Paxilline inhibition of the alpha-subunit of the high-conductance calcium-activated potassium channel
Paxilline inhibition of the alpha-subunit of the high-conductance calcium-activated potassium channel
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DOI：
10.1016/0028-3908(96)00137-2
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发表时间：
1996-07-01
影响因子：
4.7
通讯作者：
McManus, OB
中科院分区：
文献类型：
--
作者：
Sanchez, M;McManus, OB
高电导钙激活(MAXI-K)通道被包括帕西林在内的一系列吲哚二萜有效地阻断。在电生理学实验中，帕西林可刺激轮状毒素(ChTX)与血管平滑肌最大通道的结合并阻断这些通道(Knaus ct等，1994b)。这些结果表明，Paxilline在一个不同于ChTX结合部位的位置阻断了Maxi-g通道，该部位位于毛孔外部入口附近。在这里，我们研究了在切除的膜片中，在内部应用paxilline后，最大通道的克隆的阿尔法亚单位(SLO)的阻断。帕罗西林以缓慢的洗脱动力学对通道电流产生可逆抑制。当细胞内钙离子浓度为10mU/L时，Paxilline可阻断K-I为1.9 nM、Hill系数接近1的短电压脉冲电流。当钙离子浓度增加10倍时，麻黄碱钙离子阻滞剂的K-I值变化2~3倍，钙离子浓度越高，阻滞率越低。帕罗西林以钙敏感的方式降低电导-电压关系的最大值，在高钙浓度下出现较少的阻断，并使通道开放的中点发生20 mV的去极化漂移。钙升高解除帕西林阻滞的时间进程快于帕西林的洗脱，提示钙与帕西林之间存在变构相互作用。版权所有(C)1996爱思唯尔科学有限公司
High conductance calcium-activated (maxi-K) channels are potently blocked by a family of indole diterpenes that includes paxilline. Paxilline stimulates binding of charybdotoxin (ChTX) to maxi-g channels in vascular smooth muscle and blocks these channels in electrophysiological experiments (Knaus ct al., 1994b). These results suggested that paxilline blocked maxi-g channels at a site distinct from the ChTX binding site located near the external entrance to the pore. Here we have examined block of the cloned alpha subunit (slo) of the maxi-g channel in excised membrane patches after internal application of paxilline. Paxilline caused a reversible inhibition of channel currents with slow washout kinetics. In the presence of 10 mu M intracellular calcium, paxilline blocked currents elicited by brief voltage pulses with a K-i of 1.9 nM and a Hill coefficient near one. Changing the internal calcium by ten fold caused a two to three fold change in the K-i for paxilline block, with less block occurring at high calcium concentrations. Paxilline reduced the maximum of the conductance-voltage relation in a calcium-sensitive manner with less block occurring at high calcium concentrations, and caused a 20 mV depolarizing shift in the midpoint for channel opening. The time-course of relief of paxilline block by elevated calcium was more rapid than washout of paxilline suggesting an allosteric interaction between calcium and paxilline. Copyright (C) 1996 Elsevier Science Ltd