Alec N. Salt
John E. DeMott
Dept. of Otolaryngol., Washington Univ. School of Medicine, 517 S. Euclid Ave., St. Louis, MO 63110
Longitudinal movements of endolymph were quantified in vivo in the basal turn of the guinea pig cochlea during injections of artificial endolymph into the second turn at rates up to 70 nl/min. Flow measurements utilized the marker ion tertramethylammonium (TMA), which was iontophoretically injected into the basal turn. TMA dispersion was measured by two ion-selective microelectrodes, one placed 0.5 mm apical, and the other 0.5 mm basal to the TMA injection site. Longitudinal endolymph movements were calculated from the recorded TMA time courses. Prior to injections, endolymph flow rates were extremely low. Volume injection into the second turn induced basally directed flows in the basal turn. The relationship between the measured rate and the injection rate was nonlinear, in which low-injection rates produced proportionately less flow than higher rates. These data show that for injections at low rates, volume disturbances have primarily local effects, presumably generating local distension or being compensated by local homeostatic mechanisms. At higher rates, basally directed endolymph flow becomes increasingly significant. These findings suggest that two independent processes may be involved in the regulation of endolymph volume. [Work supported by NIH Grant No. DC01368.]