The P2Y GPCRs serve as receptors for extracellular nucleotides. P2Y is a relatively low affinity receptor for ATP present humans but not rodents. It is unique among P2Y receptors in increasing both cAMP and calcium levels. P2Y is expressed in immune cells, and it mediates dendritic cell maturation induced by ATP. In addition to ATP, NAD+ and NADP+ bind and activate P2Y in granulocytes. An alternate form of P2Y, in which the second exon of P2Y1 undergoes intergenic splicing with exon 12 of the adjacent SSF1 gene to generate a chimeric protein, is widely expressed in human tissues.