Disturbances in purinergic [Ca2+]i signalling pathways in a transformed rat thyroid cell line.

It was previously shown that in rat thyroid PC-C13 cell line, a purinergic P2Y receptor increases the concentration of free cytosolic Ca2+ ([Ca2+](i)) via phospholipase C activation. We here studied whether in a transformed cell line (PC-E1Araf) derived from parental PC-C13 cells, ATP is still able to transduce the [Ca2+](i)-based intracellular signal. We demonstrate the expression of mRNA for P2Y2 in both PC-C13 and PC-E1 Araf cells; mRNAs for P2Y1, P2Y4, P2Y6 and P2Y11 were absent. In both cell lines activation of P2Y2 receptor provokes a transient increase in [Ca2+](i) followed by a lower sustained phase persisting for over 5 min in PC-C13 and only 1.5 min in PC-E1Araf cells. In both cell lines the [Ca2+](i) reached a plateau level significantly higher than the basal [Ca2+](i) level persisting for over 10 min. Removal of extracellular Ca2+ reduced the initial transient response to ATP in PC-C13, but not in PC-E 1 Araf cells, and completely abolished the plateau phase in both cell lines. In the presence of extracellular Ca2+ thapsigargin (TG) caused a rise in [Ca2+](i) significantly higher in PC-C13 than transformed PC-E1 Araf cells, while in Ca2+-free medium the effect of TG was similar in both cell lines. The capacitative Ca2+-entry in PC-C13 resulted significantly higher than in PC-E I Araf cells. Further studies were performed in order to investigate whether the different effects of ATP on [Ca2+](i) was due to variation in divalent cation plasma membrane permeability. PC-E1Araf cells showed a much lower permeability to Ca2+, Ba2+, Sr2+, Mn2+, and Co2+ that may be responsible for the differences in purinergic Ca2+ signaling pathway with respect to parental PC-C13 cells