Effects of hypothermia on ionic movement in the guinea pig cochlea

Anesthetized guinea pigs were subjected to hypothermia. During cooling, cochlear microphonics and endocochlear potential decreased, but K+ and Na+ concentrations in both endolymph and perilymph were not significantly affected. The rate constant for K+ turnover 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 conductance calculated from the rate of change of the endolymph K+ concentration relative to the K+ electrochemical potential difference recorded during permanent anoxia. These results indicate that hypothermia not only suppresses the active K+ transport system but also decreases the K+ permeability of the endolymph-perilymph barrier.