Wu C F, Haugland F N
J Neurosci. 1985 Oct;5(10):2626-40. doi: 10.1523/JNEUROSCI.05-10-02626.1985.
The body wall muscles in Drosophila larvae are suitable for voltage clamp analysis of changes in membrane excitability caused by mutations. Both inward and outward ionic currents are present in these muscle fibers. The inward current is mediated by voltage-dependent Ca2+ channels. In Ca2+-free saline, the inward current is eliminated. The remaining outward K+ currents consist of two distinct components, an early transient IA and a delayed steady IK, which are separable by differences in the rate and voltage dependence of activation and inactivation. The steady-state and kinetic properties of the activation and inactivation processes of these two currents are analyzed. The results provide a basis for quantitative analysis of altered membrane currents in behavioral mutants of Drosophila. Previous studies indicate that mutations in the Shaker (Sh) locus alter excitability in both nerve and muscle in Drosophila. Our results support the idea that the channels mediating IA are molecularly distinct from those mediating IK. All Sh mutations studied specifically affect IA without changing the properties of the calcium current and IK. In certain alleles (ShKS133, Sh102, and ShM) IA is eliminated, permitting detailed studies of IK in isolation of IA. Studies of the alleles that do not eliminate IA provide additional information of the channels. In one such allele, Sh5, voltage dependence of IA activation is shifted to more positive potentials. This is accompanied by a less pronounced shift in the voltage dependence of inactivation. These results suggest that Sh5 mutation affects the voltage-sensitive mechanism of both activation and inactivation processes and that these two processes are not controlled by independent parts of the channel. Furthermore, the differential effects of these alleles on different excitable membranes imply that other genes take part in the control of IA. The effects of Sh5 on muscle depend on developmental stage. In larval muscle, Sh5 reduces the amplitude of IA because of the shift in the current-voltage (I-V) relation. In contrast, in adult Sh5 muscles, IA is reported to be normal in amplitude but shows abnormally rapid inactivation (Salkoff, L., and R. Wyman (1981) Nature 293: 228-230). A different allele, ShrK0120, causes a clear defect in nerve excitability, but analysis of IA in ShrK0120 larval muscle reveals I-V relations, inactivation, and recovery from inactivation similar to those seen in normal fibers. We suggest a possible mechanism of combinations of multiple interacting genes participating in the control of potassium channels to account for the presence of a variety of potassium channels in different excitable membranes.
果蝇幼虫的体壁肌肉适合用于对由突变引起的膜兴奋性变化进行电压钳分析。这些肌肉纤维中存在内向和外向离子电流。内向电流由电压依赖性Ca2+通道介导。在无Ca2+的盐溶液中，内向电流消失。剩余的外向K+电流由两个不同的成分组成，一个早期瞬态IA和一个延迟稳态IK，它们可通过激活和失活的速率及电压依赖性差异来分离。分析了这两种电流的激活和失活过程的稳态和动力学特性。这些结果为定量分析果蝇行为突变体中膜电流的改变提供了基础。先前的研究表明，震颤（Sh）基因座的突变会改变果蝇神经和肌肉的兴奋性。我们的结果支持这样的观点，即介导IA的通道在分子水平上与介导IK的通道不同。所研究的所有Sh突变都特异性地影响IA，而不改变钙电流和IK的特性。在某些等位基因（ShKS133、Sh102和ShM）中，IA消失，从而可以在分离IA的情况下详细研究IK。对未消除IA的等位基因的研究提供了关于通道的更多信息。在一个这样的等位基因Sh5中，IA激活的电压依赖性向更正的电位偏移。这伴随着失活电压依赖性的不太明显的偏移。这些结果表明，Sh5突变影响激活和失活过程的电压敏感机制，并且这两个过程不受通道独立部分的控制。此外，这些等位基因对不同可兴奋膜的不同影响意味着其他基因参与了IA的控制。Sh5对肌肉的影响取决于发育阶段。在幼虫肌肉中，由于电流-电压（I-V）关系的偏移，Sh5降低了IA的幅度。相反，在成年Sh5肌肉中，据报道IA的幅度正常，但显示出异常快速的失活（索尔科夫，L.，和R·怀曼（1981年）《自然》293：228 - 230）。另一个等位基因ShrK0120在神经兴奋性方面导致明显缺陷，但对ShrK0120幼虫肌肉中IA的分析揭示了与正常纤维中相似的I-V关系、失活和从失活中恢复的情况。我们提出了一种多个相互作用基因组合参与钾通道控制的可能机制，以解释在不同可兴奋膜中存在多种钾通道的现象。
