3-Morpholinylsydnonimine inhibits glutamatergic transmission in rat rostral ventrolateral medulla via peroxynitrite formation and adenosine release.
We have previously reported that, depending on the dose, nitric oxide (NO)-generating agents exert a dual facilitatory and inhibitory action on glutamatergic transmission on the rostral ventrolateral medulla (RVLM) neurons. The molecular mechanisms underlying the NO-mediated synaptic inhibition have not yet been defined. Here we show that the amplitude of excitatory postsynaptic currents (EPSCs) was reversibly reduced by the NO donors 3-morpholinylsydnoneimine (SIN-1) (1 mM) and spermine NONOate (1 mM). This effect was antagonized by an active peroxynitrite decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl)prophyrinato iron (III) chloride, G(i/o)-coupled receptor blockers, N-ethylmaleimide and pertussis toxin, A(1) adenosine receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine, or adenosine deaminase. However, NO-sensitive guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, GABA(B) receptor antagonist (2S)-(+)-5,5-dimethyl-2-morpholineacetic acid (SCH50911), or cannabinoid receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride (SR141716A) had no effect on the inhibitory action of SIN-1 on EPSCs. Perfusion of adenosine mimicked and subsequently occluded the action of SIN-1. Inhibition of EPSC amplitude by SIN-1 was associated with an increase in the paired-pulse ratio of EPSCs. Furthermore, SIN reduced the frequency of spontaneous EPSCs without altering their amplitude of distribution. Pretreatment with N-type Ca(2+)-channel blocker omega-conotoxin GVIA selectively blocked SIN-1-induced inhibition of EPSCs. These results suggest that a higher dose of SIN-1 acts presynaptically to elicit a synaptic depression on the RVLM neurons through an inhibition of presynaptic N-type Ca(2+)-channel activity, leading to reduced glutamate release. The presynaptic action of SIN-1 is mediated by the formation of peroxynitrite, which subsequently acts to release adenosine to activate A(1) adenosine receptors.
Department of Pharmacology, College of Medicine, National Cheng Kung University, 1, Ta-Hsiue Road, Tainan 701, Taiwan.
Chiung-Chun
CC
Huang
Samuel H H
SH
Chan
Kuei-Sen
KS
Hsu
D000241:Adenosine / Q000378:metabolism*; D000818:Animals; D020864:Calcium Channels, N-Type / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects* / Q000502:physiology; D008981:Molsidomine / Q000031:analogs & derivatives / Q000494:pharmacology*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D030421:Peroxynitrous Acid / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology
D020864:Calcium Channels, N-Type; D020030:Nitric Oxide Donors; D030421:Peroxynitrous Acid; D018698:Glutamic Acid; C002385:linsidomine; D008981:Molsidomine; D000241:Adenosine