The sarcoplasmic-endoplasmic reticulum Ca2+ ATPase 2b regulates the Ca2+ transients elicited by P2Y2 activation in PC Cl3 thyroid cells

In PC C13 cells, a continuous, fully differentiated rat thyroid cell line, P2Y(2) purinoceptor activation provoked a transient increase of [Ca2+](i), followed by a decreasing sustained phase. The alpha and beta 1 protein kinase C (PKC) inhibitor Go 6976 decreased the rate of decrement to the basal [Ca2+](i) level and increased the peak of Ca2+ entry of the P2Y(2)-provoked Ca2+ transients. These effects of Go 6976 were not caused by an increased permeability of the plasma membrane, since the Mn2+ and Ba2+ uptake were not changed by Go 6976. Similarly, the Na+/Ca2+ exchanger was not implicated, since the rate of decrement to the basal [Ca2+](i) level was equally decreased in physiological and Na+-free buffers, in the presence of Go 6976. On the contrary, the activity of the sarcoplasmic-endoplasmic reticulum Ca2+ ATPase (SERCA) 2b was profoundly affected by Go 6976 since the drug was able to completely inhibit the stimulation of the SERCA 2b activity elicited by P2-purinergic agoinsts. Finally, the PKC activator phorbol myristate acetate had effects opposite to Go 6976, in that it markedly increased the rate of decrement to the basal [Ca2+](i) level after P2Y, stimulation and also increased the activity of SERCA 2b. These results suggest that SERCA 2b plays a role in regulating the sustained phase of Ca2+ transients caused by P2Y, stimulation