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

Electrically silent mutants unravel the mechanism of binding-gating coupling in Cys-loop receptors

The transduction of extracellular chemical signals into intracellular events relies on the communication between neighboring domains of membrane receptors. In the particular case of Cys-loop receptor channels, five short stretches of amino acids, one per subunit, link the extracellular and transmembrane domains in such a way that the ion permeability of the latter and the affinity for neurotransmitters of the former become tied to each other. Here, using direct functional approaches, we set out to understand the molecular bases of this crucial interdependence through the characterization of total loss-of-current mutations at the interface between domains. Our results indicate that domain-domain proximity plays a previously unnoticed critical role inasmuch as inserting a single residue in each linker rendered the two domains independent of each other. In marked contrast, loss-of-current mutations that leave the linkers' length unaltered did not compromise the interdomain coupling, but rather, seemed to cause agonist-bound closed receptors to desensitize without appreciably opening.

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

Anatomical homeostasis results from dynamic interactions between gene expression, physiology, and the external environment. Owing to its complexity, this cellular and organism-level phenotypic plasticity is still poorly understood. We establish planarian regeneration as a model for acquired tolerance to environments that alter endogenous physiology. Exposure to barium chloride (BaCl₂) results in a rapid degeneration of anterior tissue in Dugesia japonica. Remarkably, continued exposure to fresh solution of BaCl₂ results in regeneration of heads that are insensitive to BaCl₂. RNA-seq revealed transcriptional changes in BaCl₂-adapted heads that suggests a model of adaptation to excitotoxicity. Loss-of-function experiments confirmed several predictions: blockage of chloride and calcium channels allowed heads to survive initial BaCl₂ exposure, inducing adaptation without prior exposure, whereas blockade of TRPM channels reversed adaptation. Such highly adaptive plasticity may represent an attractive target for biomedical strategies in a wide range of applications beyond its immediate relevance to excitotoxicity preconditioning.

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Exposure to BaCl₂ causes the heads of Dugesia japonica to degenerate

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Prolonged exposure to BaCl₂ results in regeneration of a BaCl₂-insensitive head

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Ion channel expression is altered in the head to compensate for excitotoxic stress

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TRPMa is upregulated in BaCl₂-treated animals; blocking TRPM prevents adaptation