Cochlear transduction is examined by characterizing electrical and ionic gradients in the cochlea in silence and during acoustic stimulation. The gradients are associated with a current, generated by the stria vascularis, that flows through the sensory receptor cells found in the organ of Corti. The current completes a closed local circuit by flowing radially in scala tympani, entering the spiral ligament and returning to the stria vascularis, where it is driven by a metabolical active pump back into scala media. The experiments are based on an analysis of cochlear physiology that considers the paths followed by intracochlear currents and attempts to integrate the function of the structures through which they pass. Clarification of the mechanisms by which the outer hair cells influence the inner hair cells is a major goal of the research. A new technique is used that involves recording potentials at fixed intervals along a microelectrode track and computing current density by calculating the first spatial derivative of the potential field. In some experiments potassium concentration gradients are measured simultaneously with potential gradients by using double barreled electrodes, one barrel of which has been made ion sensitive. The resulting two dimensional analysis of current density and potassium gradients in scala tympani and scala media provide a quantitative description of the current pathways through the hair cells and about the tectorial membrane. The effects of anoxia, ouabain and other drugs on the electrical and chemical gradients explore their strial origin as well as their pathways through the organ of Corti. Crossed olivocochlear bundle fibers terminate predominately on the outer hair cells so that changes in the electro-chemical gradients resulting from their stimulation can be attributed to the outer hair cell population. Other studies in the same laboratory have demonstrated that isolated outer hair cells change their length in response to electrical stimulation. Quantification of the intracochlear electric field is useful in assessing the possible role of these electrically evoked shape changes in vivo. The potassium ion measures provide information about the role of the stria vascularis and corroborate electric field measures. The electrical role of the outer hair cells in cochlear transduction will be clarified and important information will be provided on the physiology of the organ of Corti and the stria vascularis under normal and pathological conditions.
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