Stimulation of adenosine A₁and A_2Areceptors by AMP in the submucosal plexus of guinea pig small intestine

Abstract

Actions of adenosine 5Ј-monophosphate (AMP) on electrical and synaptic behavior of submucosal neurons in guinea pig small intestine were studied with "sharp" intracellular microelectrodes. Application of AMP (0.3-100 M) evoked slowly activating depolarizing responses associated with increased excitability in 80.5% of the neurons. The responses were concentration dependent with an EC50 of 3.5 Ϯ 0.5 M. They were abolished by the adenosine A2A receptor antagonist ZM-241385 but not by pyridoxal-phosphate-6-azophenyl-2,4-disulfonic acid, trinitrophenyl-ATP, 8-cyclopentyl-1,3-dimethylxanthine, suramin, or MRS-12201220. The AMP-evoked responses were insensitive to AA-COCF3 or ryanodine. They were reduced significantly by 1) U-73122, which is a phospholipase C inhibitor; 2) cyclopiazonic acid, which blocks the Ca 2ϩ pump in intraneuronal membranes; and 3) 2-aminoethoxy-diphenylborane, which is an inositol (1,4,5)-trisphosphate receptor antagonist. Inhibitors of PKC or calmodulin-dependent protein kinase also suppressed the AMP-evoked excitatory responses. Exposure to AMP suppressed fast nicotinic ionotropic postsynaptic potentials, slow metabotropic excitatory postsynaptic potentials, and slow noradrenergic inhibitory postsynaptic potentials in the submucosal plexus. Inhibition of each form of synaptic transmission reflected action at presynaptic inhibitory adenosine A 1 receptors. Slow excitatory postsynaptic potentials, which were mediated by the release of ATP and stimulation of P2Y 1 purinergic receptors in the submucosal plexus, were not suppressed by AMP. The results suggest an excitatory action of AMP at adenosine A 2A receptors on neuronal cell bodies and presynaptic inhibitory actions mediated by adenosine A 1 receptors for most forms of neurotransmission in the submucosal plexus, with the exception of slow excitatory purinergic transmission mediated by the P2Y 1 receptor subtype. gastrointestinal tract; neurogastroenterology; enteric nervous system; synaptic transmission; purinergic receptors THE CELLULAR NEUROPHYSIOLOGY of purinergic receptors in the enteric nervous system (ENS), which encompasses both P1-and P2-type receptors, continues to be a focus of attention for neurogastroenterology. Adenosine is generally accepted as the ligand for the P1 receptor; ATP is the ligand for P2 receptors (1).P1 receptors are further classified as A 1 , A 2A , A 2B , and A 3 receptors according to their pharmacology, molecular sequences, and signal transduction pathways. Both A 2A and A 2B adenosine receptors are coupled through a G s protein to adenylate cyclase, elevation of cAMP, and stimulation of neuronal excitability. On the other hand, A 1 and A 3 adenosine receptors are negatively coupled to adenylate cyclase through the same G s protein (35, 43) and inhibit cAMP formation and neuronal excitability.In the ENS, adenosine acts as a presynaptic neuromodulator to influence the release of the inhibitory neurotransmitters norepinephrine and somatostatin (2, 53) and the excitatory neurotransmitters acetylcholine (ACh) and ...

Extracellular purines are biomarkers of neutrophilic airway inflammation

“…As adenosine levels did not correlate with markers of disease, the present authors would not anticipate that adenosine-mediated signalling would increase with neutrophilic inflammation, and the increased ATP to adenosine ratio might favour a more pro-inflammatory environment [20]. However, recently published evidence suggests that AMP may serve as an adenosine receptor agonist, either directly [48] or after conversion to adenosine at the epithelial surface [49]. Thus, increased adenosine receptor signalling, mediated through AMP, could modulate increased inflammation.…”

Differentiation of Intestinal Epithelial Cells Mediated by Cell Confluence and/or Exogenous Nucleoside Supplementation

“…In addition to the functions listed in the first paragraph of this discussion, NT and NS can bind to specific receptors present on plasma membranes and therefore activate signal transduction systems that modulate different cellular functions [Gao et al, 2007]. This type of signaling has been investigated in neurons, muscle and immune cells, demonstrating that some NT and NS have a higher specificity for one receptor subtype but can also activate other receptors at pathophysiological concentrations [Fredholm et al, 2001].…”

Purinergic receptors and synaptic transmission in enteric neurons

“…These effects are thought to be through the A 2A receptor, which couples positively with adenylyl cyclase and causes accumulation of cAMP. This is supported by the finding that exogenous AMP also acts at A 2A receptors to cause slow EPSP-like depolarizations [52]. Exogenous application of adenosine also causes a slow hyperpolarization in some AH neurons [53] through the A 1 receptor and inhibition of adenylyl cyclase [51,54].…”

“…Similarly, fast EPSPs are reduced in the presence of adenosine (Fig. 2a) or AMP, an effect blocked by A 1 receptor antagonists [51,52,54]. The mechanism underlying presynaptic A 1 receptor inhibition of transmitter release involves an inhibition of adenylyl cyclase or phospholipase C with one result being an increase in potassium conductance and/or a decrease in calcium conductance [58].…”