Effect of neuroregulators on the intracellular calcium level in the outer hair cell isolated from the guinea pig

The cytosolic calcium concentration [( Ca2+]i) of the isolated outer hair cell of the guinea pig was measured using fluorescence imaging microscopy and the effects of efferent neuroregulators such as acetylcholine, ATP, GABA, substance P, enkephalin, calcitonin gene-related peptide, serotonin, dopamine, norepinephrine, and glutamate were investigated. Among the drugs tested only ATP induced an elevation of the [Ca2+]i of the outer hair cell. In the resting condition, [Ca2+]i averaged 104.5 +/- 31.1 nM (n = 27), while 100 microM ATP significantly increased [Ca2+]i to 146.3 +/- 43.5 nM (n = 19). Superfusion with Ca2(+)-free solution (pCa = 7.5) abolished the increase in [Ca2+]i induced by ATP, suggesting that ATP causes an entry of external Ca2+. The relevance of [Ca2+]i to the inhibitory actions of efferent neuroregulators is discussed.

Coexistence of substance P and calcitonin gene-related peptide-like immunoreactivities in the rat vestibular endorgans

The immunocytochemical distribution and coexistence of substance P (SP) and calcitonin gene-related peptide (CGRP) in the rat vestibular endorgans were investigated. SP-like immunoreactivity was found in nervous elements beneath and around hair cells. CGRP-like immunoreactivity was also abundantly distributed beneath and within the sensory epithelia. In the present study, double-staining immunocytochemistry revealed that three different types of immunoreactivities: SP-positive/CGRP-negative, SP-negative/CGRP-positive, and SP/CGRP-positive immunostaining can be distinguished. SP/CGRP-immunoreactive fibers were localized within as well as beneath the sensory epithelia. These fibers often penetrated the epithelia and nearly reached the surface. The present immunocytochemical evidence suggests that different types of peripheral nervous systems may exist in the vestibular periphery.

Carbohydrates of the vestibular end organs. An ultrastructural study using gold-labeled lectins

The presence of carbohydrates in the glycocalyx of the vestibular end organs of the guinea pig was investigated at the ultrastructural level using lectin-gold solutions. The glycocalyx of both the sensory and the supporting cells has variable sugar components. The glycocalyx of the sensory cells including the ciliary interconnections contains N-acetyl-glucosamine, galactose and mannose. In contrast, the glycocalyx of the supporting cells had a lower amount of N-acetylglucosamine. The ciliary interconnections, which have been considered to be a part of the glycocalyx, have larger amounts of galactose and mannose than the surface glycocalyx. These findings indicate that the sugar components may be closely related to the functional significance of the inner-ear glycocalyx and that the functional properties of the glycocalyx may differ between the sensory and the supporting cells of the vestibular end organs.

Ultrastructural study of cytochemical localization of carbonic anhydrase in the inner ear

Vibratome sections were stained for cytochemical localization of carbonic anhydrase (CA) activity in vestibular neuro-epithelium, spiral ligament and spiral limbus. The new finding is the localization of reaction products in the interdental cells of the spiral limbus, Claudius' cells, mesothelial cells of the lower border of spiral ligament, vestibular sensory cells and perilymphatic cells, which have not earlier been proved to have CA activity. The interdental cells showed the products only on the basolateral infoldings. Claudius' cells showed prominent products in the microvilli. In the vestibular sensory cells, the products were present only in the stereocilia and cuticular areas. The perilymphatic fibrocytes under the vestibular sensory epithelium, like the fibrocytes of the spiral ligament, revealed diffuse products throughout the whole cell. In the vestibular supporting cells and transitional cells, the reaction products were localized diffusely in the cytosol, but not in the secretory granules. In the long cell projections of the transitional cells, type II fibrocytes at spiral prominence, mesothelial cells at the uppermost region of the spiral ligament and Borghesan's zone, the localization of the reaction products was the same as that of the basolateral infoldings of the vestibular dark cells and marginal cells of stria vascularis shown previously.

Cytoskeletal network of intermediate filament proteins in the adult human vestibular labyrinth

The cytoskeleton of adult human vestibular hair cells lacks intermediate filament (IF) proteins, whereas in fetal material immunoreactivity for cytokeratin (cks; a subclass of IFs) occurs in both types of hair cells. The shift in the cytoskeletal composition can be hypothesized to their onset of physiological function. Since the IFs are extremely rigid intracellular structures, they provide considerable mechanical stability. The entire cytoplasm of all supporting cells in the epithelial lining of all five vestibular organs is filled with cks. In this way most vestibular hair cells become compartmentalized, each with a rigid shell surrounding it. The distinct delineation of IF proteins in adult tissues, in contrast to fetal inner ear organs in which often a rather general cytoplasmic expression occurs, probably reflects their anatomical basis for their function.