RAPID COMMUNICATION Ionic Currents and Electromotility in Inner Ear Hair Cells From Humans

Oghalai, John S., Jeffrey R. Holt, Takashi Nakagawa, Thomas have been studied in fish, amphibians, reptiles, birds, and M. Jung, Newton J. Coker, Herman A. Jenkins, Ruth Anne rodents (Eatock and Rüsch 1997; Kros 1996; Wu et al. Eatock, and William E. Brownell. Ionic currents and electromoti1995), and electromotility has only been demonstrated in lity in inner ear hair cells from humans. J. Neurophysiol. 79: 2235– rodent outer hair cells. These data have been used to explain 2239, 1998. The upright posture and rich vocalizations of primates diverse aspects of the senses of balance and hearing in huplace demands on their senses of balance and hearing that differ mans. However, there has been no study of living hair cells from those of other animals. There is a wealth of behavioral, psyfrom humans or other primates. Without such data, we canchophysical, and CNS measures characterizing these senses in prinot be certain of the relevance of detailed electrophysiologimates, but no prior recordings from their inner ear sensory receptor cal accounts of animal hair cells to human inner ear function. cells. We harvested human hair cells from patients undergoing surgical removal of life-threatening brain stem tumors and meaThis is of particular concern when attempting to understand sured their ionic currents and electromotile responses. The hair human pathophysiology. We investigated the extent to which cells were either isolated or left in situ in their sensory epithelium the physiology of primate hair cells resembles the physiology and investigated using the tight-seal, whole cell technique. We of nonprimate hair cells. recorded from both type I and type II vestibular hair cells under Because of the inaccessibility of the primate inner ear, voltage clamp and found four voltage-dependent currents, each of harvesting this tissue and keeping it alive is a difficult underwhich has been reported in hair cells of other animals. Cochlear taking. Sacrifice of the human inner ear is occasionally reouter hair cells demonstrated electromotility in response to voltage quired during surgical removal of tumors of the temporal steps like that seen in rodent animal models. Our results reveal bone and posterior cranial fossa. These are most often unilatmany qualitative similarities to hair cells obtained from other anieral vestibular schwannomas (incidence 1/100,000/yr) (Tos mals and justify continued investigations to explore quantitative differences that may be associated with normal or pathological and Thomsen 1984), where the wide exposure provided by human sensation. drilling out the inner ear aids tumor dissection. We were able to harvest inner ear organs from this select patient population, in which hearing and vestibular sense cannot be preI N T R O D U C T I O N served.