The potassium concentration in the cochlear fluids of the embryonic and post-hatching chick

The potassium concentration was measured in the perilymphatic and endolymphatic spaces of the chick's cochlea using ion-specific microelectrodes. The mean values in post-hatching chicks were 8.1 and 161 mM/l, respectively and are thus the same as in mammals. The high potassium concentration is reached at the latest at stage E42, and thus before the tegmentum vasculosum is fully developed. The endocochlear potential of chicks was maximally +13 mV and thus somewhat below the published values for birds. Positive potentials in the endolymphatic space of 5 mV or more were already present in animals of age E41 and E42 and the developmental process is complete at the latest one day after hatching.