NANC) nerves. Recent studies have suggested that nitric oxide (NO) is the neurotransmitter that mediates relaxation. 2 Using intracellular recording techniques, we have tested whether NANC inhibitory junction potentials (i.j.ps) in the canine ileocolonic sphincter are also mediated by NO. 3 Electrical field stimulation elicited excitatory and inhibitory junction potentials: e.j.ps were blocked by atropine (10 −6 m ) and tetrodotoxin (TTX; 10 −6 m ); i.j.ps were also blocked by TTX and partially blocked by apamin (10 −6 m ). I.j.ps were unaffected by atropine, phentolamine and propranolol (all at 10 −6 m ). 4 The arginine analogues, l ‐N G ‐nitroarginine methyl ester ( l ‐NAME) and N G ‐monomethyl‐ l ‐arginine ( l ‐NMMA), decreased the amplitude of i.j.ps and l ‐arginine, but not d ‐arginine, partially restored the i.j.ps. 5 I.j.ps were also inhibited by oxyhaemoglobin (1%), but not by methaemoglobin. 6 Exogenous NO (10 −7 m to 3 × 10 −5 m ) caused concentration‐dependent hyperpolarizations that were similar in amplitude to the NANC nerve‐evoked i.j.ps. Hyperpolarizations to NO were unaffected by l ‐NAME, but were blocked by oxyhaemoglobin. 7 Tetrodotoxin, l ‐NAME and oxyhaemoglobin all caused depolarization of resting membrane potential. 8 The specific guanosine 3′:5′‐cyclic monophosphate phosphodiesterase inhibitor, M&B 22948, caused hyperpolarization, increased the maximum level of hyperpolarization reached during i.j.ps, and increased the duration of i.j.ps. 9 These data further support the hypothesis that NANC neurotransmission in the ileocolonic sphincter is mediated by NO or an NO‐releasing compound. The data also suggest that tonic release of NO, possibly from spontaneous firing of NANC nerves, may regulate resting membrane potential and tone in this sphincter.