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Departments of 1 Pharmacology and Toxicology and 2 Medicine, and 3 Robarts Research Institute, University of Western Ontario, London, Ontario, Canada N6A 5C1
Isolated myenteric
ganglion networks were used in a perifusion protocol to characterize
the response of interstitial adenosine levels to changes in prevailing
PO2. The biological activity of such
adenosine was assessed using inhibition of release of substance P (SP)
as a functional measure of adenosine activity, and the effect of
altered O2 tension on both
spontaneous and elevated extracellular
K+ concentration-evoked SP release
from networks was determined over a range of
PO2 values from hypoxic
(PO2 = 54 mmHg) to hyperoxic
(PO2 = 566 mmHg). Release of SP was
found to be sensitive to PO2, and a
linear graded relationship was obtained. Perifusion in the additional
presence of the adenosine
A1-receptor-selective antagonist
1,3-dipropyl-8-cyclopentylxanthine (DPCPX) revealed considerable
adenosinergic inhibition with an inverse exponential relationship and
hyperoxic threshold PO2. Disinhibition of evoked SP release by DPCPX in the absence of TTX was
double that observed in its presence, indicating a neural source for
some of the adenosine released during hypoxia. A postulated neuroprotective role for adenosine is consistent with the demonstrated relationship between interstitial adenosine and prevailing
O2 tension.
enteric nerves; hypoxia; neuroprotection
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