P¹,P⁵-Di(adenosine-5′) pentaphosphate ammonium salt

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.