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KChIP2 regulates the cardiac Ca 2+ transient and myocyte contractility by targeting ryanodine receptor activity

View Article: PubMed Central - PubMed

ABSTRACT

Pathologic electrical remodeling and attenuated cardiac contractility are featured characteristics of heart failure. Coinciding with these remodeling events is a loss of the K+ channel interacting protein, KChIP2. While, KChIP2 enhances the expression and stability of the Kv4 family of potassium channels, leading to a more pronounced transient outward K+ current, Ito,f, the guinea pig myocardium is unique in that Kv4 expression is absent, while KChIP2 expression is preserved, suggesting alternative consequences to KChIP2 loss. Therefore, KChIP2 was acutely silenced in isolated guinea pig myocytes, which led to significant reductions in the Ca2+ transient amplitude and prolongation of the transient duration. This change was reinforced by a decline in sarcomeric shortening. Notably, these results were unexpected when considering previous observations showing enhanced ICa,L and prolonged action potential duration following KChIP2 loss, suggesting a disruption of fundamental Ca2+ handling proteins. Evaluation of SERCA2a, phospholamban, RyR, and sodium calcium exchanger identified no change in protein expression. However, assessment of Ca2+ spark activity showed reduced spark frequency and prolonged Ca2+ decay following KChIP2 loss, suggesting an altered state of RyR activity. These changes were associated with a delocalization of the ryanodine receptor activator, presenilin, away from sarcomeric banding to more diffuse distribution, suggesting that RyR open probability are a target of KChIP2 loss mediated by a dissociation of presenilin. Typically, prolonged action potential duration and enhanced Ca2+ entry would augment cardiac contractility, but here we see KChIP2 fundamentally disrupts Ca2+ release events and compromises myocyte contraction. This novel role targeting presenilin localization and RyR activity reveals a significance for KChIP2 loss that reflects adverse remodeling observed in cardiac disease settings.

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KChIP2 knock down reduces Ca2+ transient amplitude.(A) Representative Ca2+ transient recordings taken from isolated adult guinea pig myocytes loaded with Indo-1 and paced at a 500 ms cycle length. Recordings were taken following 24 hrs treatment with an adenovirus encoding GFP (control, n = 17) or an mRNA antisense sequence for KChIP2 (Ad.KChIP2 KD, n = 17). Summary data for the (B) Ca2+ transient amplitude, (C) Ca2+ transient duration at 50% peak amplitude, and (D) the transient time-to-peak. Data presented as mean ± SEM; *P < 0.05, **P < 0.01; two-tailed Student’s t-test.
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pone.0175221.g001: KChIP2 knock down reduces Ca2+ transient amplitude.(A) Representative Ca2+ transient recordings taken from isolated adult guinea pig myocytes loaded with Indo-1 and paced at a 500 ms cycle length. Recordings were taken following 24 hrs treatment with an adenovirus encoding GFP (control, n = 17) or an mRNA antisense sequence for KChIP2 (Ad.KChIP2 KD, n = 17). Summary data for the (B) Ca2+ transient amplitude, (C) Ca2+ transient duration at 50% peak amplitude, and (D) the transient time-to-peak. Data presented as mean ± SEM; *P < 0.05, **P < 0.01; two-tailed Student’s t-test.

Mentions: We isolated adult guinea pig ventricular myocytes, which were subsequently treated with a control virus encoding GFP (control) or an antisense sequence for KChIP2 (KChIP2 KD) to acutely suppress expression as previously confirmed [8]. Following 24 hrs incubation, we evaluated the cells for changes to Ca2+ transients and contractility. In myocytes treated with KChIP2 KD we observed a significant reduction in Ca2+ transient amplitude by 18.8% (Ca2+ transient amplitude: control 1.11 ± 0.06 vs KChIP2 KD 0.90 ± 0.07 AU) (Fig 1A and 1B) at 0.5 Hz field stimulation. This change was accompanied by a significant prolongation of the Ca2+ transient duration (Fig 1C) but no change in the time-to-peak (Fig 1D). Remarkably, this reduction in Ca2+ transient amplitude and preservation of SR Ca2+ content occurred despite the presence of an increase in ICa,L [8], suggesting a potential impact of KChIP2 on calcium induced calcium release (CICR).


