Analysis of calcium ion transition in the cochlear fluids under cochlear blood flow disturbance

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Homeostasis of calcium ion (Ca^<2+>) activities in the cochlear fluids are considered to be essential to maintain the function of the cochlea. Since local ischemia in the inner ear could disrupt the homeostasis, Ca^<2+> activities in perilymph and endolymph were monitored during and after local ischemia induced by pressing a labyrinthine artery in the guinea pig. In 30-minute local ischemia, perilymph and endolymph Ca^<2+> activities increased approximately 1.5 and 4 times as much. as the preischemic values, respectively, After the blood flow was restored, the activities decreased close to the preischemic values in an exponential manner. An evident and reversible acidification of perilymph and endolymph was also noted during local ischemia but found not so contributory to the Ca^<2+> activity changes. On the other hand, utilizing compartment models and mathematical estimations, it was disclosed that Ca^<2+> transitions could be mostly explained by passive diffusion driven by electrochemical gradients. In this analytical procedure, the apparent permeability surface area product (PS product) of blood-perilymph barrier (BPB) for Ca^<2+> was assumed slightly larger than that of blood-brain barrier (BBB), and the perilymph turnover rate was computed to be about l.4mu l/min.