Armstrong C E, Roberts W M
Institute of Neuroscience, University of Oregon, Eugene, Oregon 97403-1254, USA.
J Neurosci. 1998 Apr 15;18(8):2962-73. doi: 10.1523/JNEUROSCI.18-08-02962.1998.
Although it is widely accepted that the electrical resonance seen in many types of auditory and vestibular hair cells contributes to frequency selectivity in these sensory systems, unexplained discrepancies in the frequency (f) and sharpness (Q) of tuning have raised serious questions. For example, enzymatically dissociated hair cells from bullfrog (Rana catesbeiana) sacculus resonate at frequencies well above the range of auditory and seismic stimuli to which the sacculus is most responsive. Such disparities, in addition to others, have led to the proposal that electrical resonance alone cannot account for frequency tuning. Using grassfrog (Rana pipiens) saccular hair cells, we show that the reported discrepancies in f and Q in this organ can be explained by the deleterious effects of enzyme (papain) exposure during cell dissociation. In patch-clamp studies of hair cells in a semi-intact epithelial preparation, we observed a variety of voltage behaviors with frequencies of 35-75 Hz. This range is well below the range of resonant frequencies observed in enzymatically dissociated hair cells and more in tune with the frequency range of natural stimuli to which the sacculus is maximally responsive. The sharpness of tuning also agreed with previous studies using natural stimuli. In contrast to results from enzymatically dissociated hair cells, both a calcium-activated K+ (KCa) current and a voltage-dependent K+ (KV) current contributed to the oscillatory responses of hair cells in the semi-intact preparation. The properties of the KCa and the Ca2+ current were altered by enzymatic dissociation. KV and a small-conductance calcium-activated K+ current were apparently eliminated.
尽管人们普遍认为，在许多类型的听觉和前庭毛细胞中观察到的电共振有助于这些感觉系统的频率选择性，但调谐频率（f）和锐度（Q）中无法解释的差异引发了严重问题。例如，从牛蛙（Rana catesbeiana）球囊酶解分离的毛细胞在远高于球囊最敏感的听觉和地震刺激频率范围内发生共振。除其他差异外，这些差异导致了仅靠电共振无法解释频率调谐的提议。使用草蛙（Rana pipiens）球囊毛细胞，我们表明，该器官中报道的f和Q差异可以通过细胞解离过程中酶（木瓜蛋白酶）暴露的有害影响来解释。在半完整上皮制剂中对毛细胞进行膜片钳研究时，我们观察到了频率为35 - 75 Hz的各种电压行为。这个范围远低于酶解分离的毛细胞中观察到的共振频率范围，并且更符合球囊最大反应的自然刺激频率范围。调谐锐度也与先前使用自然刺激的研究结果一致。与酶解分离的毛细胞结果相反，钙激活钾离子（KCa）电流和电压依赖性钾离子（KV）电流都对半完整制剂中毛细胞的振荡反应有贡献。酶解分离改变了KCa和钙离子电流的特性。KV和小电导钙激活钾离子电流显然被消除了。
