Microvillous cells in ampullae of the lizard inner ear

Electron microscopy of membranous labyrinths in Anolis carolinensis, Gonatodes biteanatus and Ameiva chrysolaema reveals the presences of cells of complex structure located adjacent to sensory areas in all ampullae. Microvillous cells are characterized by extensive infolding of basal cell membrane, with clefts extending to level of the basal portion of the nucleus. Each compartment thus formed is filled with mitochondria, ribosomes and glycogen. Lateral and basolateral interdigitations with surrounding cells are present. Supranuclear cytoplasm is composed of numerous mitochondria, extensive Golgi apparatus and dense populations of ribosomes and glycogen. Smooth endoplasmic reticulum is the most common reticulum present, although there is scattered granular reticulum. Toward lumen of ampulla, cells are constricted and a small portion of cytoplasm extends between supporting cells to bulge into lumen. Long, slender, branching microvilli project from luminal border into endolymph. Supporting cells resemble those found in adjacent sensory areas, with undulating luminal membranes, few mitochondria, scattered (but abundant) ribosomes and polysomes, considerable endoplasmic reticulum, extensive Golgi apparatus, lateral and basolateral interdigitations with other supporting cells and microvillous cells. Also present are large vacuoles containing elongate, randomly‐ oriented crystalline material. General morphology of microvillous cells suggests that they are involved in ion transport and in maintenance of electrolyte balance in endolymph. The role of glycogen in this process is discussed, as is the general problem of endolymph formation.