Ectonucleotidases in the nervous system.

Extracellular nucleotides are hydrolysed by enzymes of the plasma membrane with an extracellularly oriented catalytic site (ectonucleotidases). Members of several families of ectonucleotidases can contribute to extracellular nucleotide hydrolysis. They have been characterized in molecular and functional terms. A major role of these enzymes is in the modulation of ligand availability at nucleotide and nucleoside receptors. The enzymes reveal a wide and partially overlapping tissue distribution. The diversity of the individual family members is considerable and it is still difficult to assign identified enzymes to the modulation of purinergic signalling pathways. In the brain, members of all ectonucleotidase-families are expressed. Proposed physiological functions include modulation of synaptic transmission, of the ATP-mediated propagation of glial Ca2+ waves, of microglial function, adult neurogenesis or the control of vascular tone, haemostasis and thromboregulation.