Effects of adenosine on action potentials in the oyster heart, with special reference to the activity of adenosine aminohydrolase

Adenosine deaminase in the adductor muscle of the scallop, Patinopecten yessoensis

1. The scallop enzyme was separated by DE52 ion-exchange chromatography into two forms with the same mol. wt of 38,000 and similar characteristics. 2. The enzyme was inactivated in the absence of dithiothreitol and complete reactivation was achieved by adding the agent within a critical storage period. 3. The apparent values of pKm and Vmax sensitively increased as ionic strength was raised to 250 mM and phosphate and sodium ions elevated the former value with a further increase of the ionic strength. 4. The apparent activation energies for the alpha (Vmax/Km) and beta (Vmax) parameters of both the forms were approximately 5 and 8 kcal/mol, respectively. 5. The enzyme deaminated 2'-, 3'-deoxyadenosine and 2',3'-isopropylidene adenosine but did not deaminate 5'-deoxyadenosine, alpha-adenosine and adenine nucleotides. 6. The affinity for inosine was much lowered with a high Ki value. Adenine and purine riboside inhibited the enzyme completely, and coformycin was a tight, slow binding inhibitor.

Purinergic modulation in the brain of the spiny lobster

Earlier studies identified purinergic chemoreceptors in the olfactory organ of the spiny lobster, Panulirus argus. In this study, electrophysiological experiments demonstrate that purinergic substances can modulate both the spontaneous activity and the evoked responses of neurons within the brain of this animal. Perfusion of the brain with 100 microM adenosine 5'-monophosphate (AMP) modulated the spontaneous activity of 71% of the brain interneurons that were monitored. AMP also modulated the electrically or chemically evoked activity of 25% of the monitored interneurons. The effects were dose-dependent (down to 1 microM) and reversible. The modulatory effects of adenosine were similar to those of AMP, and were antagonized by the adenosine receptor antagonist 1,3-dipropyl-8-p-sulfophenylxanthine. The modulation by AMP or adenosine was depressive in most but not all neurons, as is the case with purinergic effects in the brain of vertebrates. We believe this is the first demonstration of modulatory effects of purinergic substances in the nervous system of any invertebrate.