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

According to Davis' (1965) model of the inner ear, a potential difference b etween the endocochlear potential and the hair cell resting potential drive s the transduction current across the apical hair cell membrane. It is assu med that the endocochlear potential (EP) consists of two components. The fi rst is a diffusion potential, which depends on the ionic composition of end olymph and perilymph and on the permeability of the perilymph-endolymph bar rier. 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 resp onsible for the measured EP in birds. The present paper studies whether ion ic compositions of endo- and perilymph might explain the EP in birds. Conce ntrations 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 tympa ni and scala vestibuli). In scala media, the concentrations of K+, Ca2+ and Cl- were 140.6, 0.23 and 142.1 mM. (C) 1999 Elsevier Science B.V. All righ ts reserved.