Wangemann P, Takeuchi S
Cell Physiology Laboratory, Boystown National Research Hospital, Omaha, NE 68131.
Hear Res. 1993 Apr;66(2):123-9. doi: 10.1016/0378-5955(93)90133-l.
Patch clamp recordings were obtained from isolated cochlear efferent nerve terminals. Channel activity was found in 85% of membrane patches, was present in on-terminal and excised patches and was characterized to originate from a maxi-K+ channel. An average of 2.0 +/- 0.1 (N = 33) maxi-K+ channels were found per active patch. In symmetrical solutions, the current-voltage relationship was linear and the single-channel conductance was 221 +/- 5 pS (N = 22). The open probability of the maxi-K+ channel increased with depolarization of the membrane potential and with an increasing free Ca2+ concentration on the cytosolic side. The open probability was insensitive to changes in the free Ca2+ concentration on the extracellular side. TEA (20 mM) and charybdotoxin (10(-7) M) decreased the open probability to nearly zero from the extracellular side but had no effect from the cytosolic side. The high incidence with which this channel was found suggests that the maxi-K+ channel is physiologically relevant which might include protection against overstimulation of the efferent synapse.
从分离出的耳蜗传出神经末梢进行膜片钳记录。在85%的膜片中发现有通道活性，其存在于终末膜片和切除的膜片中，并且其特征是起源于大电导钾通道。每个活性膜片平均发现2.0±0.1个（N = 33）大电导钾通道。在对称溶液中，电流-电压关系呈线性，单通道电导为221±5 pS（N = 22）。大电导钾通道的开放概率随着膜电位的去极化以及胞质侧游离钙离子浓度的增加而增加。开放概率对细胞外侧游离钙离子浓度的变化不敏感。从细胞外侧加入20 mM四乙铵（TEA）和10⁻⁷ M蝎毒素可使开放概率降至几乎为零，但从胞质侧加入则无影响。发现该通道的高发生率表明大电导钾通道具有生理相关性，这可能包括防止传出突触过度刺激。