KChIP2 regulates the cardiac Ca 2+ transient and myocyte contractility by targeting ryanodine receptor activity
KChIP2 knock down reduces Ca2+ transient amplitude.(A) Representative Ca2+ transient recordings taken from isolated adult guinea pig myocytes loaded with Indo-1 and paced at a 500 ms cycle length. Recordings were taken following 24 hrs treatment with an adenovirus encoding GFP (control, n = 17) or an mRNA antisense sequence for KChIP2 (Ad.KChIP2 KD, n = 17). Summary data for the (B) Ca2+ transient amplitude, (C) Ca2+ transient duration at 50% peak amplitude, and (D) the transient time-to-peak. Data presented as mean ± SEM; *P < 0.05, **P < 0.01; two-tailed Student’s t-test.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5383259&req=5

pone.0175221.g001: KChIP2 knock down reduces Ca2+ transient amplitude.(A) Representative Ca2+ transient recordings taken from isolated adult guinea pig myocytes loaded with Indo-1 and paced at a 500 ms cycle length. Recordings were taken following 24 hrs treatment with an adenovirus encoding GFP (control, n = 17) or an mRNA antisense sequence for KChIP2 (Ad.KChIP2 KD, n = 17). Summary data for the (B) Ca2+ transient amplitude, (C) Ca2+ transient duration at 50% peak amplitude, and (D) the transient time-to-peak. Data presented as mean ± SEM; *P < 0.05, **P < 0.01; two-tailed Student’s t-test.
Mentions: We isolated adult guinea pig ventricular myocytes, which were subsequently treated with a control virus encoding GFP (control) or an antisense sequence for KChIP2 (KChIP2 KD) to acutely suppress expression as previously confirmed [8]. Following 24 hrs incubation, we evaluated the cells for changes to Ca2+ transients and contractility. In myocytes treated with KChIP2 KD we observed a significant reduction in Ca2+ transient amplitude by 18.8% (Ca2+ transient amplitude: control 1.11 ± 0.06 vs KChIP2 KD 0.90 ± 0.07 AU) (Fig 1A and 1B) at 0.5 Hz field stimulation. This change was accompanied by a significant prolongation of the Ca2+ transient duration (Fig 1C) but no change in the time-to-peak (Fig 1D). Remarkably, this reduction in Ca2+ transient amplitude and preservation of SR Ca2+ content occurred despite the presence of an increase in ICa,L [8], suggesting a potential impact of KChIP2 on calcium induced calcium release (CICR).

View Article: PubMed Central - PubMed

ABSTRACT

Pathologic electrical remodeling and attenuated cardiac contractility are featured characteristics of heart failure. Coinciding with these remodeling events is a loss of the K+ channel interacting protein, KChIP2. While, KChIP2 enhances the expression and stability of the Kv4 family of potassium channels, leading to a more pronounced transient outward K+ current, Ito,f, the guinea pig myocardium is unique in that Kv4 expression is absent, while KChIP2 expression is preserved, suggesting alternative consequences to KChIP2 loss. Therefore, KChIP2 was acutely silenced in isolated guinea pig myocytes, which led to significant reductions in the Ca2+ transient amplitude and prolongation of the transient duration. This change was reinforced by a decline in sarcomeric shortening. Notably, these results were unexpected when considering previous observations showing enhanced ICa,L and prolonged action potential duration following KChIP2 loss, suggesting a disruption of fundamental Ca2+ handling proteins. Evaluation of SERCA2a, phospholamban, RyR, and sodium calcium exchanger identified no change in protein expression. However, assessment of Ca2+ spark activity showed reduced spark frequency and prolonged Ca2+ decay following KChIP2 loss, suggesting an altered state of RyR activity. These changes were associated with a delocalization of the ryanodine receptor activator, presenilin, away from sarcomeric banding to more diffuse distribution, suggesting that RyR open probability are a target of KChIP2 loss mediated by a dissociation of presenilin. Typically, prolonged action potential duration and enhanced Ca2+ entry would augment cardiac contractility, but here we see KChIP2 fundamentally disrupts Ca2+ release events and compromises myocyte contraction. This novel role targeting presenilin localization and RyR activity reveals a significance for KChIP2 loss that reflects adverse remodeling observed in cardiac disease settings.

No MeSH data available.


Related in: MedlinePlus