Measurement of Na+ Activity in Endolymph in Guinea Pig Cochlea with a Sodium Sensitive Glass Microelectrode
Measurement of the Na+ concentration of endolymph in guinea pig cochlea was investigated with a Na+ sensitive double-barrelled ion electrode. The Na+ sensitive exchanger, Fluka 71732, was poured into the tip of one of the double electrodes. The other electrode was filled with 0.5 M KC1 solution. Measurement of the Na+ diffusion potentials in the solutions containing different concentrations of Na+ indicated that the potential was directly proportional to the logarithm of the Na+ concentration with a slope of 37 to 45 mV per 10 times change in the Na+ concentration at 22-24℃. Electrodes having smaller potential change than 35 mV were abandoned. When a hypoxic condition was loaded on a guinea pig by stopping the respirator, EP declined rapidly and the Na+ concentration increased by about 13 mV, which corresponded to an increase of 1.65 mM in the Na+ concentration. The results indicate that our Na+ electrodes were constructed well enough to measure the Na+ activity in endolymph. The endolymphatic Na+ concentration is considered to increase as a result of inhibition of Na+-K+ATPase activity, which is located in the basolateral membrane of the marginal cells of the stria vascularis.