Baumann Ludwig, Gerstner Andrea, Zong Xiangang, Biel Martin, Wahl-Schott Christian
Department Pharmazie, Pharmakologie für Naturwissenschaften, Ludwig-Maximilians Universität Munich, Munich, Germany.
Invest Ophthalmol Vis Sci. 2004 Feb;45(2):708-13. doi: 10.1167/iovs.03-0937.
To study the electrophysiological and pharmacological properties of the L-type Ca(2+) channel (LTCC) Ca(v)1.4alpha1 (alpha1F) subunit from mouse retina and assess their contributions to the native retinal channel.
The full-length cDNA of Ca(v)1.4alpha1 was cloned from murine retina in an RT-PCR approach. Ca(v)1.4alpha1 was expressed alone or together with the auxiliary alpha2delta1 and beta2a or beta3 subunits in HEK293 cells. The electrophysiological and pharmacological characteristics of L-type Ca(2+) and Ba(2+) inward currents (I(Ca) and I(Ba)) induced by Ca(v)1.4alpha1 were determined by the whole-cell configuration of the patch-clamp method and compared with currents induced by the cardiac and smooth muscle-type Ca(v)1.2alpha1 (alpha1C) channel.
Ca(v)1.4alpha1-mediated I(Ba) was observed only when the alpha2delta1 and beta subunits were coexpressed. Current densities were approximately two times higher with beta2a than with beta3. I(Ba) activated faster and revealed much slower time-dependent inactivation than I(Ba) induced by Ca(v)1.2alpha1. Unlike in Ca(v)1.2alpha1, inactivation was not accelerated with Ca(2+) as the charge carrier, indicating the absence of Ca(2+)-dependent inactivation in Ca(v)1.4alpha1. Ca(v)1.4alpha1 exhibited voltage-dependent inactivation. The dihydropyridine (DHP) antagonist isradipine blocked Ca(v)1.4alpha1 with approximately 20-fold lower sensitivity than Ca(v)1.2alpha1. The agonistic DHP BayK 8644 stimulated maximum I(Ba) approximately sixfold. Ca(v)1.4alpha1 revealed only moderate sensitivities to L- and D-cis-diltiazem, with IC(50) in the micromolar range. Both enantiomers unexpectedly blocked Ca(v)1.4alpha1 with almost equal IC(50).
The data indicate that Ca(v)1.4alpha1 subunit constitutes the major molecular correlate of retinal L-type Ca(2+) current. Its intrinsic biophysical properties, in particular its unique inactivation properties, enable Ca(v)1.4alpha1 to provide a sustained I(Ca) over a voltage range such as required for tonic glutamate release at the photoreceptor synapse.
研究小鼠视网膜L型钙通道（LTCC）Ca(v)1.4α1（α1F）亚基的电生理和药理学特性，并评估它们对天然视网膜通道的贡献。
采用RT-PCR方法从鼠视网膜中克隆Ca(v)1.4α1的全长cDNA。Ca(v)1.4α1单独表达或与辅助性α2δ1和β2a或β3亚基在HEK293细胞中共表达。通过膜片钳技术的全细胞模式测定Ca(v)1.4α1诱导的L型钙电流和钡电流（I(Ca)和I(Ba)）的电生理和药理学特性，并与心肌和平滑肌型Ca(v)1.2α1（α1C）通道诱导的电流进行比较。
仅当α2δ1和β亚基共表达时才观察到Ca(v)1.4α1介导的I(Ba)。β2a存在时的电流密度比β3存在时高约两倍。与Ca(v)1.2α1诱导的I(Ba)相比，I(Ba)激活更快，且显示出慢得多的时间依赖性失活。与Ca(v)1.2α1不同，以Ca(2+)作为载流子时失活并未加速，表明Ca(v)1.4α1不存在Ca(2+)依赖性失活。Ca(v)1.4α1表现出电压依赖性失活。二氢吡啶（DHP）拮抗剂伊拉地平阻断Ca(v)1.4α1的敏感性比阻断Ca(v)1.2α1低约20倍。激动性DHP BayK 8644刺激最大I(Ba)增加约6倍。Ca(v)1.4α1对L-和D-顺式地尔硫䓬仅表现出中等敏感性，IC(50)在微摩尔范围内。两种对映体意外地以几乎相等的IC(50)阻断Ca(v)1.4α1。
数据表明Ca(v)1.4α1亚基构成视网膜L型钙电流的主要分子相关物。其内在的生物物理特性，特别是其独特的失活特性，使Ca(v)1.4α1能够在一个电压范围内提供持续的I(Ca)，如光感受器突触处持续性谷氨酸释放所需要的那样。
