Distribution of ionocytes in the saccular epithelium of the inner ear of two teleosts ( Oncorhynchus mykiss and Scophthalmus maximus)

Abstract

The saccular membranes of trout (Oncorhynchus mykiss) and turbot (Scophthalmus maximus) were examined to characterize specialized epithelial cells that might be responsible for ion exchange. The approach for localizing cell types was new for this tissue, as observations were made with a stereomicroscope and a light microscope in order to have a general view of the epithelium. No important differences between the two species were seen. The saccular tissue is a monolayer epithelium (except for the macula neural zone) surrounded by a layer of connective tissue invaded by many blood vessels. The use of the fluorescent probe DAPSMI and zinc iodide/osmium fixation-coloration defined two areas in which ionocytes were present. In the first, large ionocytes were grouped into a nearly complete, crowned meshwork around, but separated from, the macula. In the second area, opposite the macula, the ionocytes were smaller, cubical, and grouped in patches. Cells rich in Na+, K+-ATPase and carbonic anhydrase II were present in both areas. Contrary to previous studies in mammals and fish, ionocytes were also found in the epithelium of the saccule.

Relationships between inner ear and sagitta growth during ontogenesis of three Carapini species, and consequences of life-history events on the otolith microstructure

“…This process has been corroborated by recent studies dealing with the various cellular types of the saccular epithelium (Mayer-Gostan et al 1997; Takagi Illustration of the different zone patterns (black arrow zone 2 postmetamorphic mark; white arrows zone 3 checks; discontinuous double black arrows opaque bands; continuous double black arrows translucent bands; An-Di antero-distal axes) 1997, 2000aPisam et al 1998). Depending on the species, variation in distribution within this epithelium of cellular ionic pumps (Mayer-Gostan et al 1997;Tohse and Mugiya 2001) and of secretory cells (Payan et al , 1999 led to a solute gradient, the formation of which interfered with otolith bio-calcification by favouring deposition on the proximal side (e.g. in turbot, Scophthalmus maximus, Payan et al 1999) or on the otolith edge, as in trout (Oncorhynchus mykiss, Payan et al 1999;Takagi and Takahashi 1999;Takagi 2000b).…”

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

“…Ionocytes have been found throughout the fish labyrinth (Mayer-Gostan et al, 1997) and have been specifically localized to the wall of the utricle and the common crus in the semicircular canals (Becerra and Anadon, 2003) and the wall of the saccule (Mayer-Gostan et al, 1997). These cells are thought to maintain the ionic gradient between endolymph, perilymph, and cranial fluid and are shown to contain large mitochondria and a membrano-tubular system in which Na ϩ /K ϩ -ATPase is located (Mayer-Gostan et al, 1997).…”

“…These cells are thought to maintain the ionic gradient between endolymph, perilymph, and cranial fluid and are shown to contain large mitochondria and a membrano-tubular system in which Na ϩ /K ϩ -ATPase is located (Mayer-Gostan et al, 1997). Fish endolymph is typically higher in sodium than is mammalian endolymph, and cranial fluids are normally close in ionic composition to plasma (Mayer-Gostan et al, 1997). This study revealed a significant difference between fish and mammals in the Na ϩ and K ϩ gradients across the hair-cell epithelium and, consistent with previous studies, higher sodium levels in endolymph.…”

“…The cellular machinery responsible for maintaining the ionic gradient between endolymph and perilymph differs between fish and mammals and, in the same animal, between organs (Marcus and Marcus, 1987;Marcus and Shen, 1994;Wangemann, 1995;Mayer-Gostan et al, 1997). The endolymphatic potential is generally positive with respect to the perilymph, though the difference varies between organs, ranging from ϩ80 mV in the mammalian cochlea to -10 mV in fish semicircular canals (Mayer-Gostan et al, 1997;Rabbitt et al, 2005). This is not surprising given the inter-species variability in fluid ionic composition and regulatory mechanisms found throughout the inner ear (Salt and Thalmann, 1988).…”

“…Much like the epithelial cells of the renal tubules, bladder, and sweat glands, the sensory hair cells of the inner ear are juxtaposed between two different fluids: endolymph, an unusual extracellular fluid, has high K ϩ and low Na ϩ concentrations in mammals and bathes the apical surface of the hair cells; perilymph, resembling cerebrospinal fluid, bathes the basolateral surfaces. The unique ionic composition of endolymph is thought to be maintained by the stria marginal cells and vestibular dark cells in mammals (Marcus and Marcus, 1987;Marcus and Shen, 1994;Wangemann, 1995) and ionocytes in fish (Mayer-Gostan et al, 1997). The electrochemical gradient between the two major extracellular compartments and the intracellular space drives ionic current flow through the various ion channels in sensory hair cells and is fundamental for the function of the inner ear organs.…”