Cyclic AMP in rat ileum: evidence for the presence of an extracellular cyclic AMP-adenosine pathway.
OBJECTIVE
Extracellular adenosine plays a relevant role in regulating intestinal motility and preventing inflammatory processes. Adenosine 3',5'-cyclic monophosphate (cAMP) extruded from cells may be converted to adenosine monophosphate and then to adenosine by ecto-phosphodiesterase and CD73/ecto-5'nucleotidase, respectively, thus representing a source of adenosine. Our purpose was to assess the existence of a functional extracellular cAMP-adenosine pathway in intestinal tissue, obtaining evidence for CD73 expression and evaluating the effect of cAMP on ileum motility.


METHODS
The formation of cAMP metabolites in rat ileum strips incubated with exogenous cAMP or [(3)H]cAMP was monitored by high-performance liquid chromatography. CD73 was detected by immunoprecipitation and immunofluorescence. The functional activity of exogenous cAMP on ileum strips was recorded by measuring tension changes.


RESULTS
In ileum strips, the generation of cAMP-derived adenosine monophosphate, adenosine, and inosine was time and concentration dependent and was blocked by phosphodiesterase or CD73 inhibitors in a manner consistent with exogenous cAMP being processed through the extracellular cAMP-adenosine pathway. Accordingly, [(3)H]cAMP uptake in ileum strips was negligible. Immunofluorescence revealed CD73 surface expression on intestinal smooth muscle cells and intact smooth muscle. Exogenous cAMP concentration-dependently increased ileum muscle tension partially inhibited by adenosine inactivation or receptor blockade. Forskolin-stimulated endogenous cAMP induced concentration-dependent ileum relaxations.


CONCLUSIONS
A functioning extracellular cAMP-adenosine pathway featuring CD73 expression is present in rat ileum and affects intestinal motility. Extracellular cAMP may therefore act on intestinal muscle both directly by binding to specific smooth muscle cell membrane sites and indirectly through its degradation products.
Giron
Maria Cecilia
MC
Department of Pharmacology and Anesthesiology, University of Padova, Padova, Italy. cecilia.giron@unipd.it
Bin
Anna
A
Brun
Paola
P
Etteri
Sabrina
S
Bolego
Chiara
C
Florio
Chiara
C
Gaion
Rosa Maria
RM
D015720:5'-Nucleotidase / Q000276:immunology / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism*; D019085:Fluorescent Antibody Technique, Direct; D019084:Fluorescent Antibody Technique, Indirect; D005769:Gastrointestinal Motility / Q000187:drug effects / Q000502:physiology*; D007082:Ileum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D047468:Immunoprecipitation; D007537:Isometric Contraction / Q000187:drug effects / Q000502:physiology; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar
D002352:Carrier Proteins; D005576:Colforsin; D000242:Cyclic AMP; D015720:5'-Nucleotidase