Inhibition on cochlear nerve fibers by the sound-activated olivocochlear bundle.

Cell motility was measured by the degree of the fluctuation of the light intensity which pass through optical microscope (X 150) observing systems. The photodiode was mounted on the eye-piece lense and its output was fed into the operational amplifier and finally connected to memory oscilloscope. The degree of cell motility was determined by the average amplitude of the intensity fluctuation caused by sperm moving. In Fig. I, the membrane potential (A 'I' ) of the sperm was plotted against the various concentration of potassium. Under the normal condition of incubation solution, the membrane potential of the sperm was about -20 mY, and it was decreased linearly with potassium concentration. Finally, it became nearly 0 when potassium concentration reached 200 mM. Under the same range of potassium concentrations, the intracellular pH was measured by using 31P_NMR. The results are shown in Fig. 2. From 10 mM to 40 mM of potassium concentration, the pHint was constant (=6.8) and then decreased linearly with K+ concentration. The same kind of decrease in pHint was also obtained when the pH of the incubation solution was changed to acidic (Fig. 3). In both cases, high K+ concentration (=200 mM) or low pH (=5.0) of external solution, pHint was decreased about 0.2 unit and surprisingly, cell motility was inhibited absolutely. From these results, we can conclude that external high potassium concentration led to the acidification of pHint and reached to the immobilization of sperm. The mechanism why high potassium resulted in low pHint and why pHint stops flagellum motion is not clear at present but it might be very convenient to assume the existence of H+-K+ exchange mechanism. Considering the simillarity in the structure of sperm flagellum and hair cell cillia,6) these results suggest that high potassium content in endolymph of cochlea might be necessary to inhibit self moving of the hair cell cilia and increase the sensitivity to the mechanical stimulation on it..