Evans M G, Lagostena L, Darbon P, Mammano F
MacKay Institute of Communication and Neuroscience, School of Life Sciences, Keele University, STAFFS, ST5 5BG, UK.
Cell Calcium. 2000 Sep;28(3):195-203. doi: 10.1054/ceca.2000.0145.
We have studied the action of cholinergic agonists on outer hair cells, both in situ and isolated from the cochlea of the guinea pig, combining new fast CCD technology for Ca2+ imaging and conventional patch-clamp methods. Carbachol (1 mM) activated a current with a reversal potential near -70 mV and a bell-shaped I-V curve, suggesting that it was a Ca2+ activated K+ current. In a few cells, this current was preceded by a transient inward current, probably owing to an influx of Ca2+ and other cations through the acetylcholine (ACh) receptors. The amplitude of the Ca2+ signal was maximal in a circumscribed region at the basal pole of the cell and decreased steeply towards the apical pole, compatible with Ca2+ influx and/or Ca2+ induced Ca2+ release at the cells base. The time course of the Ca2+ rise was fastest at the base, but it was still slightly slower, and more rounded, than that of the K+ current. In some recordings the K+ current was observed without any measurable change of intracellular Ca2+. The K+ current was potentiated (18%) by caffeine (5 mM), and decreased (19%) by ryanodine (0.1 mM) in the majority of cells tested. The results are discussed in terms of a labile intracellular Ca2+ store located at the base of the cell, close to the Ca2+ permeable ACh receptor channels and Ca2+ activated K+ channels, whose contribution to the Ca2+ rise occurring in the region of the channels is variable, and probably dependent on its ability to refill with Ca2+.
我们结合用于Ca2+成像的新型快速电荷耦合器件（CCD）技术和传统膜片钳方法，研究了胆碱能激动剂对豚鼠耳蜗原位及分离的外毛细胞的作用。卡巴胆碱（1 mM）激活了一种电流，其反转电位接近 -70 mV，电流-电压（I-V）曲线呈钟形，表明这是一种Ca2+激活的K+电流。在少数细胞中，该电流之前有一个短暂的内向电流，可能是由于Ca2+和其他阳离子通过乙酰胆碱（ACh）受体流入所致。Ca2+信号的幅度在细胞基极的一个限定区域最大，并向顶极急剧下降，这与细胞基部的Ca2+内流和/或Ca2+诱导的Ca2+释放相一致。Ca2+上升的时间进程在基部最快，但仍比K+电流略慢且更圆润。在一些记录中，观察到K+电流而细胞内Ca2+没有任何可测量的变化。在大多数测试细胞中，咖啡因（5 mM）使K+电流增强（18%），而ryanodine（0.1 mM）使其降低（19%）。根据位于细胞基部、靠近Ca2+可渗透的ACh受体通道和Ca2+激活的K+通道的不稳定细胞内Ca2+储存来讨论这些结果，其对通道区域发生的Ca2+上升的贡献是可变的，并且可能取决于其重新填充Ca2+的能力。
