Chemical dissection of stereovilli from fish inner ear reveals differences from intestinal microvilli

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Abstract
A quick method was developed for isolating the stimulus-receiving apparatus (stereovilli=‘stereocilia’) from the vestibular apparatus of fish (Scardinius erythrophthalmus andRutilus rutilus) in sufficient quantity and purity to study the solubilities and stabilities of their structural elements by electron microscopy. The stereovilli were adsorbed to a support and, after various treatments, negatively stained or metal shadowed after freeze drying. For comparison, and in order to ensure the validity of the method, some experiments were similarly performed on intestinal microvilli from chicken. Microvilli adsorbed to a support gave similar results as in suspension. Stereovilli and microvilli are similar in their architecture, except for the specialized base of stereovilli, and in the Mg2+- or Ca2+-induced splaying of the actin cores. Major differences occur in the solubilities of the linkers which connect the actin core and the membrane (a-m-linkers). In contrast to microvilli, these linkers are removed from the stereovilli core together with the membrane by Triton-X-100. The linkers together with some membrane components are preserved by glutaraldehyde fixation prior to detergent extraction. In stereovilli, the position of the linkers is recognizable in fixed material. In microvilli the membrane contains so much material, which becomes detergent insoluble after glutaraldehyde fixation, that the linkers become completely obscured.