Mammalian vestibular epithelia are characterized by the expression of two different sensory cells named Type I and Type II hair cells. Different from Type II cells, the basolateral membrane of Type I cells shows two distinguishing properties: it is entirely wrapped by a single nerve terminal, called the calyx, and it expresses a low-voltage-activated outward rectifying K+ current, IK,L which is responsible for the much lower input resistance at rest as compared to Type II hair cells. Strikingly, the principal biophysical features of IK,L have not been unequivocally described so far. In fact, its voltage- and time-dependent properties have been reported to vary widely not only among Type I hair cells, but also in the same cell over time. On the basis of our electrophysiological recordings from in situ and dissociated mouse crista Type I cells, we showed that the large variability in IK,L properties is attributable to different degrees of K+ accumulation in the narrow space of the synaptic cleft between the hair cell and the residual calyx. Hence, in order to obtain a genuine description of IK,L, we developed a procedure to refine the removal of the calyx prior to patching. Only once the calyx had been effectively removed could we show that the biophysical properties of IK,L are in fact consistent among cells, and quite constant during the recordings. In particular, IK,L showed significantly slower deactivation kinetics (time constant: ~1s at –80 mV), a less negative voltage activation (half-activation voltage: -69 mV) and a steeper voltage dependence (S: 3.72mV) than previously reported. In conclusion, our data provide for the first time a complete description of the authentic biophysical properties of IK,L. As a corollary, we demonstrate that the calyx represents a strong barrier to K+ diffusion out of the synaptic cleft, which provides a direct way to depolarize either the hair cells and their calyx.

Authentic biophysical properties of IK,L in mammalian vestibular type I hair cells revealed after calyx removal

SPAIARDI, PAOLO;TAVAZZANI, ELISA;MAGISTRETTI, JACOPO;RUSSO, GIANCARLO;PRIGIONI, IVO;MASETTO, SERGIO
2014-01-01

Abstract

Mammalian vestibular epithelia are characterized by the expression of two different sensory cells named Type I and Type II hair cells. Different from Type II cells, the basolateral membrane of Type I cells shows two distinguishing properties: it is entirely wrapped by a single nerve terminal, called the calyx, and it expresses a low-voltage-activated outward rectifying K+ current, IK,L which is responsible for the much lower input resistance at rest as compared to Type II hair cells. Strikingly, the principal biophysical features of IK,L have not been unequivocally described so far. In fact, its voltage- and time-dependent properties have been reported to vary widely not only among Type I hair cells, but also in the same cell over time. On the basis of our electrophysiological recordings from in situ and dissociated mouse crista Type I cells, we showed that the large variability in IK,L properties is attributable to different degrees of K+ accumulation in the narrow space of the synaptic cleft between the hair cell and the residual calyx. Hence, in order to obtain a genuine description of IK,L, we developed a procedure to refine the removal of the calyx prior to patching. Only once the calyx had been effectively removed could we show that the biophysical properties of IK,L are in fact consistent among cells, and quite constant during the recordings. In particular, IK,L showed significantly slower deactivation kinetics (time constant: ~1s at –80 mV), a less negative voltage activation (half-activation voltage: -69 mV) and a steeper voltage dependence (S: 3.72mV) than previously reported. In conclusion, our data provide for the first time a complete description of the authentic biophysical properties of IK,L. As a corollary, we demonstrate that the calyx represents a strong barrier to K+ diffusion out of the synaptic cleft, which provides a direct way to depolarize either the hair cells and their calyx.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11571/908034
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