Teruzo Konishi

Effect of Anoxia on Cochlear Potentials

The anterior inferior cerebellar artery of guinea pigs was occluded, thereby interrupting the blood supply to the cochlea. Durations of occlusion ranged from 1 through 60 min. Cochlear microphonics, summating potential, action potential, and endocochlear potential were recorded before, during, and subsequent to occlusion. The differential effect of anoxia on the various potentials was observed, as well as the appearance of the large negative dc potential in scala media as anoxia progressed. For the brief occlusion durations, the amplitudes of all potentials except cochlear microphonics became greater than normal soon after the blood supply returned. Even for the longer anoxic intervals, the summating potential and the endocochlear potential exhibited super‐normality during the recovery process.

Ion Transport in Guinea Pig Cochlea:I. Potassium and Sodium Transport

The scala vestibuli and/or tympani in anesthetized guinea pigs was perfused with artificial perilymph containing 42K and 22Na for periods ranging from 5 to 60 minutes. Sound-evoked responses were recorded during the perfusion. The activities of 42K and 22Na in perilymph and endolymph were determined with a germanium detector in conjunction with a multichannel analyser. The perfusion of scala vestibuli and/or tympani did not result in appreciable changes in electrical responses. The introduction of 42K and 22Na into the scala tympani resulted in the rapid appearance of these radioisotopes in perilymph of the scala vestibuli. The activities of 42K and 22Na in perilymph of the scala tympani remained low with perfusion of scala vestibuli. This is in agreement with our Findings that the clearance of these radioisotopes was faster in scala tympani than in scala vestibuli. Our results further indicate that the endolymph took up 42K and extruded 22Na against the concentration gradients. The transport of 42K and 2...

Effects of exposure to noise on ion movement in guinea pig cochlea

Healthy guinea pigs were exposed to broad band noise at levels between 95 and 115 dBA for 7 days. A significant decrease of the sound-induced cochlear responses, together with a substantial increase of the endocochlear potential, was observed in guinea pigs exposed to noise at 105 or 115 dBA. Microsamples of the endolymph obtained from these guinea pigs showed a significant increase of K+ and Cl- concentrations and a decrease of Na+ concentration, when compared with those from control animals. The K+, Na+ and Cl- concentrations in the perilymph were not markedly affected by noise exposure. When the perilymphatic space was perfused with artificial perilymph containing 43K, 22Na or 36 Cl, the uptake of radiotracers into the endolymph showed a single exponential function of the perfusion time. When compared with rate constants in normal animals, the value of rate constant for K+ was significantly decreased in animals exposed to noise. These results indicate that ionic permeability changes of the endolymph-perilymph barrier are a significant factor in the physiological mechanisms underlying noise-induced hearing loss.

Effect of Calcium Deficiency on Cochlear Potentials

The scala vestibuli and/or scala tympani in guinea pigs were perfused with Na+ free Lockes solution, in which NaCl was replaced with either choline chloride or sucrose. Cochlear microphonics (CM), summating potential (SP), action potential (AP), and endocochlear potential (EP) were recorded from the basal turn before, during, and subsequent to, the perfusion. Complete replacement of the perilymph with Na+‐free solution did not alter EP and CM immediately, although AP was abolished rapidly. Lack of Na in the perilymph of scala tympani depressed AP more markedly than did a comparable deficiency in scala vestibuli. In most cases, the depression of AP was reversible and EP and CM showed a gradual decline after the perfusion. These data were further confirmed by the fact that tetrodotoxin at a concentration of 50λ/l did not modify EP and CM, although AP was abolished promptly. The mechanism underlying the generation of the receptor potential is discussed. [Work supported by National Institutes of Health, Publ...

Permeability to potassium of the endolymph-perilymph barrier and its possible relation to hair cell function

SummaryThe endocochlear potential and potassium concentrations in endolymph and perilymph were simultaneously measured in the basal turn of the guinea pig cochlea with double-barreled K+ selective electrodes. The K+ conductance and K+ permeability coefficient of the endolymph-perilymph barrier were calculated from the rate of change of endolymph K+ concentration relative to the K+ electrochemical potential difference recorded during permanent anoxia. When anoxia was induced in guinea pigs treated with kanamycin, the rate of decline of the electrochemical potential difference for K+ between the endolymph and perilymph was reduced when compared to normal guinea pigs. In guinea pigs exposed to broad band noise at 115 dBA for periods from 11–15 days, the rate of decline of the electrochemical potential difference for K+ across the endolymph-perilymph barrier was reduced but not to the extent found in guinea pigs treated with kanamycin. The K+ conductance and K+ permeability coefficient of the endolymph-perilymph barrier showed substantial decreases in noise exposed and kanamycin treated guinea pigs, as compared to normal guinea pigs. The magnitude of decrease of K+ permeability of the endolymph-perilymph barrier by noise or kanamycin was correlated with suppression of the maximum output of the cochlear microphonic.

