Extracellular ATP and P2Y2 receptors mediate intercellular Ca2+ waves induced by mechanical stimulation in submandibular gland cells: Role of mitochondrial regulation of store operated Ca2+ entry

Coordination of Ca2+ signaling among cells contributes to synchronization of salivary gland cell function. However, mechanisms that underlie this signaling remain elusive. Here, intercellular Ca2+ waves (ICW) in submandibular gland cells were investigated using Fura-2 fluorescence imaging. Mechanical stimulation of single cells induced ICW propagation from the stimulated cells through ∼7 layers of cells or ∼120 μm. Our findings indicate that an extracellular ATP-dependent pathway is involved because the purinergic receptor antagonist suramin and the ATP hydrolyzing enzyme apyrase blocked ICW propagation. However, the gap junction uncoupler oleamide had no effect. ATP is released from mechanically stimulated cells possibly through opening of mechanosensitive maxi-anion channels, and does not appear to be directly linked to cytosolic Ca2+. The ICW is propagated by diffusing ATP, which activates purinergic receptors in neighboring cells. This purinergic signaling induces a Ca2+ transient that is dependent on Ca2+ release via IP3 receptors in the ER and store operated Ca2+ entry (SOCE). Finally, inhibition of mitochondrial Ca2+ uptake modified ICW indicating an important role of these organelles in this phenomenon. These studies increase our understanding of purinergic receptor signaling in salivary gland cells, and its role as a coordination mechanism of Ca2+ signals induced by mechanical stimulation.