ATP and ADP Hydrolysis in Fish, Chicken and Rat Synaptosomes

Ecto-enzymes capable of hydrolyzing ATP and ADP (NTPDase) are present in the central nervous system of various species. In the present investigation we studied the synaptosomal NTPDase (ATP diphosphohydrolase, apyrase, E.C. 3.6.1.5) from fish, chicken and rats under different conditions and in the presence of several classical inhibitors. The cation concentration required for maximal activity was 0.5 mM for fish, 1.0 mM for chickens and 1.5 mM for rats with both substrates. The results showed that the pH optimum for all animal preparations was close to 8.0. The temperature used was 25-27 degrees C for fish and 35-37 degrees C for chicken and rat preparations. The inhibitors azide and fluoride only inhibited the preparation at high concentrations (10 mM). Lanthanum (0.1-0.4 mM), N-ethylmaleimide (0.4-3.0 mM) and ouabain (0.5-3.0 mM) had no effect on NTPDase activity from fish, chickens or rats. Orthovanadate (0.1-0.3 mM) only inhibited fish synaptosomal NTPDase. Trifluoperazine (0.05-0.2 mM) and suramin (0.03-0.3 mM) inhibited NTPDase at all concentrations tested. Suramin was the most potent compound in causing inhibition, presenting inhibition at 30 microM. Our results demonstrate that the synaptosomal NTPDase response to several factors is similar in fish, chickens and rats, and that the enzyme presents functional homology.