Effect of changing temperature on the ionic permeation through the cyclic GMP-gated channel from vertebrate photoreceptors
Effect of changing temperature on the ionic permeation through the cyclic GMP-gated channel from vertebrate photoreceptors
复制标题
DOI：
10.1016/s0006-3495(96)79832-6
复制
发表时间：
1996-06-01
影响因子：
3.4
通讯作者：
Torre, V
中科院分区：
文献类型：
--
作者：
Sesti, F;Nizzari, M;Torre, V
本文研究了虎纹腹水蚤杆状外节的天然cGMP门控通道。牛cGMP门控通道的α亚基在非洲爪哇卵母细胞中异源表达，这里称为野生型(W.T.)和突变型通道。在由内向外结构的离体膜贴片中研究这些通道，并通过添加100或500亩M cGMP来激活这些通道。研究了温度对离子渗透的影响。在+100 mV下，Li+、Na+、K+、Rb+、Cs+和NH4+的激活能分别为35.8、30、31.8、34.5、41.3和22.4kJ mol(-1)。流经W.T.的宏观水流。在+100 mV时，Li+、Na+、K+、Rb+、Cs+和NH4+的激活能分别为45.2、38.2、37.5、47.3、49.4和38.9kJ mol(-1)。宏观电流的激活能流经自然和W.T。当离子浓度在2.5-110 mM之间变化时，通道没有显著变化。W.T的单通道电流的激活能。在+100 mV下，Na+和NH4+的通道分别为40.4和33kJ mol(-1)，双离子溶液的反转电位随温度的变化而显著变化。这些结果可以用来估计离子在穿过明渠时所经历的吉布斯自由能势垒的焓和熵的贡献。这些估计表明，cGMP门控通道的离子渗透和选择性既受焓因素的控制，也受熵因素的控制，而天然通道对Li+的选择性主要是由熵效应引起的。
Native cGMP-gated channels were studied in rod outer segments of the lawal tiger salamander Ambystoma tigrinum. The a subunit of the cGMP-gated channel from bovine rods, here referred to as the wild type (w.t.), and mutant channels were heterologously expressed in Xenopus laevis oocytes. These channels were studied in excised membrane patches in the inside-out configuration and were activated by the addition of 100 or 500 mu M cGMP. The effect of temperature on the ionic permeation was studied. The macroscopic current flowing through the native channel at +100 mV had an activation energy of 35.8, 30, 31.8, 34.5, 41.3, and 22.4 kJ mol(-1) in the presence of Li+, Na+, K+, Rb+, Cs+, and NH4+ respectively. The macroscopic current flowing through the w.t. channel at +100 mV had an activation energy of 45.2, 38.2, 37.5, 47.3, 49.4, and 38.9 kJ mol(-1) in the presence of Li+, Na+, K+, Rb+, Cs+, and NH4+ respectively. The activation energy of the macroscopic current flowing through the native and w.t. channels did not vary significantly when the ionic concentration of the permeant ion was changed between 2.5 and 110 mM. The activation energy of the single-channel current of the w.t. channel at +100 mV was 40.4 and 33 kJ mol(-1) for Na+ and NH4+, respectively, The reversal potential of biionic solutions changed significantly with temperature. These results can be used to obtain an estimate of the enthalpic and entropic contributions to the barrier of the Gibbs free energy experienced by an ion during its permeation through the open channel. These estimates indicate that the ionic permeation and selectivity of the cGMP-gated channel are controlled both by enthalpic and entropic factors and that the selectivity of the native channel for Li+ over Nai is primarily caused by entropic effects.