Water permeability of the endolymph-perilymph barrier in the guinea pig cochlea

Expression of aquaporins and vasopressin type 2 receptor in the stria vascularis of the cochlea

“…The present results suggest that the BC is the target organ of VP and that VP-AQP-2 mediated water transport occurs actively in the BC toward the endolymphatic system. Since the driving force of AQP water channels is the osmotic gradient and the osmolarity of the endolymph is significantly higher than that of the perilymph (Konishi et al, 1984;Sterkers et al, 1984), the water in the perilymphatic compartment might enter into the intracellular space of the BC via AQP-2 water channels, and then the water in the intracellular space of the BC might exit into the extracellular space of the SV (intrastrial space) via AQP-3.…”

Water permeability of the mammalian cochlea: functional features of an aquaporin-facilitated water shunt at the perilymph–endolymph barrier

“…The calculations of P D and P f in this study were based on previously derived in vivo experimental data on diffusional [44] and osmotic [78] water exchange between the perilymphatic and endolymphatic fluid compartments to respectively determine P D and P f for the entire CDE, its individual partitions including RM and OC as well as the epithelial subdomain in the cochlear apex comprised by the subpopulation of OSCs co-expressing AQP4 and AQP5.…”

The effect of systemic administration of desmopressin on cochlear function in guinea pigs

“…We now consider the theory of endolymph volume regulation. While endolymph is often reported to be around 10-40 mOsmol greater than perilymph or the surrounding tissues [17], this in itself does not imply that there is an osmotic gradient forcing water into the scala media. That is, the bulk flow of water movement between two compartments is determined by the Starling equation J V = L P (Dp -sÁDp), where Jv is the bulk flow of fluid, Lp is the water permeability of the compartment boundary, Dp is the hydrostatic gradient, Dp is the osmotic gradient of each solute, such as K + , Na + , and Cl -, and s is the reflection coefficient for each solute at each boundary.…”

“…That is, the bulk flow of water movement between two compartments is determined by the Starling equation J V = L P (Dp -sÁDp), where Jv is the bulk flow of fluid, Lp is the water permeability of the compartment boundary, Dp is the hydrostatic gradient, Dp is the osmotic gradient of each solute, such as K + , Na + , and Cl -, and s is the reflection coefficient for each solute at each boundary. Although it is thought that dDAVP treatment mainly changes Lp via changes in the expression of V2 receptors and AQP2 channels, it would be difficult to estimate the direction of bulk water flow without knowing the details of the reflection coefficients (s) of each boundary (although valiant efforts to determine these properties have been previously performed [17]). A difference in the reflection coefficient of solutes could easily result in a force that drives water out of one compartment into another compartment, even causing water to flow out of a compartment that is hypo-osmotic.…”