Effects of the Electrical Stimulation of the Crossed Olivocochlear Bundle on Cochlear Potentials Recorded with Intracochlear Electrodes in Guinea Pigs

The effect of electrical stimulation of the crossed olivocochlear bundle (COCB) on cochlear potentials was studied in anesthetized and immobilized guinea pigs. Sound‐evoked responses and the endocochlear potential were measured simultaneously in the basal turn. The time course and the magnitude of the slow negative potential in the scala media produced by COCB stimulation can be modified by parameters of COCB stimuli. Augmentation of cochlear microphonic and inhibition of whole‐nerve action potential were found to be dependent on the slow negative potential in scala media and on parameters of the acoustic stimulus. The summating potential showed increase of the positivity with COCB stimulation. The role of the positive summating potential on the inhibition of action potential was discussed.

Some Observations on Negative Endocochlear Potential During Anoxia

The effects of anoxia on the endocochlear potential (EP) and +K and +Na concentrations in the endolymph were studied in three groups of guinea pigs: kanamycin-treated guinea pigs, waltzing guinea pigs and normal guinea pigs. The magnitude of the EP in kanamycin-treated guinea pigs and waltzing guinea pigs did not show marked deviation from that observed in normal animals. The +K and +Na concentrations in the endolymph in those animals with severe suppression of sound-evoked cochlear potentials were also within the normal range. The changes in +K and +Na concentrations in the endolymph in anoxic condition were similar in the three groups of animals. However, the rate of decline of the EP was slower in kanamycin-treated guinea pigs and old waltzing guinea pigs. In young waltzing guinea pigs showing moderate suppression on the cochlear microphonics, the decline of the EP during anoxia was comparable to that observed in normal guinea pigs. The results indicate that anoxia decreases +K and increases +Na concentrations in the endolymph in a similar fashion in kanamycin-treated guinea pigs, waltzing guinea pigs and normal guinea pigs. It is suggested that the decline of the EP during anoxia is correlated with the +K conductance of the organ of Corti.

Effects of noise on cochlear potentials and endolymph potassium concentration recorded with potassium-selective electrodes

Guinea pig cochleas were exposed to either broad-band noise at intensities between 95 and 115 dBA or octave-band noise centered at 380 Hz or 4.2 kHz at intensities between 115 and 125 dB SPL. Cochlear microphonics (CM), summating potentials (SP) and action potentials (AP) were recorded from differential electrodes in the perilymphatic scalae between successive 20-min periods of noise exposure. The endocochlear potential (EP) and endolymph potassium concentration [Kendo+] were recorded continuously from scala media using double-barreled potassium-sensitive electrodes. It was found that the initial exposure to noise at 115 dBA produced considerable suppression of the CM and AP, while the EP and [Kendo+] were elevated above their normal values. When animals previously treated with kanamycin were subjected to the same level of noise exposure no systematic increase in either EP ro [Kendo+] was observed. After prolonged exposure to 380 Hz octave-band noise at 125 dB SPL, a slow decline of EP and [Kendo+] was observed. The relationships between the changes in EP, [Kendo+] and CM are discussed.

Ion Transport in the Cochlea of Guinea Pig:II. Chloride Transport

The -Cl transport of endolymph--perilymph barrier in guinea pigs was studied by perfusing the perilymphatic space with artificial perilymph containing 36Cl and measuring the uptake of 36Cl in the endolymph. In normal animals no marked difference in -Cl concentration was found between the endodlymph and perilymph. The data showed that the uptake of 36Cl in the endodlymph could be represented by a simple exponential function of the perfusion time, the rate constant being 0.01 min-1. The concentration of 36Cl in the endolymph was greater with perfusion of the scala vestibuli than with perfusion of the scala tympani, indicating the Reissners membrane is more permeable to -Cl than the rest of the endolymph-perilymph barrier. Anoxia and local application of ouabain decreased the -Cl concentration and 36Cl uptake in the endolymph. Our results imply that the endocochlear potential is the principal driving force for unidirectional flux of -Cl from perilymph to endolymph.

Electrophysiological Studies on the Spatial Distribution of the Crossed Olivocochlear Bundle along the Guinea Pig Cochlea

The effectiveness of electrical stimulation of the crossed olivocochlear bundle (COCB) was measured at different locations along the cochlear partition. Differential electrodes were used to sample the cochlear microphonic (CM) at turns I, II, and III. A pipette inserted into scala media in turns I, II, and III was used to measure the slow negative potential associated with electrical stimulation of the COCB. The responses of auditory nerve fibers were sampled within the modiolus and included a wide range of best frequencies. The magnitude of the slow negative potential was maximum in turn I and decreased in turns II and III. The increment in CM, produced by COCB stimulation, depended not only upon the location along the cochlear partition from which it was recorded, but also upon acoustic frequency. For low‐frequency acoustic signals (below 700 Hz), the increment in CM was greatest at turn I and decreased toward the apex. At 5 kHz, COCB stimulation produced no detectable increment in CM at turn I. The reduction in discharges of auditory nerve fibers produced by COCB stimulation was greatest (16–20 dB in titration) when best frequency lay between 7 and 10 kHz. As best frequency decreased, the reduction in discharge rate with COCB stimulation decreased. Nerve fibers with very high best frequencies also showed minimal COCB effects. These data are discussed in relation to other recent information.