AQP5 and endolymphatic hydrops: However, according to the findings of Hirt and coworkers [12], there should be further attention paid to the special differential localization and role of AQP5 and AQP 4 in the outer sulcus cells, as it suggests a possible water shunt in the perilymph—endolymph barrier which could have an impact on dysfunctional water regulation such as endolymphatic hydrops or sensorinureal hearing loss.