Ultrastructural study of striated organelles in vestibular sensory cells of human fetuses.

The presence of striated organelles in the vestibular receptor of human fetuses of 10 to 22 weeks gestation was investigated. They were very frequent under the cuticular plate of the sensory cells, especially in type-I hair cells. Cross-sections of striated organelles showed that there were twice as many filaments in the dark bands as in the light bands. These filaments were often arranged in broken lines. Striated organelles were frequently associated with microtubules, mitochondria, and endoplasmic reticulum, and were fused with the plasma membrane forming an incomplete ring in the cytoplasm of the cells. We discuss the possibility that in adults, these striated organelles participate in an active mechanism that regulates the transduction of stimuli by means of a feedback control of the apical part of the calyx.