On the specificity and type of receptor involved in carotid body chemoreceptor activation by adenosine in the cat.

Experiments were performed on cats anaesthetized with pentobarbitone in which carotid chemoreceptor activity was recorded from the peripheral end of a sectioned carotid sinus nerve. Intracarotid injections of adenosine 5'-triphosphate (ATP) (1-100 micrograms i.c.) caused a dose-related increase in chemosensory discharge which was delayed in onset. The adenosine uptake inhibitor dipyridamole potentiated the chemoexcitatory effects of injected adenosine and ATP. The stable ATP analogue alpha-beta-methylene ATP (10-100 micrograms i.c.) depressed chemoreceptor discharge, which suggests the presence of a P2-purinoceptor in the carotid body, and provides evidence that the chemoexcitatory effect of ATP results from its hydrolysis to adenosine 5'-phosphate (AMP)/adenosine. Adenine, inosine, guanosine, cytidine and uridine had no appreciable effect on chemoreceptor discharge. The adenosine R-site agonists 2'-chloroadenosine and N6-methyladenosine had chemoexcitatory effects which were similar to those of adenosine, whereas the P-site agonist 2'-deoxyadenosine had no appreciable effect on discharge. We conclude that the adenosine receptor in the cat carotid body has some of the characteristics of an R-site receptor according to the classification of Londos & Wolff (1977).