Masetto S, Russo G, Taglietti V, Prigioni I
Istituto di Fisiologia Generale, Sezione di Pavia, Università di Pavia.
Boll Soc Ital Biol Sper. 1991 May;67(5):493-500.
Hair cells of the inner ear are endowed with different types of ionic channels. To characterize voltage- and ion-dependent channels in vestibular hair cells, experiments were performed in enzymatically isolated hair cells of frog semicircular canals by using the whole-cell configuration of the patch-clamp technique. A large outward current, identified as a K+ current, was recorded when 132 mM KCl were present in the pipette filling solution. It could be dissected pharmacologically into three different components. The first component, which was transient and selectively blocked by 10 mM external 4AP, is most likely an IA-type current. The second one, sensitive to 20 mM external TEA, might be a delayed rectifier K+ current, while the third component insensitive to TEA and showing faster activation time course has been interpreted as a K+ current of IKCa-type. After blocking the outward current by substituting Cs+ for K+ and adding 20 mM TEA to the internal solution, a sustained inward current, identified as a Ca++ current, could be recorded. This current did not inactivate, and was blocked by Cd++ more effectively than Ni++, thus suggesting the presence of Ca++ channels similar to the neuronal "L" channels. Since both K+ and Ca++ channels were recruited at potentials near the resting level, it is suggested that they are involved in the modulation of the resting as well as the evoked transmitter release from the basal pole of the hair cells.
内耳的毛细胞具有不同类型的离子通道。为了表征前庭毛细胞中电压和离子依赖性通道，采用膜片钳技术的全细胞模式，在酶分离的青蛙半规管毛细胞中进行了实验。当移液管灌流液中含有132 mM KCl时，记录到一个大的外向电流，被确定为K+电流。它可以通过药理学方法分为三个不同的成分。第一个成分是瞬时性的，可被10 mM外部4AP选择性阻断，很可能是IA型电流。第二个成分对20 mM外部TEA敏感，可能是延迟整流K+电流，而第三个成分对TEA不敏感且显示出更快的激活时间进程，已被解释为IKCa型K+电流。在用Cs+替代K+并向内部溶液中加入20 mM TEA阻断外向电流后，可记录到一个持续的内向电流，被确定为Ca++电流。该电流不发生失活，并且被Cd++比Ni++更有效地阻断，因此表明存在类似于神经元“L”通道的Ca++通道。由于K+和Ca++通道在接近静息电位时被激活，提示它们参与调节毛细胞静息状态以及从其基底部诱发的递质释放。
