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Ionic Composition of Endolymph and Perilymph in the Inner Ear of the Oyster Toadfish, Opsanus tau

Tamer A. Ghanem^1,*, Kathryn D. Breneman¹, Richard D. Rabbitt^1,2, and H. Mack Brown³

¹ Department of Bioengineering, University of Utah, Salt Lake City, Utah 84112
² Marine Biological Laboratory, Woods Hole, Massachusetts 02543
³ Dept. of Physiology, University of Utah, Salt Lake City, Utah 84112

To whom correspondence should be addressed. E-mail: r.rabbitt{at}utah.edu

The concentrations of free Na⁺, K⁺, Ca²⁺, and Cl^-in endolymph and perilymph from the inner ear of the oyster toadfish, Opsanus tau, were measured in vivo using double-barreled ion-selective electrodes. Perilymph concentrations were similar to those measured in other species, while endolymph concentrations were similar to those measured previously in elasmobranch fish, though significantly different from concentrations reported in mammals. Perilymph concentrations (mean ± std. dev.) were as follows: Na⁺, 129 mmol l^-1 ± 20; K⁺, 4.96 mmol l^-1 ± 2.67; Ca²⁺, 1.83 mmol l^-1 ± 0.27; and Cl^-, 171 mmol l^-1 ± 20. Saccular endolymph concentrations were Na⁺, 166 mmol l^-1 ± 22; K⁺, 51.4 mmol l^-1 ± 16.7; Ca²⁺, 2.88 mmol l^-1 ± 0.27; and Cl^-, 170 mmol l^-1 ± 12; and semicircular canal (utricular vestibule) endolymph concentrations were Na⁺, 122 mmol l^-1 ± 15; K⁺, 47.7 mmol l^-1 ± 13.2; Ca²⁺, 1.78 mmol l^-1 ± 0.48; Cl^-, 176 mmol l^-1 ± 27. The relatively high concentrations of Ca²⁺ and Na⁺ in the endolymph may have significant implications for the physiological function of the mechanoelectrical transduction channels in the vestibular hair cells of fish compared to those of their mammalian counterparts.

Abbreviations: AE, artificial endolymph • AP, artificial perilymph • MET, mechanoelectrical transduction