Uptake and release of [3H]adenosine in human dental pulp

The purpose of this study was to examine the uptake and release of adenosine in human dental pulp. Pulp was removed from extracted teeth and incubated in [3H]adenosine (0.02-3.2 micromol/l) for 30-90 min, washed for 30 min and the residual [3H]adenosine extracted and assayed. At 0.02 and 0.4 micromol/l the uptake was saturated after 30 min, whereas at 3.2 micromol/l it was not, even after 90 min. Destruction of the sympathetic nerves by 6-hydroxydopamine prior to incubation in [3H]adenosine (0.4 micromol/l) decreased the uptake of [3H] by 40%. Addition of S(4-nitrobenzyl)-6-thioguanosine (NBTG; 0.1 micromol/l), an inhibitor of adenosine uptake, blocked 90% of the uptake. Electrical stimulation of sympathetic nerves following incubation of pulp in [3H]adenosine (0.4 micromol/l) increased the overflow of [3H] into the medium superfusing the tissue segments. NBTG (0.1 micromol/l) had no effect on this overflow, whereas denervation with 6-hydroxydopamine prior to incubation decreased the overflow by 85%. Although the contribution of post-junctional elements, such as smooth muscle, to this release was not determined it is proposed that most of the purine released was derived from sympathetic nerves.