An analysis of the adenosine receptors responsible for modulation of an excitatory acetylcholine response on an identified Helix neuron.
1. Electrophysiological recordings were made from an identified neuron, F1, in the isolated suboesophageal ganglionic mass of Helix aspersa. 2. Bath applied adenosine (AD) (60-600 nM) depressed the depolarisation induced in the cell F1 by bath or iontophoretically applied acetylcholine (ACh). L-Phenylisopropyladenosine (L-PIA) also depressed the ACh response but NECA had no depressive effect. This effect of AD or L-PIA is inhibited by 12 microM 8-phenyltheophylline and is believed to be mediated by an A1 receptor. 3. If the proportion of the excitatory ACh response that was carried by calcium ions was increased, the percentage depression of this modified response by AD was significantly greater. 4. There was a residual current evoked by ACh in high calcium/sodium free Ringer. This ACh induced current was antagonized by 3 mM cobalt or 50 microM verapamil suggesting that it was calcium mediated. This residual current was also completely abolished by 0.6 microM AD. 5. Lower bath concentrations of AD (0.6-6 nM) and L-PIA than caused the depression of the ACh response and also adenosine triphosphate (ATP) (0.7 microM) and alpha,beta-methylene ATP (0.6 microM), enhanced the ACh D response. The relative potencies of AD and its two analogues 5'-N-ethylcarboxamideadenosine (NECA) and L-PIA in causing this enhancement of the ACh response were: NECA greater than AD greater than L-PIA. This is the potency ranking described for an A2 receptor.
D000109:Acetylcholine / Q000494:pharmacology*; D000241:Adenosine / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D006372:Helix, Snails; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D011983:Receptors, Purinergic / Q000187:drug effects / Q000502:physiology*
D011983:Receptors, Purinergic; D000241:Adenosine; D000109:Acetylcholine; D002118:Calcium