The actions of chloride channel blockers, barbiturates and a benzodiazepine on Caenorhabditis elegans glutamate- and ivermectin-gated chloride channel subunits expressed in Xenopus oocytes

Abstract

The pharmacology of Caenorhabditis elegans glutamate-gated chloride (GluCl) channels was determined by making intracellular voltage-clamp recordings from Xenopus oocytes expressing GluCl subunits. As previously reported (Cully et al. 1994), GluCla1b responded to glutamate (in a picrotoxin sensitive manner) and ivermectin, while GluClb responded only to glutamate and GluCla1 only to ivermectin. This assay was used to further investigate the action of chloride channel compounds. The arylaminobenzoate, NPPB, reduced the action of glutamate on the heteromeric GluCla1b channel (IC 50 6.03 ± 0.81 lM). The disulphonate stilbene, DNDS, blocked the effect of both glutamate and ivermectin on GluCla1b channels, the action of glutamate on GluClb subunits, and the effect of ivermectin on GluCla1 subunits (IC 50 s 1.58-3.83 lM). Surprisingly, amobarbital and pentobarbital, otherwise known as positive allosteric modulators of ligand-gated chloride channels, acted as antagonists. Both compounds reduced the action of glutamate on the GluCla1b heteromer (IC 50 s of 2.04 ± 0.5 and 17.56 ± 2.16 lM, respectively). Pentobarbital reduced the action of glutamate on the GluClb homomeric subunit with an IC 50 of 0.59 ± 0.09 lM, while reducing the responses to ivermectin on both GluCla1b and GluCla1 with IC 50 s of 8.7 ± 0.5 and 12.9 ± 2.5 lM, respectively. For all the antagonists, the mechanism is apparently noncompetitive. The benzodiazepine, flurazepam had no apparent effect on these glutamate-and ivermectin-gated chloride channel subunits. Thus, arylaminobenzoates, disulphonate stilbenes, and barbiturates are non-competitive antagonists of C. elegans GluCl channels.

Regenerative Adaptation to Electrochemical Perturbation in Planaria: A Molecular Analysis of Physiological Plasticity

“…NPPB (5 μM) and niflumic acid (1.25 μM) were used as calcium-activated chloride channel blockers. Both of these drugs have been shown to block Cl − channels both in mammalian cells and in C. elegans (Bush et al., 2009, Schriever et al., 1999, White and Aylwin, 1990, Wu and Hamill, 1992). NPPB delayed degeneration in most worms (82%) until day 6, at which point all worms died, suggesting only a partial rescue of the excitotoxic effect (Figures 4Ag and 4Ah).…”