鸭嘴兽（Ornithorhynchus anatinus）毒液的一种成分会形成动力学缓慢的阳离子通道。

A component of platypus (Ornithorhynchus anatinus) venom forms slow-kinetic cation channels.

作者信息

Kourie J I

机构信息

Membrane Transport Group, Department of Chemistry, The Faculties, The Australian National University, Canberra City, ACT, 0200 Australia.

出版信息

J Membr Biol. 1999 Nov 1;172(1):37-45. doi: 10.1007/s002329900581.

DOI:10.1007/s002329900581

PMID:10552012

Abstract

The lipid bilayer technique is used to examine the biophysical properties of anion and cation channels frequently formed by platypus (Ornithorhynchus anatinus) venom (OaV). The OaV-formed anion channel in 250/50 mm KCl cis/trans has a maximum conductance of 857 +/- 23 pS (n = 5) in 250/50 mm KCl cis/trans. The current-voltage relationship of this channel shows strong inward rectification. The channel activity undergoes time-dependent inactivation that can be removed by depolarizing voltage steps more positive than the reversal potential for chloride, E(Cl), (+40 mV). The reversal potential of the OaV-formed slow current activity in 250/50 mm KCl cis/trans is close to the potassium equilibrium potential (E(K)) of -40 mV. The conductance values for the slow channel are 22.5 +/- 2.6 pS and 41.38 +/- 4.2 pS in 250/50 and 750/50 mm cis/trans, respectively. The gating kinetics of the slow ion channels are voltage-dependent. The channel open probability (P(o)) is between 0.1 and 0.8 at potentials between 0 and +140 mV. The channel frequency (F(o)) increases with depolarizing voltages between 0 and +140 mV, whereas mean open time (T(o)) and mean closed time (T(c)) decrease. Ion substitution experiments of the cis solution show that the channel has conductance values of 21.47 +/- 2. 3 and 0.53 +/- 0.1 pS in 250 mm KCl and choline Cl, respectively. The amplitude of the single channel current is dependent on K(+) and the current reversal potential (E(rev)) responds to increases in K(+) by shifting to more negative voltages. The increase in current amplitude as a function of increasing K(+) can be best described by a third order polynomial fit. At +140 mV, the values of the maximal single channel conductance (gamma(max)) and the concentration for half maximal gamma (K(s)) are 38.6 pS and 380 mm and decline to 15.76 pS and 250 mm at 0 mV, respectively. The ion selectivity of the channel to K(+), Na(+), Cs(+) and choline(+) was determined in ion substitution experiments. The permeability values for P(K(+)):P(Na(+)):P(Cs(+)):P(choline(+)) were 1:1:0.63:0.089, respectively. On the other hand, the activity of the slow channel was eliminated (Fig. 7B). The slow channel was reversibly inhibited by TEA(+) and the half-maximal inhibitory concentration (K(i)) was approximately 48 mm.

摘要

脂质双层技术用于检测由鸭嘴兽（Ornithorhynchus anatinus）毒液（OaV）频繁形成的阴离子和阳离子通道的生物物理特性。在250/50 mM KCl顺式/反式条件下，由OaV形成的阴离子通道的最大电导在250/50 mM KCl顺式/反式条件下为857±23 pS（n = 5）。该通道的电流-电压关系显示出强烈的内向整流。通道活性经历时间依赖性失活，这种失活可通过比氯离子的反转电位E(Cl)（+40 mV）更正的去极化电压阶跃来消除。在250/50 mM KCl顺式/反式条件下，由OaV形成的慢电流活性的反转电位接近-40 mV的钾平衡电位（E(K)）。在250/50和750/50 mM顺式/反式条件下，慢通道的电导值分别为22.5±2.6 pS和41.38±4.2 pS。慢离子通道的门控动力学是电压依赖性的。在0至+140 mV的电位下，通道开放概率（P(o)）在0.1至0.8之间。通道频率（F(o)）随着0至+140 mV的去极化电压增加而增加，而平均开放时间（T(o)）和平均关闭时间（T(c)）减少。顺式溶液的离子置换实验表明，该通道在250 mM KCl和氯化胆碱中的电导值分别为21.47±2.3和0.53±0.1 pS。单通道电流的幅度取决于K⁺，并且电流反转电位（E(rev)）随着K⁺的增加而向更负的电压移动。电流幅度随K⁺增加的函数关系可以用三阶多项式拟合来最好地描述。在+140 mV时，最大单通道电导（γ(max)）和半最大γ浓度（K(s)）的值分别为38.6 pS和380 mM，在0 mV时分别降至15.76 pS和250 mM。在离子置换实验中确定了该通道对K⁺、Na⁺、Cs⁺和胆碱⁺的离子选择性。P(K⁺):P(Na⁺):P(Cs⁺):P(胆碱⁺)的渗透率值分别为1:1:0.63:0.089。另一方面，慢通道的活性被消除（图7B）。慢通道被TEA⁺可逆抑制，半最大抑制浓度（K(i)）约为48 mM。