Hypertension resistance polymorphisms in ROMK (Kir1.1) alter channel function by different mechanisms

Liang Fang, Dimin Li, Paul A. Welling

Research output: Contribution to journalArticle

Abstract

The renal outer medullary K+ (ROMK) channel plays a critical role in renal sodium handling. Recent genome sequencing efforts in the Framingham Heart Study offspring cohort (Ji W, Foo JN, O'Roak BJ, Zhao H, Larson MG, Simon DB, Newton-Cheh C, State MW, Levy D, and Lifton RP. Nat Genet 40: 592-599, 2008) recently revealed an association between suspected loss-of-function polymorphisms in the ROMK channel and resistance to hypertension, suggesting that ROMK activity may also be a determinant of blood pressure control in the general population. Here we examine whether these sequence variants do, in fact, alter ROMK channel function and explore the mechanisms. As assessed by two-microelectrode voltage clamp in Xenopus oocytes, 3/5 of the variants (R193P, H251Y, and T313FS) displayed an almost complete attenuation of whole cell ROMK channel activity. Surface antibody binding measurements of external epitope-tagged channels and analysis of glycosylation-state maturation revealed that these variants prevent channel expression at the plasmalemma, likely as a consequence of retention in the endoplasmic reticulum. The other variants (P166S, R169H) had no obvious effects on the basal channel activity or surface expression but, instead, conferred a gain in regulated-inhibitory gating. As assessed in giant excised patch-clamp studies, apparent phosphotidylinositol 4,5-bisphosphate (PIP2) binding affinity of the variants was reduced, causing channels to be more susceptible to inhibition upon PIP2 depletion. Unlike the protein product of the major ROMK allele, these two variants are sensitive to the inhibitory affects of a G protein-coupled receptor, which stimulates PIP 2 hydrolysis. In summary, we have found that hypertension resistance sequence variants inhibit ROMK channel function by different mechanisms, providing new insights into the role of the channel in the maintenance of blood pressure.

Original languageEnglish (US)
Pages (from-to)F1359-F1364
JournalAmerican Journal of Physiology - Renal Physiology
Volume299
Issue number6
DOIs
StatePublished - Dec 1 2010
Externally publishedYes

Fingerprint

Hypertension
Kidney
Blood Pressure
Viverridae
Renal Hypertension
Microelectrodes
G-Protein-Coupled Receptors
Xenopus
Glycosylation
Endoplasmic Reticulum
Oocytes
Epitopes
Hydrolysis
Cohort Studies
Sodium
Alleles
Maintenance
Genome
Antibodies
Population

Keywords

  • Bartter
  • Blood pressure
  • Inward rectified potassium channel 1.1
  • Inward rectifier
  • Misfolded protein
  • Phosphotidylinositol 4,5-bisphosphate
  • Potassium channel

ASJC Scopus subject areas

  • Physiology
  • Urology

Cite this

Hypertension resistance polymorphisms in ROMK (Kir1.1) alter channel function by different mechanisms. / Fang, Liang; Li, Dimin; Welling, Paul A.

In: American Journal of Physiology - Renal Physiology, Vol. 299, No. 6, 01.12.2010, p. F1359-F1364.

Research output: Contribution to journalArticle

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abstract = "The renal outer medullary K+ (ROMK) channel plays a critical role in renal sodium handling. Recent genome sequencing efforts in the Framingham Heart Study offspring cohort (Ji W, Foo JN, O'Roak BJ, Zhao H, Larson MG, Simon DB, Newton-Cheh C, State MW, Levy D, and Lifton RP. Nat Genet 40: 592-599, 2008) recently revealed an association between suspected loss-of-function polymorphisms in the ROMK channel and resistance to hypertension, suggesting that ROMK activity may also be a determinant of blood pressure control in the general population. Here we examine whether these sequence variants do, in fact, alter ROMK channel function and explore the mechanisms. As assessed by two-microelectrode voltage clamp in Xenopus oocytes, 3/5 of the variants (R193P, H251Y, and T313FS) displayed an almost complete attenuation of whole cell ROMK channel activity. Surface antibody binding measurements of external epitope-tagged channels and analysis of glycosylation-state maturation revealed that these variants prevent channel expression at the plasmalemma, likely as a consequence of retention in the endoplasmic reticulum. The other variants (P166S, R169H) had no obvious effects on the basal channel activity or surface expression but, instead, conferred a gain in regulated-inhibitory gating. As assessed in giant excised patch-clamp studies, apparent phosphotidylinositol 4,5-bisphosphate (PIP2) binding affinity of the variants was reduced, causing channels to be more susceptible to inhibition upon PIP2 depletion. Unlike the protein product of the major ROMK allele, these two variants are sensitive to the inhibitory affects of a G protein-coupled receptor, which stimulates PIP 2 hydrolysis. In summary, we have found that hypertension resistance sequence variants inhibit ROMK channel function by different mechanisms, providing new insights into the role of the channel in the maintenance of blood pressure.",
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