Voltage-Dependent Currents in Merkel Cell

从10-20日龄大鼠的足垫表皮上用酶法分离出Merkel细胞，用荧光染料Quacine进行处理，以进行染色。使用传统的膜片钳技术在全戴尔配置中进行电子记录。荧光MERKEL细胞的平均静息膜电位为-54.0 mV，大于非荧光表皮细胞的-26.1 mV。在外标溶液中，Merkel细胞没有出现Na+峰，但在含有Ba2+和gt；的外液中注入恒流去极化可诱发出河豚毒素抗性的长时间动作电位。在电压钳下的Merkel细胞中，保持电位(V_H)为-80 mV的去极化阶跃脉冲引起的外向K~+电流主要由暂时性和持续性两部分组成：前者被4-氨基吡啶(4-AP)选择性地抑制，后者被选择性地抑制。被四乙基铵(TEA)和Qu…抑制更多的无底洞。当V^H为-50 mV时，持续外向钾电流(I&lt；Kd&gt；)在电压大于-20或-10 mV时被激活，此时瞬间外向钾通道完全失活。在V_H为-80 mV时，瞬时外向钾电流(I_A)在电压大于-50 mV时被激活。当同时加入TEA和4-AP阻断外向K~(++)电流时，仅观察到持续的内向电流。在含有10 mM-Ca^&lt；2+&gt；的外液中，当V^H为-80 mV时，I&lt；Ca&gt；可被大于-20 mV的电位诱发，最大内向电流出现在+10 mV左右。外源Ca~(2+)浓度的增加引起I_t；Ca&gt；的双曲线增加。钙通道对二价阳离子的选择性顺序为：Ba^&lt；2+&gt；&gt；sr^&lt；2+&gt；&gt；结果表明，MERKEL细胞至少存在三种不同的电压门控电流：延迟K^+电流(I&lt；Kd&gt；)、瞬时A电流(I_A)和高阈值(L型)钙电流(I&lt；Ca&gt；)。较少

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