RGD Reference Report - Molecular composition and heterogeneity of the LRRC8-containing swelling-activated osmolyte channels in primary rat astrocytes. - Rat Genome Database

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Molecular composition and heterogeneity of the LRRC8-containing swelling-activated osmolyte channels in primary rat astrocytes.

Authors: Schober, Alexandra L  Wilson, Corinne S  Mongin, Alexander A 
Citation: Schober AL, etal., J Physiol. 2017 Nov 15;595(22):6939-6951. doi: 10.1113/JP275053. Epub 2017 Sep 12.
RGD ID: 13673739
Pubmed: PMID:28833202   (View Abstract at PubMed)
PMCID: PMC5685816   (View Article at PubMed Central)
DOI: DOI:10.1113/JP275053   (Journal Full-text)


KEY POINTS: The volume-regulated anion channel (VRAC) is a swelling-activated chloride channel that is permeable to inorganic anions and a variety of small organic molecules. VRAC is formed via heteromerization of LRRC8 proteins, among which LRRC8A is essential, while LRRC8B/C/D/E serve as exchangeable complementary partners. We used an RNAi approach and radiotracer assays to explore which LRRC8 isoforms contribute to swelling-activated release of diverse organic osmolytes in rat astrocytes. Efflux of uncharged osmolytes (myo-inositol and taurine) was suppressed by deletion of LRRC8A or LRRC8D, but not by deletion of LRRC8C+LRRC8E. Conversely, release of charged osmolytes (d-aspartate) was strongly reduced by deletion of LRRC8A or LRRC8C+LRRC8E, but largely unaffected by downregulation of LRRC8D. Our findings point to the existence of multiple heteromeric VRACs in the same cell type: LRRC8A/D-containing heteromers appear to dominate release of uncharged osmolytes, while LRRC8A/C/E, with the additional contribution of LRRC8D, creates a conduit for movement of charged molecules.
ABSTRACT: The volume-regulated anion channel (VRAC) is the ubiquitously expressed vertebrate Cl- /anion channel that is composed of proteins belonging to the LRRC8 family and activated by cell swelling. In the brain, VRAC contributes to physiological and pathological release of a variety of small organic molecules, including the amino acid neurotransmitters glutamate, aspartate and taurine. In the present work, we explored the role of all five LRRC8 family members in the release of organic osmolytes from primary rat astrocytes. Expression of LRRC8 proteins was modified using an RNAi approach, and amino acid fluxes via VRAC were quantified by radiotracer assays in cells challenged with hypoosmotic medium (30% reduction in osmolarity). Consistent with our prior work, knockdown of LRRC8A potently and equally suppressed the release of radiolabelled d-[14 C]aspartate and [3 H]taurine. Among other LRRC8 subunits, downregulation of LRRC8D strongly inhibited release of the uncharged osmolytes [3 H]taurine and myo-[3 H]inositol, without major impact on the simultaneously measured efflux of the charged d-[14 C]aspartate. In contrast, the release of d-[14 C]aspartate was preferentially sensitive to deletion of LRRC8C+LRRC8E, but unaffected by downregulation of LRRC8D. Finally, siRNA knockdown of LRRC8C+LRRC8D strongly inhibited the release of all osmolytes. Overall, our findings suggest the existence of at least two distinct heteromeric VRACs in astroglial cells. The LRRC8A/D-containing permeability pathway appears to dominate the release of uncharged osmolytes, while an alternative channel (or channels) is composed of LRRC8A/C/D/E and responsible for the loss of charged molecules.



Gene Ontology Annotations    Click to see Annotation Detail View

Biological Process

  

Cellular Component

  
Object SymbolSpeciesTermQualifierEvidenceWithNotesSourceOriginal Reference(s)
Lrrc8cRatmonoatomic ion channel complex part_ofIMP PMID:28833202UniProt 
Lrrc8dRatmonoatomic ion channel complex part_ofIMP PMID:28833202UniProt 

Molecular Function

  
Object SymbolSpeciesTermQualifierEvidenceWithNotesSourceOriginal Reference(s)
Lrrc8aRatvolume-sensitive anion channel activity enablesIMP PMID:28833202UniProt 
Lrrc8cRatvolume-sensitive anion channel activity contributes_toIMP PMID:28833202UniProt 
Lrrc8dRatvolume-sensitive anion channel activity contributes_toIMP PMID:28833202UniProt 

Objects Annotated

Genes (Rattus norvegicus)
Lrrc8a  (leucine rich repeat containing 8 VRAC subunit A)
Lrrc8c  (leucine rich repeat containing 8 VRAC subunit C)
Lrrc8d  (leucine rich repeat containing 8 VRAC subunit D)


Additional Information