Regulation of extracellular ATP in the zebrafish retina: ectonucleotidases localization and activity

ALFIE, L.D., SCHWARZBAUM, P.J., FAILLACE, M.P.

Pinamar

Congreso; 20ava Reunion anual de l a Sociedad Argentina de Neuroquimica; 2005

ATP is released by neurons and acts as a neurotransmitter and neuromodulator via purinergic receptors. Extracellular ATP concentrations are precisely regulated by ecto-nucleoside-triphosphate diphosphohydrolases (ENTPDases). Resulting AMP is further metabolized extracellularly to adenosine, a potent inhibitory neuromodulator. We showed that two major subtypes of ectonucleotidases: ENTPDase 1 and 2 are expressed in the zebrafish retina both by western blot and immunohistochemistry on 10 µm tissue sections. Both enzymes are heterogeneously distributed among retinal layers, principally expressed in the inner half of the retina but their expression pattern overlaps only partially. ENTPDases 1 and 2 activities can be distinguished one from each other by autoradiography using radioactive nucleotides as substrates. To date, we demonstrated extracellular ATPase activity on zebrafish retinal sections by this methodology. We are currently comparing whether the site of ATP hydrolysis matches the immunoreactivity patterns for both enzymes. In conclusion, the retina of zebrafish contains two different ENTPDases with ATPase activity. Interestingly, these enzymes show a specific distribution on cell subtypes and synaptic retinal layers. Since ENTPDase 1 produces AMP in a much higher rate than ENTPDase 2, our results suggest a localized regulation of extracellular adenosine levels.