Heterologous expression of BI Ca2+ channels in dysgenic skeletal muscle.
Heterologous expression of BI Ca2+ channels in dysgenic skeletal muscle.
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BI Ca2 通道在发育不良骨骼肌中的异源表达。
DOI：
10.1085/jgp.104.5.985
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发表时间：
1994
期刊：
影响因子：
--
通讯作者：
Beam,KG
中科院分区：
文献类型：
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作者：
Adams,BA;Mori,Y;Kim,MS;Tanabe,T;Beam,KG
我们检查了从兔脑克隆的BI（A类）Ca 2+通道介导骨骼肌兴奋-收缩（E-C）偶联的能力。将携带编码BI通道的cDNA的表达质粒显微注射到在原代培养物中生长的发育不良小鼠肌管的细胞核中。采用全细胞膜片钳技术记录BI通道产生的离子电流和膜内电荷运动。注射的肌管表达高密度的离子BI Ca 2+通道电流（平均31 pA/pF），但没有显示自发收缩，只有很少显示诱发收缩。表达的离子电流通过其对二氢吡啶拮抗剂（+）-PN 200-110的不敏感性而与发育不良骨骼肌（Idys）的内源性L型电流明显区别。峰值BI Ca 2+电流以约2 ms的时间常数（tau a）激活，并以约260 ms的时间常数（tau h）失活（20-23 ℃）。失活的时间常数（τ h）没有增加，通过取代Ba 2+作为电荷载体的Ca 2+，表明在发育不良的肌管中表达的BI通道不经历Ca（2+）依赖性失活。BI通道产生的平均最大Ca 2+电导（Gmax）相当大（约534 S/F）。相比之下，在相同的肌管中产生的平均最大电荷移动（Qmax）（约2.7 nC/microF）相当小，几乎不大于对照发育不良肌管中的Qmax（约2.3 nC/microF）。因此，BI通道的Gmax/Qmax比先前在相同系统中表达的心肌或骨骼肌L型Ca 2+通道中发现的高得多，表明神经元BI Ca 2+通道表现出比这些L型Ca 2+通道高得多的开放概率。
We have examined the ability of BI (class A) Ca2+ channels, cloned from rabbit brain, to mediate excitation-contraction (E-C) coupling in skeletal muscle. Expression plasmids carrying cDNA encoding BI channels were microinjected into the nuclei of dysgenic mouse myotubes grown in primary culture. Ionic currents and intramembrane charge movements produced by the BI channels were recorded using the whole-cell patch-clamp technique. Injected myotubes expressed high densities of ionic BI Ca2+ channel current (average 31 pA/pF) but did not display spontaneous contractions, and only very rarely displayed evoked contractions. The expressed ionic current was pharmacologically distinguished from the endogenous L-type current of dysgenic skeletal muscle (Idys) by its insensitivity to the dihydropyridine antagonist (+)-PN 200-110. Peak BI Ca2+ currents activated with a time constant (tau a) of approximately 2 ms and inactivated with a time constant (tau h) of approximately 260 ms (20-23 degrees C). The time constant of inactivation (tau h) was not increased by substituting Ba2+ for Ca2+ as charge carrier, demonstrating that BI channels expressed in dysgenic myotubes do not undergo Ca(2+)-dependent inactivation. The average maximal Ca2+ conductance (Gmax) produced by the BI channels was quite large (approximately 534 S/F). In contrast, the average maximal charge movement (Qmax) produced in the same myotubes (approximately 2.7 nC/microF) was quite small, being barely larger than Qmax in control dysgenic myotubes (approximately 2.3 nC/microF). Thus, the ratio Gmax/Qmax for the BI channels was considerably higher than previously found for cardiac or skeletal muscle L-type Ca2+ channels expressed in the same system, indicating that neuronal BI Ca2+ channels exhibit a much higher open probability than these L-type Ca2+ channels.