1978 Volume 24 Issue 5 Pages 819-825
Some types of the sudden deafness which shows the spontaneous recovery is a most typical one of the sensorineural deafness the hearing level of which shifts remarkedly. In this case, because of the presence of hearing recovery, the cause of deafness should be attributed to rather something else than the organic changes of the receptor organs, such as the degeneration of hair cells and the nerve fibers.
Depending on the present knowledge in the electrophysiological territory of the inner ear, the reduction or disappearance of EP, the origin of which must lie somewhere in the stria vascularis, seems to be the most conceivable factor to induce this type of deafness. This study was undertaken to determine whether or not such consideration is right.
In order to induce the reduction of DC potential gradient at the reticular layer, Furosemide which is a salturetic drug and is already wellknown to bring about the marked reduction of EP was used in this experiment.
Throughout the experiment, CM and EP were recorded by an ordinary glass-micro-electrode from the scala media of the basal turn of the cochlea in guinea pigs, while the K+ ion concentration in endolymph was measured simultanously by using a specific K+ ion sensitive microelectrode.
After the intravenous injection of furosemide, EP and CM declined rapidly. After reaching their lowest levels within 1 minute, EP and CM began to recover immediately. The recovery of CM was much more rapid than EP, and the remarkable over-shoot of the amplitude of CM was already observed even when the EP still stayed at a lower level of voltage. This experimental fact indicates that the high voltage of EP is not always needed to produce CM.
In order to clarify the cause of early recovery of CM which seemed to be inreasonable in relation to the magnitude of EP voltage, the K+ ion concentration in endolymph was observed after furosemide injection. Because it has been generally agreed that the high K+ ion concentration in endolymph must be most important chemical component for maintaining the CM sensitivity. The V ion concentration in endolymph did not alter at all at every stage of the reduction and recovery of EP and CM after furosemide injection. From this result, it can be concluded that the remarkable recovery of CM does not come from the sudden increase of K+ ion concentration in endolymph. For greater clarification about the inadequate relationship between the magnitude of CM and EP, which observed at the recovery stage after furosemide injection, it should be necessary to investigate not only the relation between V ion concentration in endolymph and cochlear potentials but also that between Na+ and Cl-ion concentration in endolymph and cochlear potentials.
