Calcium gradients in inner ear endolymph.

Recent studies suggest that endolymphatic hydrops resulting from the ablation of the endolymphatic duct and sac in guinea pigs may be caused by a disturbance of endolymph calcium homeostasis. A similar disturbance of calcium homeostasis could represent the underlying cause of Ménière's disease. In this study, we mapped the calcium concentrations and electrical potentials throughout the endolymphatic system in normal guinea pigs. Large concentration differences exist between different compartments, including a more than twofold increase along the length of the cochlea. The electrochemical potential for calcium (the force driving passive longitudinal calcium movement) was calculated for all the endolymphatic compartments. The results show that endolymph is extremely inhomogenous with respect to calcium potentials. On the basis of these potentials, it appears that calcium is transported into endolymph in the cochlea and out of endolymph in the saccule and utricle. The possibility that endolymphatic hydrops arises from a disturbance in longitudinal flow of calcium, rather than in longitudinal volume flow, is considered.