Identification and functional characterization of Kir2.6 mutations associated with non-familial hypokalemic periodic paralysis

Chih Jen Cheng, Shih Hua Lin, Yi Fen Lo, Sung Sen Yang, Yu Juei Hsu, Stephen C. Cannon, Chou Long Huang

Research output: Contribution to journalArticle

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Abstract

Hypokalemic periodic paralysis (hypoKPP) is characterized by episodic flaccid paralysis of muscle and acute hypokalemia during attacks. Familial forms of hypoKPP are predominantly caused by mutations of either voltage-gated Ca2 + or Na + channels. The pathogenic gene mutation in non-familial hypoKPP, consisting mainly of thyrotoxic periodic paralysis (TPP) and sporadic periodic paralysis (SPP), is largely unknown. Recently, mutations in KCNJ18, which encodes a skeletal muscle-specific inwardly rectifying K + channel Kir2.6, were reported in some TPP patients. Whether mutations of Kir2.6 occur in other patients with non-familial hypoKPP and how mutations of the channel predispose patients to paralysis are unknown. Here, we report one conserved heterozygous mutation in KCNJ18 in two TPP patients and two separate heterozygous mutations in two SPP patients. These mutations result in V168M, R43C, and A200P amino acid substitution of Kir2.6, respectively. Compared with the wild type channel, whole-cell currents of R43C and V168M mutants were reduced by ∼78 and 43%, respectively. No current was detected for the A200P mutant. Single channel conductance and open probability were reduced for R43C and V168M, respectively. Biotinylation assays showed reduced cell surface abundance for R43C and A200P. All three mutants exerted dominant negative inhibition on wild type Kir2.6 as well as wild type Kir2.1, another Kir channel expressed in the skeletal muscle. Thus, mutations of Kir2.6 are associated with SPP as well as TPP. We suggest that decreased outward K + current from hypofunction of Kir2.6 predisposes the sarcolemma to hypokalemia-induced paradoxical depolarization during attacks, which in turn leads to Na + channel inactivation and inexcitability of muscles.

Original languageEnglish (US)
Pages (from-to)27425-27435
Number of pages11
JournalJournal of Biological Chemistry
Volume286
Issue number31
DOIs
StatePublished - Aug 5 2011

Fingerprint

Hypokalemic Periodic Paralysis
Paralysis
Muscle
Mutation
Inwardly Rectifying Potassium Channel
Depolarization
Hypokalemia
Assays
Substitution reactions
Genes
Skeletal Muscle
Amino Acids
Biotinylation
Muscles
Sarcolemma
Electric potential
Amino Acid Substitution

ASJC Scopus subject areas

  • Biochemistry
  • Cell Biology
  • Molecular Biology

Cite this

Identification and functional characterization of Kir2.6 mutations associated with non-familial hypokalemic periodic paralysis. / Cheng, Chih Jen; Lin, Shih Hua; Lo, Yi Fen; Yang, Sung Sen; Hsu, Yu Juei; Cannon, Stephen C.; Huang, Chou Long.

In: Journal of Biological Chemistry, Vol. 286, No. 31, 05.08.2011, p. 27425-27435.

Research output: Contribution to journalArticle

Cheng, Chih Jen ; Lin, Shih Hua ; Lo, Yi Fen ; Yang, Sung Sen ; Hsu, Yu Juei ; Cannon, Stephen C. ; Huang, Chou Long. / Identification and functional characterization of Kir2.6 mutations associated with non-familial hypokalemic periodic paralysis. In: Journal of Biological Chemistry. 2011 ; Vol. 286, No. 31. pp. 27425-27435.
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abstract = "Hypokalemic periodic paralysis (hypoKPP) is characterized by episodic flaccid paralysis of muscle and acute hypokalemia during attacks. Familial forms of hypoKPP are predominantly caused by mutations of either voltage-gated Ca2 + or Na + channels. The pathogenic gene mutation in non-familial hypoKPP, consisting mainly of thyrotoxic periodic paralysis (TPP) and sporadic periodic paralysis (SPP), is largely unknown. Recently, mutations in KCNJ18, which encodes a skeletal muscle-specific inwardly rectifying K + channel Kir2.6, were reported in some TPP patients. Whether mutations of Kir2.6 occur in other patients with non-familial hypoKPP and how mutations of the channel predispose patients to paralysis are unknown. Here, we report one conserved heterozygous mutation in KCNJ18 in two TPP patients and two separate heterozygous mutations in two SPP patients. These mutations result in V168M, R43C, and A200P amino acid substitution of Kir2.6, respectively. Compared with the wild type channel, whole-cell currents of R43C and V168M mutants were reduced by ∼78 and 43{\%}, respectively. No current was detected for the A200P mutant. Single channel conductance and open probability were reduced for R43C and V168M, respectively. Biotinylation assays showed reduced cell surface abundance for R43C and A200P. All three mutants exerted dominant negative inhibition on wild type Kir2.6 as well as wild type Kir2.1, another Kir channel expressed in the skeletal muscle. Thus, mutations of Kir2.6 are associated with SPP as well as TPP. We suggest that decreased outward K + current from hypofunction of Kir2.6 predisposes the sarcolemma to hypokalemia-induced paradoxical depolarization during attacks, which in turn leads to Na + channel inactivation and inexcitability of muscles.",
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AU - Cheng, Chih Jen

AU - Lin, Shih Hua

AU - Lo, Yi Fen

AU - Yang, Sung Sen

AU - Hsu, Yu Juei

AU - Cannon, Stephen C.

AU - Huang, Chou Long

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