title: Adenosine A₁ and A₂A receptor-mediated modulation of acetylcholine release in the mice neuromuscular junction.
abstract: Immunocytochemistry shows that purinergic receptors (P1Rs) type A1 and A2A (A1 R and A2 A R, respectively) are present in the nerve endings at the P6 and P30 Levator auris longus (LAL) mouse neuromuscular junctions (NMJs). As described elsewhere, 25 μm adenosine reduces (50%) acetylcholine release in high Mg(2+) or d-tubocurarine paralysed muscle. We hypothesize that in more preserved neurotransmission machinery conditions (blocking the voltage-dependent sodium channel of the muscle cells with μ-conotoxin GIIIB) the physiological role of the P1Rs in the NMJ must be better observed. We found that the presence of a non-selective P1R agonist (adenosine) or antagonist (8-SPT) or selective modulators of A1 R or A2 A R subtypes (CCPA and DPCPX, or CGS-21680 and SCH-58261, respectively) does not result in any changes in the evoked release. However, P1Rs seem to be involved in spontaneous release (miniature endplate potentials MEPPs) because MEPP frequency is increased by non-selective block but decreased by non-selective stimulation, with A1 Rs playing the main role. We assayed the role of P1Rs in presynaptic short-term plasticity during imposed synaptic activity (40 Hz for 2 min of supramaximal stimuli). Depression is reduced by micromolar adenosine but increased by blocking P1Rs with 8-SPT. Synaptic depression is not affected by the presence of selective A1 R and A2 A R modulators, which suggests that both receptors need to collaborate. Thus, A1 R and A2 A R might have no real effect on neuromuscular transmission in resting conditions. However, these receptors can conserve resources by limiting spontaneous quantal leak of acetylcholine and may protect synaptic function by reducing the magnitude of depression during repetitive activity.
authors.affiliation: Unitat d'Histologia i Neurobiologia (UHN), Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, Reus, Spain.
authors.forename: Neus
authors.initials: N
authors.lastname: Garcia
authors.forename: Mercedes
authors.initials: M
authors.lastname: Priego
authors.forename: Teresa
authors.initials: T
authors.lastname: Obis
authors.forename: Manel M
authors.initials: MM
authors.lastname: Santafe
authors.forename: Marta
authors.initials: M
authors.lastname: Tomàs
authors.forename: Nuria
authors.initials: N
authors.lastname: Besalduch
authors.forename: M Angel
authors.initials: MA
authors.lastname: Lanuza
authors.forename: Josep
authors.initials: J
authors.lastname: Tomàs
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D058907:Adenosine A1 Receptor Agonists / Q000494:pharmacology; D058916:Adenosine A1 Receptor Antagonists / Q000494:pharmacology; D058908:Adenosine A2 Receptor Agonists / Q000494:pharmacology; D058917:Adenosine A2 Receptor Antagonists / Q000494:pharmacology; D000818:Animals; D008297:Male; D051379:Mice; D009469:Neuromuscular Junction / Q000033:anatomy & histology / Q000378:metabolism / Q000502:physiology*; D043682:Receptor, Adenosine A1 / Q000187:drug effects / Q000378:metabolism*; D043705:Receptor, Adenosine A2A / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000502:physiology*
chemical_list: D058907:Adenosine A1 Receptor Agonists; D058916:Adenosine A1 Receptor Antagonists; D058908:Adenosine A2 Receptor Agonists; D058917:Adenosine A2 Receptor Antagonists; D043682:Receptor, Adenosine A1; D043705:Receptor, Adenosine A2A; D000109:Acetylcholine
keywords: cholinergic synapses; immunofluorescence; motor end-plate; motor nerve terminal; neurotransmission