RESUMEN
ATP, as a paracrine signalling molecule, induces intracellular Ca2+ elevation via the activation of purinergic receptors on the surface of glia-like cochlear supporting cells. These cells, including the Deiters' cells (DCs), are also coupled by gap junctions that allow the propagation of intercellular Ca2+ waves via diffusion of Ca2+ mobilising second messenger IP3 between neighbouring cells. We have compared the ATP-evoked Ca2+ transients and the effect of two different gap junction (GJ) blockers (octanol and carbenoxolone, CBX) on the Ca2+ transients in DCs located in the apical and middle turns of the hemicochlea preparation of BALB/c mice (P14-19). Octanol had no effect on Ca2+ signalling, while CBX inhibited the ATP response, more prominently in the middle turn. Based on astrocyte models and using our experimental results, we successfully simulated the Ca2+ dynamics in DCs in different cochlear regions. The mathematical model reliably described the Ca2+ transients in the DCs and suggested that the tonotopical differences could originate from differences in purinoceptor and Ca2+ pump expressions and in IP3-Ca2+ release mechanisms. The cochlear turn-dependent effect of CBX might be the result of the differing connexin isoform composition of GJs along the tonotopic axis. The contribution of IP3-mediated Ca2+ signalling inhibition by CBX cannot be excluded.
