Effects of hypothermia on ionic movement in the guinea pig cochlea

Anesthetized and immobilized guinea pigs were subjected to hypothermia. During cooling, the cochlear microphonics and endocochlear potential decreased and K+ concentrations in both endolymph and perilymph were not significantly affected. The rate constant for K+ turnover to endolymph was determined by uptake of 43K into the endolymph when the perilymphatic space was perfused with artificial perilymph containing 43K. The rate constant for K+ decreased significantly in hypothermic guinea pigs when compared with that in normal guinea pigs. The K+ conductance of the endolymph-perilymph barrier, estimated from the rate constant, showed a marked decrease in hypothermic guinea pigs and was comparable with the K+ conductance, calculated from the rate of change of the endolymph K+ concentrations relative to the K+ electrochemical potential difference, recorded during permanent anoxia. These results suggest that hypothermia not only suppresses the active K+ transport system but also decreases the K+ permeability of the endolymph-perilymph barrier.