Impact of disrupting adenosine A₃ receptors (A₃⁻/⁻ AR) on colonic motility or progression of colitis in the mouse

Pharmacological studies suggest that adenosine A&sub3;AR influences motility and colitis. Functional A&sub3;⁻/⁻AR knockout mice were used to prove whether A&sub3;AR activation is involved in modulating either motility or colitis.

Functional disruption of A&sub3;AR in A&sub3;⁻/⁻AR mice alters intestinal motility. We postulate that ongoing release of adenosine and activation of presynaptic-inhibitory A&sub3;AR can slow down transit and inhibit the defecation reflex. A&sub3;AR may be involved in gliotransmission. In separate studies, A&sub3;⁻/⁻AR protects against DSS colitis, consistent with a novel hypothesis that A&sub3;AR activation contributes to development of colitis.

A&sub3;AR was probed by polymerase chain reaction (PCR) genotyping, Western blot, and immunochemistry. Motility was assessed in vivo by artificial bead-expulsion, stool-frequency, and FITC-dextran transit. Colitis was induced with dextran sodium sulfate (DSS) in A&sub3;⁻/⁻AR or wildtype (WT) age- and sex-matched controls. Progression of colitis was evaluated by histopathology, changes in myeloperoxidase (MPO), colon length, CD4(+) -cells, weight-loss, diarrhea, and the guaiac test.

Goat anti-hu-A&sub3; antiserum identified a 66 kDa immunogenic band in colon. A&sub3;AR-immunoreactivity is expressed in SYN(+) -nerve varicosities, s-100(+) -glia, and crypt cells, but not 5-HT(+) (EC), CD4(+) (T), tryptase(+) (MC), or muscle cells. A&sub3;AR immunoreactivity in myenteric ganglia of distal colon >> proximal colon by a ratio of 2:1. Intestinal transit and bead expulsion were accelerated in A&sub3;⁻/⁻AR mice compared to WT; stool retention was lower by 40%-60% and stool frequency by 67%. DSS downregulated A&sub3;AR in epithelia. DSS histopathology scores indicated less mucosal damage in AA&sub3;⁻/⁻AR mice than WT. A&sub3;⁻/⁻AR phenotype protected against DSS-induced weight loss, neutrophil (MPO), or CD4(+) -T cell infiltration, colon shortening, change in splenic weight, diarrhea, or occult-fecal blood. Conclusions: Functional disruption of A&sub3;AR in A&sub3;⁻/⁻AR mice alters intestinal motility. We postulate that ongoing release of adenosine and activation of presynaptic-inhibitory A&sub3;AR can slow down transit and inhibit the defecation reflex. A&sub3;AR may be involved in gliotransmission. In separate studies, A&sub3;⁻/⁻AR protects against DSS colitis, consistent with a novel hypothesis that A&sub3;AR activation contributes to development of colitis.