ATP and adenosine trigger the interaction of plasma membrane IP3 receptors with protein kinase A in oviductal ciliated cells

We have demonstrated that adenosine did not produce any change of intracellular free Ca²⁺ concentration (Ca²⁺]i) in oviductal ciliated cells; however, it increased the ATP-induced Ca²⁺ influx through the activation of protein kinase A (PKA). Uncaging of IP₃ and cAMP triggered a larger Ca²⁺ influx than did IP₃ alone. Furthermore, the IP₃ effect was abolished by Xestospongin C, an IP₃ receptor blocker. Whole-cell recordings demonstrated the presence of an ATP-induced Ca²⁺ current, and the addition of adenosine increased the peak of this current. This effect was not observed in the presence of H-89, a PKA inhibitor. Using excised macro-patches of plasma membrane, IP₃ generated a current, which was higher in the presence of the catalytic PKA subunit and this current was blocked by Xestospongin C. We show here that activation of plasma membrane IP₃ receptors directly triggers Ca²⁺ influx in response to ATP and that these receptors are modulated by adenosine-activated PKA.