Steep gradients in amino acid profiles between endolymph and perilymph

Using high performance liquid chromatography, we have determined 19 amino acids (AAs) in cochlear and utricular endolymph, cochlear and vestibular perilymph, and cerebrospinal fluid (CSF) of the guinea pig. Glutamate and aspartate are markedly higher in both cochlear and utricular endolymph than in perilymph, confirming our previous studies on cochlear endolymph based on enzymatic cycling [Thalmann et al., J. Acoust. Soc. Am. Suppl. 1 66, S47 (1979)]. The remaining AAs are significantly lower in both endolymphatic compartments, in most cases by an order of magnitude. Nevertheless, significant differences between the AA profiles of cochlear and utricular endolymph exist. AA concentrations of perilymph of scala vestibuli and vestibular cistern are higher than in CSF, in two cases by an order of magnitude. In scala tympani the AA composition is highly variable depending upon sampling method and surgical manipulation preceding sampling (relief of CSF pressure, obstruction of cochlear aqueduct). Without surgical interference, those AAs which are very low in CSF are considerably lower in scala tympani than in scala vestibuli, suggesting substantial natural or artifactual admixture of CSF. These same AAs increase in concentration when CSF pressure is relieved or the cochlear aqueduct blocked. [Supported by NIH grants NS14334 and NS06575.]