Release of radioactive purines from cat nictitating membrane labeled with 3H-adenine

Cat nictitating membranes were incubated with 1-2 x 10(-7) M 3H-adenine or 3H-adenosine for 1 h. A tissuebath ratio of about 15 was found for both compounds in intact and denervated membranes. In intact nictitating membranes sympathetic nerve stimulation (4 Hz, 5 min) caused a net release of purines (0.66 +/- 17% of the tissue content), which was reduced by alpha-blockade. Noradrenaline (1-3 microM) or tyramine 60 microM), which produced the same contractile response as did nerve stimulation, increased purine release to the same extent as did nerve stimulation. The effect of either agent was reduced or abolished by phentolamine. Purine release could also be induced by acetylcholine and ATP. This release was not altered after surgical denervation. There was an excellent correlation between the contractile response and the purine release induced by nerve stimulation, noradrenaline, tyramine and acetylcholine. However, ATP caused a larger release of 3H-purines than expected from the contractile responses, possibly indicating displacement. The results indicate that most if not all of the 3H-purines released by nerve stimulation in the cat nictitating membrane are derived from postjunctional elements.