To determine whether any differences exist in potassium circulation between the scala vestibuli and scala tympani, we recorded the change in K+ activity in both scalae of the guinea pig cochlea at the basal and third turns, using a double-barrelled, K+-sensitive microelectrode after perfusion with artificial perilymph containing 20 m M KCl and 130 m M NaCl. K+ activity increased immediately after the start of perfusion and decreased after its completion. The rates of decrease of K+ activities were approximately 1.0 mEq/l per min in the scala vestibuli of the basal and third turns, also 1.0 mEq/l per min in the scala tympani of the basal turn, and approximately 0.5 mEq/l per min in the scala tympani of the third turn. The rate of decrease of K+ activity in the scala tympani was significantly slower in the third turn than in the basal turn. Blockage of the cochlear aqueduct depressed the rate of decrease of K+ activity in the scala tympani more in the basal turn than in the third turn. These results suggest that there is a difference in potassium circulation between the scala vestibuli and scala tympani, and that the cochlear aqueduct plays an important role in potassium circulation in the perilymph of the scala tympani.
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