P-2 PURINERGIC RECEPTORS FOR DIADENOSINE POLYPHOSPHATES IN THE NERVOUS-SYSTEM

1. The actions of diadenosine polyphosphates, diadenosine tetraphospha te (Ap(4)A), diadenosine pentaphosphate (Ap(5)A) and diadenosine hexap hosphate (Ap(6)A) in the nervous system have been reviewed. 2. In the peripheral nervous system, diadenosine polyphosphates bind to P-2-puri nergic receptors such as the P-2Y in chromaffin cells and Torpedo syna ptosomes, P-2X in vas deferens and urinary bladder and also Torpedo sy naptosomes and P-2U in endothelial chromaffin cells. 3. In the central nervous system Ap(n)A compounds can act through P-2X-purinoceptors op ening cation channels in nodose ganglion neurones, Diadenosine polypho sphates bind to a P-2d-purinergic receptor in rat brain synaptic termi nals and hippocampus, linked to protein kinase C (PKC) activation. 4. P-4-purinoceptors are specific receptors for diadenosine polyphosphate s, coupled to the Ca2+ influx, in the central synapses. This purinocep tor is not activated by ATP and synthetic analogs. The P-4-purinocepto r could act as a positive modulator of the synaptic transmission, givi ng even more importance to diadenosine polyphosphates as neurotransmit ters.