Adenosine outflow and
adenosine and
adenine nucleotide content of hippocampal slices were evaluated under two different experimental conditions:
ischemia-like conditions and electrical stimulation (10 Hz). Five minutes of
ischemia-like conditions brought about an 8-fold increase in
adenosine outflow in the following 5 min during reperfusion, and a 2-fold increase in
adenosine content, a 43% decrease in
ATP, a 72% increase in
AMP and a 30% decrease in energy charge (EC) at the end of the ischemic period. After 10 min of reperfusion
ATP,
AMP and EC returned to control values, while the
adenosine content was further increased. Five minutes of electrical stimulation brought about an 8-fold increase in
adenosine outflow that peaked 5 min after the end of stimulation, a 4-fold increase in
adenosine content and an 18% decrease in tissue EC at the end of stimulation. After 10 min of rest conditions the
adenosine content and EC returned to basal values. The origin of extracellular
adenosine from
S-adenosylhomocysteine (SAH) was examined under the two different experimental conditions. The
SAH hydrolase inhibitor, adenosine-2,3-dialdehyde (10 microM), does not significantly modify the
adenosine outflow evoked by electrical stimulation or
ischemia-like conditions. This finding excludes a significant contribution by the transmethylation pathway to
adenosine extracellular accumulation evoked by an electrical or ischemic stimulus, and confirms that the most likely source of
adenosine is from
AMP dephosphorylation.