Extracellular
nucleotides exert a variety of
biological actions through several kinds of P2 receptors in many tissues and cell types. We found that treatment with
nucleotides increases intracellular Ca2+ concentration ([Ca2+]i) in SK-N-BE(2)C human
neuroblastoma cells with a following order of potency:
UDP >
UTP >
ADP >>
ATP. Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that specific mRNAs coding for human P2Y1, P2Y4, and
P2Y6 receptors were expressed in the cells, but Northern blot analysis revealed that
P2Y6 receptors were the predominant type. Activation of
protein kinase C-alpha by treatment with 1 micro m
phorbol 12-myristate 13-acetate dramatically inhibited both the
UDP-induced [Ca2+]i rise and
inositol 1,4,5-trisphosphate (IP3) generation, whereas incubation with
pertussis toxin had little effect on the responses. The
UDP-induced [Ca2+]i rise and IP3 production were maintained up to 30 min after stimulation, while
bradykinin-induced responses rapidly decreased to the basal level within 5 min of stimulation. Pretreatment of cells with the maximal effective concentration of
UDP reduced the subsequent
carbachol- or
bradykinin-induced [Ca2+]i rise without inhibition of IP3 generation. Neuronal differentiation of the cells by treatment with
retinoic acid for 7 days did not change the expression level of
P2Y6 receptors. Taken together, the data indicate that
P2Y6 receptors highly responsive to diphosphonucleotide
UDP are endogenously expressed in the human
neuroblastoma SK-N-BE(2)C cells and that they are involved in the modulation of other
phospholipase C-coupled receptor-mediated Ca2+ mobilization by depleting the IP3-sensitive Ca2+ stores.