Inhibition of human alpha1E subunit-mediated ca2+ channels by the antipsychotic agent chlorpromazine

Neuroleptic Chlorpromazine Modulates Ca2+ Responses in Macrophages

Using Fura-2AM microfluorimetry, we have shown for the first time that sigma-1 receptor antagonist neuroleptic chlorpromazine significantly inhibits glutoxim- and molixan-induced Ca²⁺ responses and Ca²⁺ responses induced by endoplasmic reticulum Са²⁺-ATPase inhibitors thapsigargin and cyclopiazonic acid in rat peritoneal macrophages. The results suggest the involvement of sigma-1 receptors in the signaling cascade induced by glutoxim or molixan and leading to intracellular Ca²⁺ concentration increase and in the regulation of store-dependent Ca²⁺ entry in macrophages.

Octopamine signaling in the metazoan pathogen Schistosoma mansoni: localization, small-molecule screening and opportunities for drug development

Schistosomiasis is a tropical disease caused by a flatworm trematode parasite that infects over 200 million people worldwide. Treatment and control of the disease rely on just one drug, praziquantel. The possibility of drug resistance coupled with praziquantel's variable efficacy encourages the identification of new drugs and drug targets. Disruption of neuromuscular homeostasis in parasitic worms is a validated strategy for drug development. In schistosomes, however, much remains to be understood about the organization of the nervous system, its component neurotransmitters and potential for drug discovery. Using synapsin as a neuronal marker, we map the central and peripheral nervous systems in the Schistosoma mansoni adult and schistosomulum (post-infective larva). We discover the widespread presence of octopamine (OA), a tyrosine-derived and invertebrate-specific neurotransmitter involved in neuromuscular coordination. OA labeling facilitated the discovery of two pairs of ganglia in the brain of the adult schistosome, rather than the one pair thus far reported for this and other trematodes. In quantitative phenotypic assays, OA and the structurally related tyrosine-derived phenolamine and catecholamine neurotransmitters differentially modulated schistosomulum motility and length. Similarly, from a screen of 28 drug agonists and antagonists of tyrosine-derivative signaling, certain drugs that act on OA and dopamine receptors induced robust and sometimes complex concentration-dependent effects on schistosome motility and length; in some cases, these effects occurred at concentrations achievable in vivo The present data advance our knowledge of the organization of the nervous system in this globally important pathogen and identify a number of drugs that interfere with tyrosine-derivative signaling, one or more of which might provide the basis for a new chemotherapeutic approach to treat schistosomiasis.This article has an associated First Person interview with the first author of the paper.

Allosteric binding site in a Cys-loop receptor ligand-binding domain unveiled in the crystal structure of ELIC in complex with chlorpromazine

Pentameric ligand-gated ion channels or Cys-loop receptors are responsible for fast inhibitory or excitatory synaptic transmission. The antipsychotic compound chlorpromazine is a widely used tool to probe the ion channel pore of the nicotinic acetylcholine receptor, which is a prototypical Cys-loop receptor. In this study, we determine the molecular determinants of chlorpromazine binding in the Erwinia ligand-gated ion channel (ELIC). We report the X-ray crystal structures of ELIC in complex with chlorpromazine or its brominated derivative bromopromazine. Unexpectedly, we do not find a chlorpromazine molecule in the channel pore of ELIC, but behind the β8-β9 loop in the extracellular ligand-binding domain. The β8-β9 loop is localized downstream from the neurotransmitter binding site and plays an important role in coupling of ligand binding to channel opening. In combination with electrophysiological recordings from ELIC cysteine mutants and a thiol-reactive derivative of chlorpromazine, we demonstrate that chlorpromazine binding at the β8-β9 loop is responsible for receptor inhibition. We further use molecular-dynamics simulations to support the X-ray data and mutagenesis experiments. Together, these data unveil an allosteric binding site in the extracellular ligand-binding domain of ELIC. Our results extend on previous observations and further substantiate our understanding of a multisite model for allosteric modulation of Cys-loop receptors.

Chlorpromazine confers neuroprotection against brain ischemia by activating BKCa channel

Chlorpromazine (CPZ) is a well-known antipsychotic drug, still widely being used to treat symptoms of schizophrenia, psychotic depression and organic psychoses. We have previously reported that CPZ activates the BKCa (KCa1.1) channel at whole cell level. In the present study, we demonstrated that CPZ increased the single channel open probability of the BKCa channels without changing its single channel amplitude. As BKCa channel is one of the molecular targets of brain ischemia, we explored a possible new use of this old drug on ischemic brain injury. In middle cerebral artery occlusion (MCAO) focal cerebral ischemia, a single intraperitoneal injection of CPZ at several dosages (5mg/kg, 10mg/kg and 20mg/kg) could exert a significant neuroprotective effect on the brain damage in a dose- and time-dependent manner. Furthermore, blockade of BKCa channels abolished the neuroprotective effect of CPZ on MCAO, suggesting that the effect of CPZ is mediated by activation of the BKCa channel. These results demonstrate that CPZ could reduce focal cerebral ischemic damage through activating BKCa channels and merits exploration as a potential therapeutic agent for treating ischemic stroke.

Lipid stress at play: mechanosensitivity of voltage-gated channels

Membrane stretch modulates the activity of voltage-gated channels (VGCs). These channels are nearly ubiquitous among eukaryotes and they are present, too, in prokaryotes, so the potential ramifications of VGC mechanosensitivity are diverse. In situ traumatic stretch can irreversibly alter VGC activity with lethal results but that is pathology. This chapter discusses the reversible responses of VGCs to stretch, with the general relation of stretch stimuli to other forms of lipid stress, and briefly, with some irreversible stretch effects (=stretch trauma). A working assumption throughout is that mechanosensitive (MS) VGC motions-that is, motions that respond reversibly to bilayer stretch-are susceptible to other forms of lipid stress, such as the stresses produced when amphiphilic molecules (anesthetics, lipids, alcohols, and lipophilic drugs) are inserted into the bilayer. Insofar as these molecules change the bilayer's lateral pressure profile, they can be termed bilayer mechanical reagents (BMRs). The chapter also discusses the MS VGC behavior against the backdrop of eukaryotic channels more widely accepted as "MS channels"--namely, the transient receptor potential (TRP)-based MS cation channels.

Chlorpromazine, clozapine and olanzapine inhibit anionic amino acid transport in cultured human fibroblasts

We report here that chlorpromazine, a first generation antipsychotic drug, inhibits anionic amino acid transport mediated by system X(-) (AG) (EAAT transporters) in cultured human fibroblasts. With 30 microM chlorpromazine, transport inhibition is detectable after 3 h of treatment, maximal after 48 h (>60%), and referable to a decrease in V(max). Chlorpromazine effect is not dependent upon changes of membrane potential and is selective for system X(-) (AG) since transport systems A and y(+) are not affected. Among antipsychotic drugs, the inhibitory effect of chlorpromazine is shared by two dibenzodiazepines, clozapine and olanzapine, while other compounds, such as risperidon, zuclopentixol, sertindol and haloperidol, are not effective. Transport inhibition by clozapine and olanzapine, but not by chlorpromazine, is reversible, suggesting that the mechanisms involved are distinct. These results indicate that a subset of antipsychotic drugs inhibits EAAT transporters in non-nervous tissues and prompt further investigation on possible alterations of glutamate transport in peripheral tissues of schizophrenic patients.