LOCALIZATION OF CA-ATPASE IN FROG CRISTA-AMPULLARIS

THE distribution of Ca-ATPase in frog crista ampullaris was mapped ult racytochemically by using a one-step lead citrate reaction. Electron-d ense precipitates, as an expression of Ca-ATPase activity, were observ ed on the surface of stereocilia and on the apical membrane surroundin g the cuticular plate of hair cells. Sensory cells of the isthmus regi on showed more reactivity than those of the peripheral regions of the crista. No reaction products were detectable on the basolateral membra nes and in cytoplasmatic organelles. Supporting cells of the crista sh owed a quite variable Ca-ATPase reaction on microvilli and on basolate ral membranes. The presence of an evident reactivity on the stereocili a is consistent with the existence of an apical calcium microdomain in volved in the mechano-transduction process and supports the current vi ew that calcium ions enter the stereocilia during natural stimulation. On the other hand, the lack of an observable reactivity on the basola teral membrane of hair cells suggests that in semicircular canals othe r mechanisms of active transport of calcium ions across the plasma mem brane, such as Na-Ca exchange, may be involved in homeostasis of the i on. (C) 1998 Rapid Science Ltd.