Intercellular Ca2+ Signalling In The Adult Mouse Cochlea

We have investigated wave-like cytoplasmic calcium (Ca2+) signalling in an ex vivo preparation of the adult mouse organ of Corti. Two types of intercellular Ca2+ waves that differ in propagation distance and speed were observed. One type was observed to travel up to 100 mu m with an average velocity of 7 mu m/s. Such waves were initiated by local tissue damage in the outer hair cell region. The propagation distance was decreased when the purinergic receptor antagonists pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS; 50 mu m) or suramin (150 mu m) were added to the extracellular buffer. Immunocytochemical analysis and experiments with calcium indicator dyes showed that both P2X and P2Y receptors were present in supporting cells. A second class of waves identified to travel longitudinally along the organ of Corti propagated at a lower velocity of 1-3 mu m/s. These 'slow' Ca2+ waves were particularly evident in the inner sulcus and Deiters' cells. They travelled for distances of up to 500 mu m. The slow Ca2+ signalling varied periodically (approximately one wave every 10 min) and was maintained for more than 3 h. The slow waves were not affected by apyrase, or by the P2 receptor agonists suramin (150 mu m) or PPADS (50 mu m) but were blocked by the connexin channel blockers octanol (1 mm) and carbenoxolone (100 mu m). It is proposed that the observed Ca2+ waves might be a physiological response to a change in extracellular environment and may be involved in critical gene regulation activities in the supporting cells of the cochlea.