Vinogradova Irina, Cook Alan, Holden-Dye Lindy
Neurosciences Research Group, School of Biological Sciences, Bassett Crescent East, University of Southampton, Southampton SO16 7PX, UK.
Invert Neurosci. 2006 Jun;6(2):57-68. doi: 10.1007/s10158-006-0018-y. Epub 2006 Apr 19.
The pharynx of Caenorhabditis elegans consists of a syncytium of radially orientated muscle cells that contract synchronously and rhythmically to ingest and crush bacteria and pump them into the intestine of the animal. The action potentials that support this activity are superficially similar to vertebrate cardiac action potentials in appearance with a long, calcium-dependent plateau phase. Although the pharyngeal muscle can generate action potentials in the absence of external calcium ions, action potentials are absent when sodium is removed from the extracellullar solution (Franks et al. 2002). Here we have used whole cell patch clamp recordings from the pharynx and show low voltage-activated inward currents that are present in zero external calcium and reduced in zero external sodium ions. Whilst the lack of effect of zero calcium when sodium ions are present is not surprising in view of the known permeability of voltage-gated calcium channels to sodium ions, the reduction in current in zero sodium when calcium ions are present is harder to explain in terms of a conventional voltage-gated calcium channel. Inward currents were also recorded from egl-19 (n582) which has a loss of function mutation in the pharyngeal L-type calcium channel and these were also markedly reduced in zero external sodium. Despite this apparent dependence on external sodium ions, the current was partially blocked by the divalent cations, cadmium, barium and nickel. Using single-channel recordings we identified a cation channel for which the open-time duration was increased by depolarisation. In inside-out patches, the single-channel conductance was highest in symmetrical sodium solution. Further studies are required to determine the contribution of these channels to the pharyngeal action potential.
秀丽隐杆线虫的咽部由呈放射状排列的肌细胞的合体细胞组成，这些肌细胞同步且有节奏地收缩，以摄取和碾碎细菌，并将它们泵入动物的肠道。支持这种活动的动作电位在外观上与脊椎动物的心脏动作电位表面相似，具有长的、钙依赖性的平台期。尽管咽部肌肉在没有外部钙离子的情况下也能产生动作电位，但当从细胞外溶液中去除钠离子时，动作电位就会消失（弗兰克斯等人，2002年）。在这里，我们使用了从咽部进行的全细胞膜片钳记录，结果显示存在低电压激活的内向电流，这些电流在外部钙离子为零时存在，而在外部钠离子为零时减少。鉴于电压门控钙通道对钠离子已知的通透性，当存在钠离子时零钙离子缺乏影响并不奇怪，但当存在钙离子时零钠离子时电流减少，用传统的电压门控钙通道很难解释。在咽部L型钙通道功能丧失突变的egl-19（n582）中也记录到了内向电流，并且在外部钠离子为零时这些电流也明显减少。尽管这种电流明显依赖于外部钠离子，但它被二价阳离子镉、钡和镍部分阻断。通过单通道记录，我们鉴定出一种阳离子通道，其开放时间持续时间因去极化而增加。在膜外翻片中，单通道电导在对称的钠溶液中最高。需要进一步的研究来确定这些通道对咽部动作电位的贡献。
