Immunohistochemical localization of Ca2+/calmodulin-dependent protein kinase IV in outer hair cells

A smooth membrane system consisting of subsurface cisternae (SSC) underlies the lateral plasmalemma of auditory outer hair cells (OHCs). The SSC conta in Ca-ATPase and are regarded as an intracellular Ca2+ reservoir like the s arcoplasmic reticulum of myocytes. Recently, it has been demonstrated that Ca-ATPase activity in sarcoplasmic reticulum is regulated by Ca2+/calmoduli n-dependent protein kinases (CaM kinases). Here we investigated the presenc e of CaM kinases in OHCs and their possible association with the SSC. inner ears collected from adult gerbils and from neonates at 2-day intervals bet ween 0 and 20 days after birth were immunostained with antibodies specific for different CaM kinases. A polyclonal antiserum against CaM kinase IV yie lded a strong immunostaining reaction along the lateral wall of OHCs. The s taining appeared after the tenth postnatal day and continued into adulthood . No other site in the inner ear, including cochlear inner hair cells and v estibular hair cells, was reactive. The kinase's apparent association with the SSC strongly supports its involvement in intracellular Ca-2 divided by homeostasis and suggests a role in regulating the OHCs' slow motile respons es.