Calcium Transport in the Endolymphatic Space of Cochlea and Vestibular Organ

Abstract

Ca++ concentrations and d.c. potential within the endolymphatic space of the cochlear duct and the semicircular canal following acute anoxia or ethacrynic acid intoxication (100 mg/kg i.v.) were measured by means of double-barrelled microelectrodes. Ionic calcium content and d.c. potential were found to change in a roughly biphasic fashion after either intervention. The maximal increase in Ca++ concentration coincided with the decline in the d.c. potential, which after a rapid decline finally reached and maintained negative voltages. This phenomenon was more pronounced in the cochlear part than in the semicircular canal. A model of calcium homeostasis is proposed in an attempt to reconcile the data presented with earlier evidence.

Functional significance of channels and transporters expressed in the inner ear and kidney

“…Furthermore, Ca 2ϩ homeostasis of vestibular endolymph during development affects the formation of otoconia, which are necessary for the detection of gravity and linear acceleration (106,152). Consistent with the importance of Ca 2ϩ homeostasis in the endolymph are the observations that mice and guinea pigs with reduced or elevated endolymphatic Ca 2ϩ concentrations are deaf and have vestibular deficits (120,185,315,324).…”

“…For cochlear inner and outer hair cells, the driving force for sensory transduction is 120 mV (Ϫ40 mV ϩ 80 mV) and 150 mV (Ϫ70 mV ϩ 80 mV), respectively (38,189). Driving forces for sensory transduction in the vestibular labyrinth are smaller due to the smaller endovestibular potential of 3-7 mV (130,185,220).…”

The selectivity of the hair cell’s mechanoelectrical-transduction channel promotes Ca 2+ flux at low Ca 2+ concentrations

“…In hearing organs, the Ca 2ϩ concentration has been estimated to be as low as 30 M in mammals (5)(6)(7)(8) and 65 M in reptiles (9). In vestibular organs, the Ca 2ϩ concentration is higher than in the cochlea: it measures Ϸ100 M in the guinea pig's sacculus and utriculus (6) and Ϸ250 M in the guinea pig's semicircular canal (7,8) and the bullfrog's sacculus (10). Tight junctions between epithelial cells maintain the distinct ionic compositions of endolymph and perilymph (reviewed in ref.…”