Metabolism and presynaptic inhibitory activity of 2',3' and 5'-adenine nucleotides in rat vas deferens

Abstract

In the isolated rat vas deferens stimulated at 0.2 Hz, [14C]labelled 5'-AMP, 5'-ADP and 5'-ATP (10 microM) inhibited twitch responses, were broken down to [14C]adenosine in the medium and incorporated into [14C]adenine ribonucleotides in the tissue. Pretreatment of tissues with 6-(2-hydroxy-5-nitrobenzyl)-thioguanosine (NBTGR), a potent inhibitor of adenosine transport, potentiated the presynaptic inhibitory action of these 5' nucleotides and reduced their incorporation in [14C]adenine nucleotides, but did not alter the appearance of [14C]adenosine in the medium. A series of 2', 3' and 5'-substituted adenine nucleotides (10 microM) inhibited the twitch responses of the vas deferens stimulated at 0.2 Hz. This effect was potentiated by NBTGR. Addition of exogenous adenosine deaminase very significantly reduced the inhibitory actions of adenosine, 5'-AMP, 5'-ADP and 5'-ATP and also reduced those of 2', 5'-ADP, NAD+ and dePCoA. The inhibitory actions of the other 2', 3' and 5' adenine nucleotides studied were not altered by exogenous adenosine deaminase. These results indicated that the presynaptic inhibitory actions of 5'-AMP, 5'-ADP and 5'-ATP in rat vas deferens predominantly result from their prior hydrolysis to adenosine whereas the 2', 3' and 5'-substituted adenine nucleotides appear to act mainly directly to inhibit transmitter release.