title: Calcium-sensing receptor decreases cell surface expression of the inwardly rectifying K+ channel Kir4.1.
abstract: The Ca(2+)-sensing receptor (CaR) regulates salt and water transport in the kidney as demonstrated by the association of gain of function CaR mutations with a Bartter syndrome-like, salt-wasting phenotype, but the precise mechanism for this effect is not fully established. We found previously that the CaR interacts with and inactivates an inwardly rectifying K(+) channel, Kir4.1, which is expressed in the distal nephron that contributes to the basolateral K(+) conductance, and in which loss of function mutations are associated with a complex phenotype that includes renal salt wasting. We now find that CaR inactivates Kir4.1 by reducing its cell surface expression. Mutant CaRs reduced Kir4.1 cell surface expression and current density in HEK-293 cells in proportion to their signaling activity. Mutant, activated Gα(q) reduced cell surface expression and current density of Kir4.1, and these effects were blocked by RGS4, a protein that blocks signaling via Gα(i) and Gα(q). Other α subunits had insignificant effects. Knockdown of caveolin-1 blocked the effect of Gα(q) on Kir4.1, whereas knockdown of the clathrin heavy chain had no effect. CaR had no comparable effect on the renal outer medullary K(+) channel, an apical membrane distal nephron K(+) channel that is internalized by clathrin-coated vesicles. Co-immunoprecipitation studies showed that the CaR and Kir4.1 physically associate with caveolin-1 in HEK cells and in kidney extracts. Thus, the CaR decreases cell surface expression of Kir4.1 channels via a mechanism that involves Gα(q) and caveolin. These results provide a novel molecular basis for the inhibition of renal NaCl transport by the CaR.
authors.affiliation: Department of Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
authors.forename: Seung-Kuy
authors.initials: SK
authors.lastname: Cha
authors.forename: Chunfa
authors.initials: C
authors.lastname: Huang
authors.forename: Yaxian
authors.initials: Y
authors.lastname: Ding
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Qi
authors.forename: Chou-Long
authors.initials: CL
authors.lastname: Huang
authors.forename: R Tyler
authors.initials: RT
authors.lastname: Miller
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000235:genetics; D051242:Caveolin 1 / Q000235:genetics / Q000378:metabolism; D033922:Clathrin Heavy Chains / Q000235:genetics / Q000378:metabolism; D022163:Clathrin-Coated Vesicles / Q000235:genetics / Q000378:metabolism; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D006801:Humans; D009399:Nephrons / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying / Q000096:biosynthesis* / Q000235:genetics; D051381:Rats; D044169:Receptors, Calcium-Sensing / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D012965:Sodium Chloride / Q000378:metabolism*; D014883:Water-Electrolyte Imbalance / Q000235:genetics / Q000378:metabolism; D000098854:Kcnj10 Channel
chemical_list: C495540:CAV1 protein, human; C495537:Cav1 protein, rat; D051242:Caveolin 1; D000098854:Kcnj10 Channel; D024661:Potassium Channels, Inwardly Rectifying; D044169:Receptors, Calcium-Sensing; D033922:Clathrin Heavy Chains; D012965:Sodium Chloride; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D011188:Potassium