CA2+-ATPASES IN THE COCHLEAR DUCT

Differing levels of the Ca2+-ATPase enzymes that reside on the plasma membrane (PM) and on the endoplasmic reticulum (ER) were identified in individual rat cochlear tissues by the use of a semi-quantitative enz yme-linked immunosorbent assay (ELISA). Unlike other studies, a specif ic antibody to PM Ca2+-ATPase was used to detect significantly greater levels (about 2x) of PM Ca2+-ATPase in the stria vascularis (SV) than that in the spiral ligament (SL) and organ of Corti (OC) tissues. Sim ilarly, levels of ER Ca2+-ATPase were also significantly higher in the SV than in the SL and OC tissues. The presence of ER Ca2+-ATPase in t he tissues of the SV has not been demonstrated previously. Given the i mportance of Ca2+ homeostasis in the inner ear, the statistically sign ificantly higher densities of both PM and ER Ca2+-ATPase measured in t he SV relative to the SL and OC regions would indicate tissue-specific responses to fluctuations in systemic and local Ca2+ concentrations.