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 ∼120μm. 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.