Effects of pertussis toxin on signal transductions via P2-purinergic receptors in A-431 human epidermoidal carcinoma cells.

In A-431 cells, stimulation of P2-purinergic receptors with extracellular ATP caused production of inositol 1,4,5-trisphosphate (InsP3), followed by mobilization of Ca2+ from intracellular stores; Ca2+ influx from the extracellular fluid and breakdown of phosphatidylcholine (PtdCho) also accompanied this InsP3/Ca2+ signalling. When A-431 cells were pretreated with pertussis toxin (PTX), production of InsP3 and elevation of cytosolic Ca2+ were strongly inhibited. PTX also inhibited the Ca2+ influx, but the effect was much weaker than that for InsP3/Ca2+ elevation. No inhibitory effect was observed in ATP-stimulated PtdCho breakdown. These results suggest that there is a system(s) which mediates the functions of P2-purinergic receptors in addition to PTX-sensitive G-proteins.