Figure 12. Ca²⁺ signalling in PDEC.

Agonist (UTP or ATP) concentration is ‘encoded’ as Ca²⁺ oscillation, sustained Ca²⁺ rise, or both via P2Y receptors in PDEC. The oscillatory signal is ‘decoded’ by a parallel activation of Ca²⁺-dependent K⁺ or Cl⁻ channels, whereas the sustained Ca²⁺ signal is decoded by both the Ca²⁺-activated channels and the exocytotic machinery. Finally, the Ca²⁺-activated channels modulate the Cl⁻-dependent HCO₃⁻ secretion while the Ca²⁺-activated exocytotic machinery promotes the exocytosis of secretory vesicles. For clarity, this diagram does not include additional modulatory effects of cAMP signals generated by P2Y receptors on exocytosis and channels that were demonstrated in our previous studies (Nguyen et al. 2001; Jung et al. 2004).