Aj. Sansum et al., EVIDENCE THAT P2X PURINOCEPTORS MEDIATE THE EXCITATORY EFFECTS OF ALPHA-BETA METHYLENE-ADP IN RAT LOCUS-COERULEUS NEURONS, Neuropharmacology, 37(7), 1998, pp. 875-885
Extracellular and whole-cell patch clamp recordings were used to study
the excitatory responses elicited by purine nucleotides in pontine sl
ices of the rat brain containing the locus coeruleus (LC). The P2 puri
noceptor agonists, alpha beta-methyleneadenosine 5'-triphosphate (alph
a beta meATP) and adenosine 5'-O-(2-thiodiphosphate) (ADP beta S), and
a novel purinoceptor agonist, alpha beta-methyleneadenosine 5'-diphos
phate (alpha beta meADP), elicited concentration-dependent increases i
n the spontaneous firing rate over the concentration range (1-300 mu M
). On vagus nerve or dorsal root preparations alpha beta meADP (100 mu
M) had no agonist activity. In the presence of both alpha beta meATP
(300 mu M), ADP beta S (300 mu M) elicited a further and significant i
ncrease in the firing rate of the LC neurones, whilst neither alpha be
ta meATP nor alpha beta meADP (300 mu M) elicited a further response.
The P2 purinoceptor antagonists, suramin (100 mu M) and pyridoxalphosp
hate-6-azophenyl-2',4'-disphonic acid (PPADS, 30 mu M), markedly atten
uated responses to all three agonists. Whole-cell recording of membran
e current showed that, at - 60 mV, alpha beta meATP and alpha beta meA
DP (both 100 mu M) elicited inward currents of a similar magnitude, wh
ilst the inward currents elicited by a lower concentration of ADP beta
S (30 mu M) were larger and faded in the presence of this agonist. In
the presence of tetrodotoxin and a combination of other neurotransmis
sion blockers, both alpha beta meATP and alpha beta meADP still produc
ed inward currents. Based on the known selectivity of the agonists use
d in this study, there appear to be two distinct P2 purinoceptor types
present on neurones in the LC, which correspond to the P2X and P2Y ty
pes. The responses elicited by alpha beta meADP appear to be mediated
through a putative P2X purinoceptor, although further work is required
to determine which P2X receptor subtype(s) are involved. (C) 1998 Els
evier Science Ltd. All rights reserved.