Novel structurally altered P2X1 receptor is preferentially activated by adenosine diphosphate in platelets and megakaryocytic cells

Experimental and clinical data suggest the presence of multiple types of adenosine diphosphate (ADP) receptors, one coupled to ligand-gated cation channels (P2X) and others coupled to G-protein–coupled (P2Y) receptors. This report identifies cDNA for a structurally altered P2X1-like receptor in megakaryocytic cell lines (Dami and CMK 11-5) and platelets that, when transfected into nonresponsive 1321 cells, confers a specific sensitivity to ADP with the pharmacologic rank order of ADP > > ATP > > > α,β-methylene-ATP as measured by Ca++ influx. This receptor (P2X1del) contains a deletion of 17 amino acids (PALLREAENFTLFIKNS) that includes an NFT consensus sequence for N-linked glycosylation. Glycosylated forms of the P2X1deland P2X1wt receptors were indistinguishable electrophoretically by Western blot or by immunoprecipitation using available antihuman and antirat antibodies. These results indicate that the expression of the P2X1del receptor results in an influx of Ca++ induced by ADP. Expression of P2X1delreceptor homomeric subunits is sufficient to express a receptor preferentially activated by ADP and suggests that this altered form, alone or in combination with P2X1wt receptors, is a component of an ADP-activated ion channel.