Walther C, Zittlau K E
Physiological Institute, Neuroendocrinology Working Group, University of Marburg, 35037 Marburg, Germany.
J Neurophysiol. 1998 Aug;80(2):785-97. doi: 10.1152/jn.1998.80.2.785.
Ionic currents in the resting membrane of locust jumping muscle and their modulation by the biogenic amine octopamine were investigated using the two-electrode voltage clamp. A Cl- conductance, GCl,H, which slowly activates on hyperpolarization, can be induced by raising the intracellular Cl- concentration via diffusion of Cl- ions from the recording electrode. The instantaneous I-V characteristic of the current, ICl,H, is linear and reverses at the same potential as the gamma-aminobutyric acid (GABA)-mediated Cl- current. Elevation of [Cl-]i increases the maximal steady state GCl,H (Gmax) and shifts the activation curve of GCl,H to more positive potentials. Octopamine enhances GCl,H, mainly by increasing Gmax. Octopamine also lowers the resting K+ conductance (GK,r). It reduces a hyperpolarization-activated component (GK,H) of GK,r, mainly by decreasing Gmax. Octopamine also transiently stimulates the Na+/K+ pump although this effect was not always seen. The effects of octopamine on the Cl- and K+ conductances are mimicked by membrane permeant cyclic nucleotides. The modulation of GK,r, but not that of GCl,H, seems to be mediated by protein kinase A (PKA). PKA seems to be constitutively activated as indicated by the pronounced increase in GK,r induced by a PKA inhibitor, H89. The properties of GCl,H and related Cl- conductances in invertebrate and vertebrate neurons are compared. GCl,H probably supports efflux of Cl- ions accumulating in the fibers during synaptic inhibition. Octopamine's multiple modulation at the level of the muscle cell membrane, in conjunction with previously established effects on synaptic transmission and excitation-contraction coupling, are suited to support strong and rapid muscle contractions.
利用双电极电压钳研究了蝗虫跳跃肌静息膜中的离子电流及其受生物胺章鱼胺的调节。一种Cl-电导GCl,H，在超极化时缓慢激活，可通过Cl-离子从记录电极扩散来提高细胞内Cl-浓度而诱导产生。电流ICl,H的瞬时I-V特性是线性的，且在与γ-氨基丁酸（GABA）介导的Cl-电流相同的电位处反转。[Cl-]i升高会增加最大稳态GCl,H（Gmax），并将GCl,H的激活曲线向更正的电位移动。章鱼胺主要通过增加Gmax来增强GCl,H。章鱼胺还降低静息K+电导（GK,r）。它主要通过降低Gmax来减少GK,r中超极化激活成分（GK,H）。章鱼胺还会短暂刺激Na+/K+泵，尽管这种效应并非总能观察到。膜通透性环核苷酸可模拟章鱼胺对Cl-和K+电导的影响。GK,r的调节似乎由蛋白激酶A（PKA）介导，而GCl,H的调节并非如此。如PKA抑制剂H89诱导的GK,r显著增加所示，PKA似乎持续被激活。比较了无脊椎动物和脊椎动物神经元中GCl,H及相关Cl-电导的特性。GCl,H可能支持在突触抑制期间纤维中积累的Cl-离子外流。章鱼胺在肌细胞膜水平的多重调节，与先前确定的对突触传递和兴奋收缩偶联的影响相结合，适合支持强烈而快速的肌肉收缩。
