Permeant ion binding affinity in subconductance states of an L-type Ca2+ channel expressed in Xenopus laevis oocytes.
Permeant ion binding affinity in subconductance states of an L-type Ca2+ channel expressed in Xenopus laevis oocytes.
复制标题
非洲爪蟾卵母细胞中表达的 L 型 Ca2 通道亚电导状态下的渗透离子结合亲和力。
DOI：
10.1111/j.1469-7793.2000.00019.x
复制
发表时间：
2000
期刊：
影响因子：
--
通讯作者：
Sather,WA
中科院分区：
文献类型：
--
作者：
Cloues,RK;Sather,WA
1The relationship between single‐channel conductance and ion binding affinity in Ca2+channels was investigated by measuring differences in the apparent binding affinity (K′D) for Ca2+among naturally occurring conductance states of an L‐type (α1C) Ca2+channel heterologously expressed inXenopusoocytes. Using cell‐attached patch recordings, three or more conductance levels were observed when Ca2+, Ba2+or Li+was used as the permeating ion.2With Li+as the charge carrier, low concentrations of Ca2+(0.1‐3.0 μM) produced discrete blocking events in all conductance states. Measurements of open and blocked times as a function of Ca2+concentration were used to calculate rates of block and unblock.3K′Dwas calculated for three of the conductance levels. Binding affinity for Ca2+increased as conductance decreased (K′D: large = 7.5 μM, medium = 4.0 μM, small = 2.7 μM). The lowerK′Dvalues of the smaller conductance states arose from a combination of larger on‐rates and smaller off‐rates.4These results imply that permeant ions such as Ca2+have both easier access to, and longer dwell time in, the Ca2+binding locus in the pore when the channel opens to a subconductance level as compared to the fully open level.5The difference inK'Dbetween the large and small conductance levels corresponds to a small difference in the free energy of binding, ΔΔG≈ 1kBT, wherekBis Boltzmann's constant andTis absolute temperature (kelvin). Nonetheless, an Eyring model of Ca2+channel permeation incorporating the state‐specific on‐ and off‐rate constants for Ca2+was able to reproduce the large difference in channel conductance, indicating that small differences in binding energy may be able to account for large differences in amplitude between conductance states.
