Prigioni I, Masetto S, Russo G, Taglietti V
Institute of General Physiology, University of Pavia, Italy.
J Vestib Res. 1992;2(1):31-9.
Some properties of Ca2+ currents in hair cells isolated from frog semicircular canals by enzymatic or mechanical treatment were studied by using the whole-cell configuration of the patch-clamp technique. After blocking the large outward K+ currents by substituting Cs+ for K+ and adding tetraethylammonium to the pipette filling solution, voltage- and time-dependent inward currents were clearly detectable in the presence of 4 mM Ca2+ in the extracellular solution. Ca2+ current was recruited at test potentials more positive than -60 mV, showed a rapid activation, and exhibited no inactivation during 150-ms depolarizing pulses. The maximal amplitude was attained at about -20 mV, with an average value of about 80 pA. When Ca2+ in the extracellular solution was replaced with Ba2+, the magnitude of inward currents increased about twofold. Ba2+ currents were blocked more effectively by Cd2+ than by Ni2+, were suppressed by 0.5 microM omega-conotoxin, and were virtually unaffected by amiloride. The dihydropyridine Bay K 8644 caused a marked voltage-dependent increase in inward currents. The present data suggest that hair cells from frog crista ampullaris are endowed with a homogeneous population of Ca2+ channels having several properties similar to those described for neuronal L channels. Since these channels are recruited in a range of potentials close to the resting level, it is suggested that they subserve the control of both resting and evoked transmitter release from the basal pole of the hair cells.
采用膜片钳技术的全细胞模式，研究了经酶解或机械处理从青蛙半规管分离出的毛细胞中Ca2+电流的一些特性。用Cs+替代K+并在微电极灌流液中加入四乙铵以阻断大的外向K+电流后，在细胞外溶液中存在4 mM Ca2+的情况下，可清晰检测到电压和时间依赖性内向电流。Ca2+电流在比 -60 mV更正的测试电位时被激活，表现出快速激活，并且在150 ms的去极化脉冲期间无失活现象。最大幅度在约 -20 mV时达到，平均值约为80 pA。当细胞外溶液中的Ca2+被Ba2+替代时，内向电流幅度增加约两倍。Ba2+电流被Cd2+阻断的效果比被Ni2+更有效，被0.5 microM ω-芋螺毒素抑制，并且几乎不受氨氯吡咪影响。二氢吡啶Bay K 8644使内向电流明显呈电压依赖性增加。目前的数据表明，青蛙壶腹嵴的毛细胞具有一群均匀的Ca2+通道，其具有一些与神经元L型通道相似的特性。由于这些通道在接近静息水平的一系列电位中被激活，提示它们参与控制毛细胞基部静息和诱发的递质释放。
