Characterization of the purinergic P2 receptors in PC12 cells. Evidence for a novel subtype.

The properties of the purinergic receptors in the PC12 cells were studied. The rank order of potency to increase [Ca2+]i was: adenosine 5'-O-(1-thiotriphosphate) > ATP > adenosine 5'-O-(3-thiotriphosphate) >>> 3'-O-(4-benzoyl-benzoyl)ATP. ADP, AMP, GTP, UTP, alpha, beta- and beta,gamma-methylene adenosine 5'-triphosphates, 5'-adenylylimido-diphosphate, and adenosine analogues were ineffective. Although tetrabasic ATP4- was the form responsible for activation of the P2 receptors, ATP4- did not cause cell membrane permeabilization. The binding of alpha-35S-ATP to the intact cells showed a divalent cation dependency and a binding profile similar to the rank order of potency to increase [Ca2+]i. Scatchard plots of the equilibrium saturation binding data were nonlinear, and dissociation kinetics of the radioligand were best described using two kinetic rates. Different kinetic rates were, however, obtained when dissociation was initiated by the addition of excess ATP or by an 80-fold dilution. The present study describes a purinergic P2 receptor on PC12 cells that does not fit the classification for the P2x, P2y, P2t, P2u, and P2z receptor subtypes.