Fraction of the dark current carried by Ca(2+) through cGMP-gated ion channels of intact rod and cone photoreceptors.
Fraction of the dark current carried by Ca(2+) through cGMP-gated ion channels of intact rod and cone photoreceptors.
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DOI：
10.1085/jgp.116.6.735
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发表时间：
2000-12
期刊：
影响因子：
--
通讯作者：
Korenbrot JI
中科院分区：
文献类型：
--
作者：
Ohyama T;Hackos DH;Frings S;Hagen V;Kaupp UB;Korenbrot JI
在视网膜视锥感受器的cGMP门控(CNG)离子通道上，钙离子对Na+的选择性(PCA/PNA)高于视杆细胞。为了确定这一事实的生理意义，我们测定了完整的视杆细胞和视锥细胞中由钙离子特异性携带的环核苷酸门控电流的比例。我们通过突然(<；5ms)在装有环核苷酸的笼酯的杆或锥的细胞质中增加游离的8BR-cGMP来激活CNG通道。同时，我们测量了细胞内钙离子结合染料Fura-2的膜电流和荧光的环核苷酸依赖性变化。在一组有限的实验条件下，Fura-2荧光变化与膜电流积分的比率是对部分钙离子通量的直接测量。在正常生理盐浓度下，不同种类的球果(或球茎)的CNG通道的分数钙离子通量高于球茎，但不同种类的球果(或球茎)之间的分数钙通量差异不大。在正常生理条件下，在膜电流≤为200pA的条件下，单锥体的钙离子分数通量为33±2%，斑点叉尾鱼为34±6%。在可比条件下，虎鳗杆状外节的Ca~(2+)分数通量为21±1%，叉尾鱼杆状外节为14±1%。随着细胞外钙离子浓度的升高，部分钙离子通量也随之增加，这种依赖关系可用Michaelis-Menten方程来描述。Ca~(2+)分数通量为50%的Kca浓度在梭鱼球果中为1.98 mM，在虎鳗鱼杆中为4.96 mM。由于锥体中的钙离子分数通量比杆状细胞中的高，所以产生相同光电流的光闪光将导致锥体中细胞质钙离子的变化大于杆状细胞中的变化。
The selectivity for Ca2+ over Na+, PCa/PNa, is higher in cGMP-gated (CNG) ion channels of retinal cone photoreceptors than in those of rods. To ascertain the physiological significance of this fact, we determined the fraction of the cyclic nucleotide–gated current specifically carried by Ca2+ in intact rods and cones. We activated CNG channels by suddenly (<5 ms) increasing free 8Br-cGMP in the cytoplasm of rods or cones loaded with a caged ester of the cyclic nucleotide. Simultaneous with the uncaging flash, we measured the cyclic nucleotide–dependent changes in membrane current and fluorescence of the Ca2+-binding dye, Fura-2, also loaded into the cells. The ratio of changes in fura-2 fluorescence and the integral of the membrane current, under a restricted set of experimental conditions, is a direct measure of the fractional Ca2+ flux. Under normal physiological salt concentrations, the fractional Ca2+ flux is higher in CNG channels of cones than in those of rods, but it differs little among cones (or rods) of different species. Under normal physiological conditions and for membrane currents ≤200 pA, the Ca2+ fractional flux in single cones of striped bass was 33 ± 2%, and 34 ± 6% in catfish cones. Under comparable conditions, the Ca2+ fractional flux in rod outer segments of tiger salamander was 21 ± 1%, and 14 ± 1% in catfish rods. Fractional Ca2+ flux increases as extracellular Ca2+ rises, with a dependence well described by the Michaelis-Menten equation. KCa, the concentration at which Ca2+ fractional flux is 50% was 1.98 mM in bass cones and 4.96 mM in tiger salamander rods. Because Ca2+ fractional flux is higher in cones than in rods, light flashes that generate equal photocurrents will cause a larger change in cytoplasmic Ca2+ in cones than in rods.
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影响因子：
3.8
作者：
BARNES, S;HILLE, B
通讯作者：
HILLE, B
DOI：
10.1085/jgp.90.4.527
发表时间：
1987-10
期刊：
The Journal of general physiology
影响因子：
--
作者：
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通讯作者：
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影响因子：
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作者：
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通讯作者：
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影响因子：
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作者：
Hackos, DH;Korenbrot, JI
通讯作者：
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影响因子：
5.5
作者：
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通讯作者：
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