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Interaction of the Ca²⁺-sensing receptor with the inwardly rectifying potassium channels Kir4.1 and Kir4.2 results in inhibition of channel function

¹Department of Medicine and ²Department of Physiology and Biophysics, Case Western Reserve University, ³Louis Stokes Veterans Affairs Medical Center, and ⁴Rammelkamp Center for Research and Education, MetroHealth System Campus, Cleveland, Ohio; ⁵GI Diseases Research Unit, Hotel Dieu Hospital and Queen's University, Kingston, Ontario, Canada; ⁶The Water and Salt Research Center, University of Aarhus, Aarhus, Denmark; and ⁷Department of Pharmacology II, Osaka University, Osaka, Japan

Submitted 15 July 2006 ; accepted in final form 8 November 2006

The Ca²⁺-sensing receptor (CaR), a G protein-coupled receptor, is expressed in many epithelial tissues including the parathyroid glands, kidney, and GI tract. Although its role in regulating PTH levels and Ca²⁺ metabolism are best characterized, it may also regulate salt and water transport in the kidney as demonstrated by recent reports showing association of potent gain-of-function mutations in the CaR with a Bartter-like, salt-wasting phenotype. To determine whether this receptor interacts with novel proteins that control ion transport, we screened a human adult kidney cDNA library with the COOH-terminal 219 amino acid cytoplasmic tail of the CaR as bait using the yeast two-hybrid system. We identified two independent clones coding for 125 aa from the COOH terminus of the inwardly rectifying K⁺ channel, Kir4.2. The CaR and Kir4.2 as well as Kir4.1 (another member of Kir4 subfamily) were reciprocally coimmunoprecipitated from HEK-293 cells in which they were expressed, but the receptor did not coimmunoprecipitate with Kir5.1 or Kir1.1. Both Kir4.1 and Kir4.2 were immunoprecipitated from rat kidney extracts with the CaR. In Xenopus laevis oocytes, expression of the CaR with either Kir4.1 or Kir4.2 channels resulted in inactivation of whole cell current as measured by two-electrode voltage clamp, but the nonfunctional CaR mutant CaR^R796W, and that does not coimmunoprecipitate with the channels, had no effect. Kir4.1 and the CaR were colocalized in the basolateral membrane of the distal nephron. The CaR interacts directly with Kir4.1 and Kir4.2 and can decrease their currents, which in turn could reduce recycling of K⁺ for the basolateral Na⁺-K⁺-ATPase and thereby contribute to inhibition of Na⁺ reabsorption.

inwardly rectifying K⁺ channel; HEK 293 cells; yeast two hybrid

This article has been cited by other articles:

				A. Sindic, C. Huang, A.-P. Chen, Y. Ding, W. A. Miller-Little, D. Che, M. F. Romero, and R. T. Miller MUPP1 complexes renal K+ channels to alter cell surface expression and whole cell currents Am J Physiol Renal Physiol, July 1, 2009; 297(1): F36 - F45. [Abstract] [Full Text] [PDF]