Quantitative Differences in Endolymphatic Calcium and Endocochlear Potential Between Pigmented and Albino Guinea Pigs

Sarvjit S. Gill and Alec N. Salt

Abstract

A number of previous studies have suggested that melanin may play a role in Ca homeostasis of endolymph. In the present study, endolymph Ca levels and endocochlear potential (EP) were measured in all four cochlear turns of pigmented or albino guinea pigs. Auditory sensitivity was also evaluated using cochlear action potential thresholds. In pigmented animals we found that endolymph Ca tended to increase from base to apex of the cochlea, while EP systematically decreased towards the apex. In contrast, no significant Ca gradient was found in albinos and the EP decline was far less. As a result, the apical turn of albino animals had significantly lower Ca and significantly higher EP than in pigmented animals. AP thresholds pooled across all test frequencies were significantly lower in albino animals although no differences at individual frequencies reached significance. Even after correction for EP differences, the endolymph Ca levels in albino animals were significantly lower than in pigmented ones. These results confirm that there are significant physiologic differences between pigmented and albino animals, which are a likely consequence of the absence of melanin in the albino cochlea. They are consistent with the involvement of melanin in the active transport of Ca into endolymph.

This study was supported by the National Institutes of Health through the National Institute on Deafness and other Communication Disorders, Grant number DC01368

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