Mitochondria modulate the spatio-temporal properties of intra- and intercellular Ca signals in cochlear supporting cells

In the cochlea, cell damage triggers intercellular Ca²⁺ waves that propagate through the glial-like supporting cells that surround receptor hair cells. These Ca²⁺ waves are thought to convey information about sensory hair cell-damage to the surrounding supporting cells within the cochlear epithelium. Mitochondria are key regulators of cytoplasmic Ca²⁺ concentration ([Ca²⁺]_cyt), and yet little is known about their role during the propagation of such intercellular Ca²⁺ signalling. Using neonatal rat cochlear explants and fluorescence imaging techniques, we explore how mitochondria modulate supporting cell [Ca²⁺]_cyt signals that are triggered by ATP or by hair cell damage. ATP application (0.1–50 μM) caused a dose dependent increase in [Ca²⁺]_cyt which was accompanied by an increase in mitochondrial calcium. Blocking mitochondrial Ca²⁺ uptake by dissipating the mitochondrial membrane potential using CCCP and oligomycin or using Ru360, an inhibitor of the mitochondrial Ca²⁺ uniporter, enhanced the peak amplitude and duration of ATP-induced [Ca²⁺]_cyt transients. In the presence of Ru360, the mean propagation velocity, amplitude and extent of spread of damage-induced intercellular Ca²⁺ waves was significantly increased. Thus, mitochondria function as spatial Ca²⁺ buffers during agonist-evoked [Ca²⁺]_cyt signalling in cochlear supporting cells and play a significant role in regulating the spatio-temporal properties of intercellular Ca²⁺ waves.