Spreadbury I C, Kros C J, Meech R W
Neurosciences Group, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, UK.
Hear Res. 2004 Apr;190(1-2):115-27. doi: 10.1016/S0378-5955(03)00376-9.
High-conductance Ca(2+)-activated K(+) (BK(Ca)) channels from isolated adult guinea-pig outer hair cells were studied in inside-out membrane patches. They had a 300 pS unitary conductance and were inhibited by tetraethyl ammonium (1 mM), iberiotoxin (33 nM) and charybdotoxin (50 nM). In symmetrical 144 mM KCl their K(+) permeability (P(K)) was 5.4 x 10(-13) cm(3)/s; this was reduced to around 4.5 x 10(-13) cm(3)/s with 160 mM Na(+) in place of K(+) on either internal or external membrane surface. BK(Ca) channels from trypsin-isolated hair cells had a high open probability, that depended on both membrane voltage (16 mV/e-fold change) and the concentration of calcium ions at their intracellular surface (Ca(2+)). The Hill coefficient was 3-4. About 50% of BK(Ca) channels from mechanically isolated outer hair cells had similar characteristics; the remainder had the same high conductance but a low open probability. Trypsin (<0.5 mg/ml) applied to the intracellular face of these 'inactive' channels markedly increased their open probability. It is possible that exposure to trypsin during cell isolation removes an inactivating beta subunit. This would account for the absence of 'inactive' BK(Ca) channels in trypsin-isolated cells.
在膜片内向外模式下，对分离的成年豚鼠外毛细胞的高电导钙激活钾（BK(Ca)）通道进行了研究。它们的单通道电导为300 pS，可被四乙铵（1 mM）、iberiotoxin（33 nM）和蝎毒素（50 nM）抑制。在对称的144 mM KCl溶液中，其钾离子通透性（P(K)）为5.4×10⁻¹³ cm³/s；当内膜或外膜表面用160 mM Na⁺代替K⁺时，该通透性降至约4.5×10⁻¹³ cm³/s。胰蛋白酶分离的毛细胞中的BK(Ca)通道具有较高的开放概率，这取决于膜电压（16 mV/十倍变化）及其细胞内表面的钙离子浓度（Ca²⁺）。希尔系数为3 - 4。机械分离的外毛细胞中约50%的BK(Ca)通道具有类似的特性；其余通道具有相同的高电导，但开放概率较低。将胰蛋白酶（<0.5 mg/ml）作用于这些“无活性”通道的细胞内面，可显著增加其开放概率。细胞分离过程中暴露于胰蛋白酶可能会去除一个失活的β亚基。这可以解释为什么在胰蛋白酶分离的细胞中不存在“无活性”的BK(Ca)通道。
