Masetto Sergio, Zampini Valeria, Zucca Giampiero, Valli Paolo
Dipartimento di Scienze Fisiologiche-Farmacologiche Cellulari-Molecolari, Sez. di Fisiologia Generale e Biofisica Cellulare, Università di Pavia, Via Forlanini 6, 27100 Pavia, Italy.
Pflugers Arch. 2005 Nov;451(2):395-408. doi: 10.1007/s00424-005-1466-7. Epub 2005 Aug 16.
Type I and Type II hair cells, and Type II hair cells located in different zones of the semicircular canal crista, express different patterns of voltage-dependent K channels, each one specifically shaping the hair cell receptor potential. We report here that, close to hatching, chicken embryo semicircular canal Type I and Type II hair cells express a similar voltage-dependent L-type calcium current (I(Ca)), whose main features are: activation above -60 mV, fast activation kinetics, and scarce inactivation. I(Ca) should be already active at rest in Zone 1 Type II hair cells, whose resting membrane potential was on average slightly less negative than -60 mV. Conversely, I(Ca) would not be active at rest in Type II hair cells from Zone 2 and 3, nor in Type I hair cells, since their resting membrane potential was significantly more negative than -60 mV. However, even small depolarising currents would activate I(Ca) steadily in Zone 2 and 3 Type II hair cells, but not in Type I hair cells because of the robust repolarising action of their specific array of K(+) currents. The implications of the present findings in the afferent discharge are discussed.
I型和II型毛细胞，以及位于半规管嵴不同区域的II型毛细胞，表达不同模式的电压依赖性钾通道，每种通道都特异性地塑造毛细胞受体电位。我们在此报告，在接近孵化时，鸡胚半规管I型和II型毛细胞表达相似的电压依赖性L型钙电流（I(Ca)），其主要特征为：在-60 mV以上激活、快速激活动力学以及极少失活。I(Ca)在1区II型毛细胞静息时应已激活，其静息膜电位平均略高于-60 mV的负值。相反，I(Ca)在2区和3区的II型毛细胞以及I型毛细胞静息时不会激活，因为它们的静息膜电位显著高于-60 mV的负值。然而，即使是小的去极化电流也会在2区和3区的II型毛细胞中稳定地激活I(Ca)，但在I型毛细胞中不会，因为其特定的钾电流阵列具有强大的复极化作用。本文讨论了这些发现对传入放电的影响。
