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L ‐Citrulline inhibits [ 3 H]acetylcholine release from rat motor nerve terminals by increasing adenosine outflow and activation of A 1 receptors
Author(s) -
Barroso A,
Oliveira L,
CampesattoMella E,
Silva C,
Timóteo M A,
MagalhãesCardoso M T,
AlvesdoPrado W,
CorreiadeSá P
Publication year - 2007
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 - 10.1038/sj.bjp.0707242
Subject(s) - adenosine , citrulline , chemistry , adenosine deaminase , nitric oxide , arginine , adenosine a1 receptor , medicine , extracellular , adenosine receptor , endocrinology , nitroarginine , acetylcholine , nitric oxide synthase , biochemistry , receptor , biology , amino acid , agonist
Background and purpose: Nitric oxide (NO) production and depression of neuromuscular transmission are closely related, but little is known about the role of L‐citrulline, a co‐product of NO biosynthesis, on neurotransmitter release. Experimental approach: Muscle tension recordings and outflow experiments were performed on rat phrenic nerve‐hemidiaphragm preparations stimulated electrically. Key results: L‐citrulline concentration‐dependently inhibited evoked [ 3 H]ACh release from motor nerve terminals and depressed nerve‐evoked muscle contractions. The NO synthase (NOS) substrate, L‐arginine, and the NO donor, 3‐morpholinosydnonimine chloride (SIN‐1), also inhibited [ 3 H]ACh release with a potency order of SIN‐1>L‐arginine>L‐citrulline. Co‐application of L‐citrulline and SIN‐1 caused additive effects. NOS inactivation with N o ‐nitro‐L‐arginine prevented L‐arginine inhibition, but not that of L‐citrulline. The NO scavenger, haemoglobin, abolished inhibition of [ 3 H]ACh release caused by SIN‐1, but not that caused by L‐arginine. Inactivation of guanylyl cyclase with 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ) fully blocked SIN‐1 inhibition, but only partially attenuated the effects of L‐arginine. Reduction of extracellular adenosine accumulation with adenosine deaminase or with the nucleoside transport inhibitor, S‐( p ‐nitrobenzyl)‐6‐thioinosine, attenuated the effects of L‐arginine and L‐citrulline, while not affecting inhibition by SIN‐1. Similar results were obtained with the selective adenosine A 1 receptor antagonist, 1,3‐dipropyl‐8‐cyclopentylxanthine. L‐citrulline increased the resting extracellular concentration of adenosine, without changing that of the adenine nucleotides. Conclusions and implications: NOS catalyses the formation of two neuronally active products, NO and L‐citrulline. While, NO may directly reduce transmitter release through stimulation of soluble guanylyl cyclase, the inhibitory action of L‐citrulline may be indirect through increasing adenosine outflow and subsequently activating inhibitory A 1 receptors. British Journal of Pharmacology (2007) 151 , 541–550; doi: 10.1038/sj.bjp.0707242