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Diadenosine pentaphosphate pentaammonium is an endogenous vasoactive purine dinucleotide which has been isolated from thrombocytes. Diadenosine polyphosphates (ApnA, n=2–7) have been identified as constituents of secretory vesicles such as in platelets, chromaffin cells, Torpedo synaptic terminals and brain synaptosomes[1][2].

A diadenosine polyphosphate stored in secretory granules of thrombocytes, chromaffin and neuronal cells. After release into the extracellular space, it affects a variety of biological activities in a wide range of target tissues. In the nervous system it acts through various purinergic receptors. It also activates 5′-nucleotidase and inhibits adenosine kinase activity in vitro. Ap5A is metabolized by soluble enzymes in the blood plasma and by membrane-bound ectoenzymes of a number of cell types including endothelial and smooth muscle cells. In heart, it increases contractile force and action potential duration, and shows an anti-β-adrenergic effect.

Human Endogenous Metabolite

[1] L Giraldez, et al. Adenosine triphosphate and diadenosine pentaphosphate induce [Ca(2+)](i) increase in rat basal ganglia aminergic terminals. J Neurosci Res. 2001 Apr 15;64(2):174-82. DOI:10.1002/jnr.1063
[2] Jesús Pintor, et al. Presence of diadenosine polyphosphates in human tears. Pflugers Arch. 2002 Jan;443(3):432-6. DOI:10.1007/s004240100696