Rennie K J, Ashmore J F, Correia M J
Department of Physiology, University of Bristol, United Kingdom.
Am J Physiol. 1997 Dec;273(6):C1972-80. doi: 10.1152/ajpcell.1997.273.6.C1972.
In amniotes, there are two types of hair cells, designated I and II, that differ in their morphology, innervation pattern, and ionic membrane properties. Type I cells are unique among hair cells in that their basolateral surfaces are almost completely enclosed by an afferent calyceal nerve terminal. Recently, several lines of evidence have ascribed a motile function to type I hair cells. To investigate this, elevated external K+, which had been used previously to induce hair cell shortening, was used to induce shape changes in dissociated mammalian type I vestibular hair cells. Morphologically identified type I cells shortened and widened when the external K+ concentration was raised isotonically from 2 to 125 mM. The shortening did not require external Ca2+ but was abolished when external Cl- was replaced with gluconate or sulfate and when external Na+ was replaced with N-methyl-D-glucamine. Bumetanide (10-100 microM), a specific blocker of the Na(+)-K(+)-Cl- cotransporter, significantly reduced K(+)-induced shortening. Hyposmotic solution resulted in type I cell shape changes similar to those seen with high K+, i.e., shortening and widening. Type I cells became more spherical in hyposmotic solution, presumably as a result of a volume increase due to water influx. In hypertonic solution, cells became narrower and increased in length. These results suggest that shape changes in type I hair cells induced by high K+ are due, at least in part, to ion and solute entry via an Na(+)-K(+)-Cl- cotransporter, which results in cell swelling. A scheme is proposed whereby the type I hair cell depolarizes and K+ leaves the cell via voltage-dependent K+ channels and accumulates in the synaptic space between the type I hair cell and calyx. Excess K+ could then be removed from the intercellular space by uptake via the cotransporter.
在羊膜动物中，存在两种类型的毛细胞，分别称为I型和II型，它们在形态、神经支配模式和离子膜特性方面存在差异。I型细胞在毛细胞中独一无二，因为它们的基底外侧表面几乎完全被传入的杯状神经末梢所包围。最近，有几条证据表明I型毛细胞具有运动功能。为了对此进行研究，使用先前用于诱导毛细胞缩短的细胞外高钾来诱导离体哺乳动物I型前庭毛细胞的形态变化。当细胞外钾浓度从2 mM等渗升高到125 mM时，形态学鉴定的I型细胞会缩短并变宽。这种缩短不需要细胞外钙，但当细胞外氯离子被葡萄糖酸盐或硫酸盐取代，以及细胞外钠离子被N-甲基-D-葡萄糖胺取代时，缩短现象就会消失。布美他尼（10 - 100 μM），一种钠钾氯共转运体的特异性阻滞剂，显著降低了钾诱导的缩短。低渗溶液导致I型细胞形态变化，类似于高钾时观察到的变化，即缩短和变宽。在低渗溶液中，I型细胞变得更接近球形，推测是由于水流入导致体积增加的结果。在高渗溶液中，细胞变窄并变长。这些结果表明，高钾诱导的I型毛细胞形态变化至少部分是由于通过钠钾氯共转运体的离子和溶质进入，这导致细胞肿胀。提出了一个机制，即I型毛细胞去极化，钾离子通过电压依赖性钾通道离开细胞并积聚在I型毛细胞和杯状细胞之间的突触间隙中。然后过量的钾离子可以通过共转运体摄取从细胞间空间中去除。
