Two subtypes of G protein-coupled nucleotide receptors, P2Y1and P2Y2are involved in calcium signalling in glioma C6 cells

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Abstract
In glioma C6 cells, the stimulation of P2Y receptors by ADP, ATP and UTP initiated an increase in the intracellular Ca2+ concentration, in a process that involved the release of Ca2+ from InsP3‐sensitive store and the capacitative, extracellular Ca2+ entry. The presence of external Ca2+ was not necessary to elevate Ca2+. The rank order of potencies of nucleotide analogues in stimulating [Ca2+]i was: 2MeSADP > ADP > 2MeSATP = 2ClATP > ATP > UTP. α,β‐Methylene ATP, adenosine and AMP were ineffective. ADP and UTP effects were additive, while actions of ATP and UTP were not additive on [Ca2+]i increase. Similarly, cross‐desensitization between ATP and UTP but not between ADP and UTP occurred. Suramin, a non‐specific nucleotide receptors inhibitor, antagonized ATP‐, UTP‐ and ADP‐evoked Ca2+ responses. PPADS, a selective antagonist of the P2Y1 receptor‐generated InsP3 accumulation, decreased ADP‐initiated Ca2+ response with no effect on ATP and UTP. Pertussis toxin (PTX) reduced ADP‐ and ATP‐induced Ca2+ increases. Short‐term treatment with TPA, inhibited both ATP and ADP stimulatory effects on [Ca2+]i. ADP inhibited isoproterenol‐induced cyclic AMP accumulation. PTX blocked this effect, but PPADS did not. RT – PCR analysis revealed the molecular identity of P2Y receptors expressed by glioma C6 cells to be both P2Y1 and P2Y2. It is concluded that both P2Y1 and P2Y2 receptors co‐exist in glioma C6 cells. ADP acts as agonist of the first, and ATP and UTP of the second one. Both receptors are linked to phospholipase C (PLC). British Journal of Pharmacology (2001) 132, 393–402; doi:10.1038/sj.bjp.0703843