Venglarik C J, Schultz B D, Frizzell R A, Bridges R J
Department of Physiology and Biophysics, University of Alabama at Birmingham 35294-0005.
J Gen Physiol. 1994 Jul;104(1):123-46. doi: 10.1085/jgp.104.1.123.
The cystic fibrosis gene product cystic fibrosis transmembrane conductance regulator (CFTR) is a low conductance, cAMP-regulated Cl- channel. Removal of cytosolic ATP causes a cessation of cAMP-dependent kinase-phosphorylated CFTR channel activity that resumes upon ATP addition. (Anderson, M. P., H. A. Berger, D. R. Rich, R. J. Gregory, A. E. Smith, and M. J. Welsh. 1991. Cell. 67:775-784). The aim of this study was to quantify possible effects of ATP on CFTR gating. We analyzed multichannel records since only 1 of 64 patches contained a single channel. ATP increased the channel open probability (Po) as a simple Michaelis-Menten function of concentration; the effect was half maximal at 24 microM, reached a maximum of 0.44, and had a Hill coefficient of 1.13. Since the maximum Po was not 1, the simplest description of the effect of ATP on CFTR gating is the noncooperative three-state mechanism of del Castillo and Katz (1957. Proceedings of the Royal Society of London. B. 146:369-381). We analyzed current fluctuations to quantify possible changes in CFTR gating. The power density spectra appeared to contain a single Lorentzian in the range of 0.096-31 Hz. Analysis of the corner frequency (fc) of this Lorentzian revealed that ATP increased 2 pi fc as a Michaelis-Menten function with a Hill coefficient of 1.08, and it provided estimates of the ATP dissociation constant (44 tau open (154 ms), and the ATP-sensitive tau close [(185 ms) (44 microM/[ATP] + 1)]. These results suggest that the binding reaction is rapid compared to the opening and closing rates. Assuming that there is a single set of closed-to-open transitions, it is possible to verify the outcome of fluctuation analysis by comparing fluctuation-derived estimates of Po with measures of Po from current records. The two values were nearly identical. Thus, noise analysis provides a quantitative description of the effect of ATP on CFTR opening. The noncooperative three-state model should serve as a basis to understand possible alterations in CFTR gating resulting from regulators or point mutations.
囊性纤维化基因产物囊性纤维化跨膜传导调节因子（CFTR）是一种低电导、受环磷酸腺苷（cAMP）调节的氯离子通道。去除胞质中的三磷酸腺苷（ATP）会导致依赖cAMP的蛋白激酶磷酸化的CFTR通道活性停止，而添加ATP后活性恢复。（安德森，M.P.，H.A.伯杰，D.R.里奇，R.J.格雷戈里，A.E.史密斯，和M.J.威尔士。1991年。《细胞》。67:775 - 784）。本研究的目的是量化ATP对CFTR门控的可能影响。我们分析了多通道记录，因为64个膜片中只有1个包含单通道。ATP以简单的米氏函数增加通道开放概率（Po）；该效应在24微摩尔时达到半数最大效应，最大值为0.44，希尔系数为1.13。由于最大Po不是1，对ATP对CFTR门控影响的最简单描述是德尔卡斯蒂略和卡茨（1957年。《伦敦皇家学会学报》。B.146:369 - 381）的非协同三态机制。我们分析了电流波动以量化CFTR门控的可能变化。功率密度谱在0.096 - 31赫兹范围内似乎包含一个单一的洛伦兹曲线。对该洛伦兹曲线的转折频率（fc）分析表明，ATP以米氏函数增加2πfc，希尔系数为1.08，并提供了ATP解离常数的估计值（44τ开放（154毫秒），以及ATP敏感的τ关闭[（185毫秒）（44微摩尔/[ATP] + 1）]。这些结果表明，与开放和关闭速率相比，结合反应很快。假设存在一组单一的从关闭到开放的转变，通过将波动推导的Po估计值与电流记录中的Po测量值进行比较，可以验证波动分析的结果。这两个值几乎相同。因此，噪声分析提供了ATP对CFTR开放影响的定量描述。非协同三态模型应作为理解调节因子或点突变导致的CFTR门控可能改变的基础。
