Jørgensen F, Kroese A B
IMB, Department of Physiology, Odense University, Denmark.
Acta Physiol Scand. 1995 Dec;155(4):363-76. doi: 10.1111/j.1748-1716.1995.tb09986.x.
The extracellular receptor currents evoked by step displacements of the otolithic membrane of the isolated saccular macula of Rana esculenta were recorded under transepithelial voltage clamp conditions. With the aim to depolarize the hair cells and increase the fractional resistance of the apical membranes, the basal side of the preparation was bathed in saline with an increased K+ concentration (62 mM). This caused a shift in the non-linear receptor current-voltage relation along the voltage axis of -51 mV +/- 10 mV; (mean +/- SD; n = 32) and a reduction in the transepithelial resistance of 10%. Under these conditions the electrical properties of the macula are assumed to be controlled by the apical membranes. The effects of different concentrations of Ca2+ in the apical solution on the receptor current-voltage relation were examined. Change of the apical Ca2+ concentration (range 3 mM to 70 microM) varied the transepithelial voltage at which the receptor current was zero (Vrev). Fitting a modified constant field equation to the relation between the apical Ca2+ concentration and the change in Vrev gave an estimate of PCa/PK of the transduction channels of 212. Furthermore, a high relative permeability of the transduction channels for other divalent cations (Ba2+, Sr2+) was measured, whereas Mn2+ inhibited the receptor current. The receptor current was inhibited by amiloride (IC50 3.2 microM +/- 1.7 microM) and nifedipine (IC50 1.9 microM +/- 0.6 microM). Reduction of the apical Ca2+ concentration to 90 microM in standard apical solution reduced the size of the receptor current to 67% +/- 30% (n = 17) compared to control but did not affect the shape of the receptor current-voltage relation. Subsequent substitution of K+ by Na+ caused a further reduction of the receptor current to 32% +/- 29% (n = 9), changed the receptor current-voltage relation into a linear relation and diminished the adaptation of the receptor current. These results indicate that the mechano-electrical transduction channels of the frog saccular hair cells are highly selective to Ca2+ and that the conductance of the channels may be influenced by the apical monovalent cation species.
在跨上皮电压钳制条件下，记录了食用蛙分离的球囊斑耳石膜阶跃位移诱发的细胞外受体电流。为了使毛细胞去极化并增加顶端膜的分数电阻，将标本的基底侧浸泡在钾离子浓度增加（62 mM）的盐溶液中。这导致非线性受体电流-电压关系沿电压轴负向移动了-51 mV±10 mV；（平均值±标准差；n = 32），跨上皮电阻降低了10%。在这些条件下，假定斑的电学特性由顶端膜控制。研究了顶端溶液中不同浓度的Ca2+对受体电流-电压关系的影响。顶端Ca2+浓度的变化（范围为3 mM至70 μM）改变了受体电流为零时的跨上皮电压（Vrev）。将修正的恒定场方程拟合到顶端Ca2+浓度与Vrev变化之间的关系，得出转导通道的PCa/PK估计值为212。此外，还测量了转导通道对其他二价阳离子（Ba2+、Sr2+）的高相对通透性，而Mn2+抑制受体电流。受体电流受到amiloride（IC50 3.2 μM±1.7 μM）和硝苯地平（IC50 1.9 μM±0.6 μM）的抑制。在标准顶端溶液中将顶端Ca2+浓度降低至90 μM时，与对照相比，受体电流大小降低至67%±30%（n = 17），但不影响受体电流-电压关系的形状。随后用Na+替代K+导致受体电流进一步降低至32%±29%（n = 9），将受体电流-电压关系转变为线性关系，并减弱了受体电流的适应性。这些结果表明，蛙球囊毛细胞的机械电转导通道对Ca2+具有高度选择性，并且通道的电导可能受到顶端单价阳离子种类的影响。
