Regulation of inner ear fluid in the guinea pig cochlea after the application of saturated NaCl solution to the round window membrane

The regulation of K⁺ and Na⁺ in the inner ear fluid of the guinea pig was studied after the application of saturated NaCl solution to the round window membrane. K⁺ and Na⁺ activities in the scala tympani increased rapidly and then decreased. K⁺ activity in the scala media increased immediately, but Na⁺ activity continued to increase during the period of observation. K⁺ activity in the scala vestibuli continued to increase in the observation period. Na⁺ activity in the scala vestibuli increased and then decreased. The endocochlear potential decreased immediately to approximately 20% of its initial level. Total activities of K⁺ and Na⁺ increased immediately and then decreased in both the scala tympani and scala media. The total activity of K⁺ and Na⁺ increased slowly and showed no regulatory decrease in the scala vestibuli. Thus, changing patterns in the total activity of K⁺ and Na⁺ were similar for the scala tympani and scala media, but not for the scala media and the scala vestibuli. Different patterns of K⁺ and Na⁺ activities among the three scalae indicate that their mechanisms for regulating inner ear fluid differ.