P2Y(1) and P2Y(12) receptor cross-talk in calcium signalling: Evidence from nonstarved and long-term serum-deprived glioma C6 cells.

The current work presents results of experiments on the calcium response evoked by the stimulation by extracellular nucleotides occurring in control, nonstarved glioma C6 cells and in cells after long-term (96 h) serum starvation. Three nucleotide receptors were studied: P2Y(1), P2Y(2) and P2Y(12). Two of them, P2Y(1) and P2Y(2), directly stimulate calcium response. The protein level of the P2Y(2) receptor did not change during the serum starvation, while P2Y(1) protein level fell dramatically. Observed changes in the calcium response generated by P2Y(1) are directly correlated with the receptor protein level as well as with the amount of calcium present in the intracellular calcium stores, partially depleted during starvation process. The third receptor, P2Y(12), did not directly evoke calcium response, however it is activated by the same ligand as P2Y(1). The experiments with AR-C69941MX, the P2Y(12)-specific antagonist, indicated that in control and serum-starved cells, calcium response evoked by P2Y(1) receptor is potentiated by the activity of P2Y(12)-dependent signaling pathways. This potentiation may be mediated by P2Y(12) inhibitory effect on the plasma membrane calcium pump. The calcium influx enhanced by the cooperation of P2Y(1) and P2Y(12) receptor activity directly depends on the capacitative calcium entrance mechanism.