Effects of hypothermia on ionic movement in the guinea pig cochlea

Anesthetized and immobilized guinea pigs were subjected to hypothermia. During cooling, the cochlea: 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⁺ concentration 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.