Diadenosine polyphosphates, extracellular function and catabolism

Abstract

Diadenosine polyphosphates (ApnA n = 2-6) are natural compounds that play an important role inside the cell, in both the nucleus and at the cytosol. The transport of ApnA to cytoplasmatic storage granules provides both the end of their intracellular actions and at the same time the way to be released by controlled exocytosis. Diadenosine polyphosphates are co-stored and co-released from a large variety of synaptic terminals. Their physiological extracellular concentration range can be expected to be between the nM and low μM. Binding studies have detected the presence of high affinity sites, correlating with the physiological concentrations . From a functional point of view, specific receptors, called “dinucleotide receptors” or “P4 receptors,” have been described in presynaptic terminals and elicit calcium entrance through ionotropic receptors that are not susceptible to inhibition by voltage dependent calcium channel toxins. The extracellular actions of diadenosine polyphosphates are terminated by the enzymatic hydrolysis by an ecto-diadenosine polyphosphate hydrolase.