PAP and NT5E inhibit nociceptive neurotransmission by rapidly hydrolyzing nucleotides to adenosine.
BACKGROUND
Prostatic acid phosphatase (PAP) and ecto-5'-nucleotidase (NT5E, CD73) produce extracellular adenosine from the nucleotide AMP in spinal nociceptive (pain-sensing) circuits; however, it is currently unknown if these are the main ectonucleotidases that generate adenosine or how rapidly they generate adenosine.


RESULTS
We found that AMP hydrolysis, when measured histochemically, was nearly abolished in dorsal root ganglia (DRG) neurons and lamina II of spinal cord from Pap/Nt5e double knockout (dKO) mice. Likewise, the antinociceptive effects of AMP, when combined with nucleoside transport inhibitors (dipyridamole or 5-iodotubericidin), were reduced by 80-100% in dKO mice. In addition, we used fast scan cyclic voltammetry (FSCV) to measure adenosine production at subsecond resolution within lamina II. Adenosine was maximally produced within seconds from AMP in wild-type (WT) mice but production was reduced >50% in dKO mice, indicating PAP and NT5E rapidly generate adenosine in lamina II. Unexpectedly, we also detected spontaneous low frequency adenosine transients in lamina II with FSCV. Adenosine transients were of short duration (<2 s) and were reduced (>60%) in frequency in Pap-/-, Nt5e-/- and dKO mice, suggesting these ectonucleotidases rapidly hydrolyze endogenously released nucleotides to adenosine. Field potential recordings in lamina II and behavioral studies indicate that adenosine made by these enzymes acts through the adenosine A1 receptor to inhibit excitatory neurotransmission and nociception.


CONCLUSIONS
Collectively, our experiments indicate that PAP and NT5E are the main ectonucleotidases that generate adenosine in nociceptive circuits and indicate these enzymes transform pulsatile or sustained nucleotide release into an inhibitory adenosinergic signal.
Department of Cell and Molecular Physiology, University of North Carolina, CB #7545, Chapel Hill, North Carolina 27599, USA.
Sarah E
SE
Street
Paul L
PL
Walsh
Nathaniel A
NA
Sowa
Bonnie
B
Taylor-Blake
Thomas S
TS
Guillot
Pirkko
P
Vihko
R Mark
RM
Wightman
Mark J
MJ
Zylka
D015720:5'-Nucleotidase / Q000235:genetics / Q000378:metabolism*; D000135:Acid Phosphatase; D000241:Adenosine / Q000378:metabolism*; D000249:Adenosine Monophosphate / Q000378:metabolism; D000818:Animals; D004176:Dipyridamole / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D059225:Nociception / Q000187:drug effects; D009711:Nucleotides / Q000378:metabolism*; D010146:Pain / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism*; D043682:Receptor, Adenosine A1 / Q000235:genetics / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects / Q000235:genetics; D014372:Tubercidin / Q000031:analogs & derivatives / Q000494:pharmacology
D009711:Nucleotides; D043682:Receptor, Adenosine A1; C034214:5-iodotubercidin; D000249:Adenosine Monophosphate; D004176:Dipyridamole; D000135:Acid Phosphatase; C428439:prostatic acid phosphatase; D017027:Protein Tyrosine Phosphatases; D015720:5'-Nucleotidase; D000241:Adenosine; D014372:Tubercidin