Sodium, potassium, chloride and calcium concentrations measured in pigeon perilymph and endolymph

According to Davis' (1965) model of the inner ear, a potential difference between the endocochlear potential and the hair cell resting potential drives the transduction current across the apical hair cell membrane. It is assumed that the endocochlear potential (EP) consists of two components. The first is a diffusion potential, which depends on the ionic composition of endolymph and perilymph and on the permeability of the perilymph-endolymph barrier. The second is an electrogenic component which is determined by active ion transport across the perilymph-endolymph barrier. In birds, the EP is between +8 and +20 mV. Little is known about the underlying mechanisms responsible for the measured EP in birds. The present paper studies whether ionic compositions of endo- and perilymph might explain the EP in birds. Concentrations of Na+, K+, Ca2+ and Cl- in pigeon scala vestibuli, scala tympani and scala media were determined with ion-selective microelectrodes. Na+, K+, Ca2+ and Cl- were 150.0, 4.2, 1.4 and 117.0 mM in perilymph (scala tympani and scala vestibuli). In scala media, the concentrations of K+, Ca2+ and Cl- were 140.6, 0.23 and 142.1 mM.