Voltage-Dependent Currents in Merkel Cell

用荧光染料醌预处理10 ~ 20日龄大鼠脚垫表皮，用酶解法分离默克尔细胞进行染色。采用传统膜片钳技术在全戴尔配置下进行电记录。荧光默克尔细胞静息膜电位平均值为-54.0 mV，高于非荧光表皮细胞的-26.1 mV。在外部标准溶液中，默克尔细胞没有Na^+尖峰，但在含有Ba^<2+>的外部溶液中注入恒电流去极化可诱发河豚毒素抗性持久动作电位。在电压箝位下的Merkel细胞中，保持电位（V_H）为-80 mV的去极化阶跃脉冲主要引发由瞬态和持续组分组成的外向K^+电流：前者被4-氨基吡啶（4-AP）选择性抑制，而后者则被选择性抑制。四乙基铵（TEA）和四乙基铵(qu…在V^H为-50 mV时，持续向外K^+电流（I_<KD>）在大于-20或-10 mV的电位下被激活，瞬时向外K^+通道在此电位下完全失活。在V_H为- 80mv时，瞬时外向K^+电流（I_A）在大于- 50mv的电位下被激活。当同时加入TEA和4-AP阻断向外的K^+电流时，只观察到持续向内的Ca^<2+>电流。在含有10 mM-Ca^<2+>的外溶液中，在V^H为-80 mV时，I_<ca>被大于-20 mV的电位激发，最大内向电流出现在+10 mV左右。外部Ca^<2+>浓度的增加引起I_< Ca >的双曲线增加。Ca^<2+>通道对二价阳离子的选择性顺序为Ba^<2+> > Sr^<2+> > Ca^<2+>。结果表明，默克尔细胞至少有三种不同的电压门控电流：延迟K^+电流（I_<KD>），瞬态a电流（I_A）和高阈值（l型）Ca^<2+>电流（I_< Ca >）。少

Merkel cells were dissociated enzymatically from the footpad epidermis of 10 to 20-day-old rats pretreated with fluorescent dye, quinacrine, for purposes of staining. Electrical recordings were performed in whole-dell configuration using a conventional patch-clamp technique. The mean resting membrane potential of fluorescent Merkel cells was -54.0 mV, the value being greater than the -26.1 mV of non-fluorescent epidermal cells. The Merkel cells had no Na^+ spike in an external standard solution, but tetrodotoxin-resistant long-lasting action potentials were evoked by depolarization with injection of constant currents in an external solution containing Ba^<2+>. In Merkel cells under voltage-clamp, depolarizing step pulses from a holding potential (V_H) of -80 mV elicited predominantly outward K^+ currents composed of transient and sustained components : the former was selectively inhibited by 4-aminopyridine (4-AP), while the latter. was inhibited by both tetraethylammonium (TEA) and qu … More inacrine. The sustained outward K^+ current (I_<KD>) was activated at potentials more positive than -20 or -10 mV at a V^H of -50 mV, at which potential the transient outward K^+ channel was completely inactivated. The transient outward K^+ current (I_A) was activated at potentials more positive than -50 mV at a V_H of -80 mV. When the outward K^+ currents were blocked by adding both TEA and 4-AP, only a sustained inward Ca^<2+> current was observed. In an external solution containing 10 mM-Ca^<2+>, I_<ca> was evoked by potentials more positive than -20 mV at a V^H of -80 mV, and the maximum inward current appeared around +10 mV. Increases of external Ca^<2+> concentration induced a hyperbolic increase of I_<ca>. The selectivity of the Ca^<2+> channel for divalent cations was in the order of Ba^<2+> > Sr^<2+> > Ca^<2+>. It was concluded that Merkel cells have at least three distinct voltage-gated currents : a delayed K^+ current (I_<KD>), a transient A current (I_A) and a high-threshold (L-type) Ca^<2+> current (I_<ca>). Less