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

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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.


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KChIP2 knock down reduces myocyte contractility.(A) Representative tracing of the change in distance between two consecutive sarcomeres during contraction. Cells were paced at a 500 ms cycle length for Ad.GFP (n = 26) or Ad.KChIP KD (n = 28) treated myocytes. Tracings were normalized to control cells. Summary data for (B) fractional shortening, (C) contraction duration at 50% amplitude, and (D) the time to peak contraction. Data presented as mean ± SEM; *P < 0.05, **P < 0.01; two-tailed Student’s t-test.
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pone.0175221.g002: KChIP2 knock down reduces myocyte contractility.(A) Representative tracing of the change in distance between two consecutive sarcomeres during contraction. Cells were paced at a 500 ms cycle length for Ad.GFP (n = 26) or Ad.KChIP KD (n = 28) treated myocytes. Tracings were normalized to control cells. Summary data for (B) fractional shortening, (C) contraction duration at 50% amplitude, and (D) the time to peak contraction. Data presented as mean ± SEM; *P < 0.05, **P < 0.01; two-tailed Student’s t-test.

Mentions: Coinciding with the reduction in calcium release, myocyte contractility was also compromised. With KChIP2 loss we observed a decrease in fractional shortening from 5.47 ± 0.50 in control cells to 3.63 ± 0.44% in KChIP2 KD (Fig 2A and 2B). No changes were seen to the duration or the rate of contraction between treatment groups (Fig 2C and 2D). Yet, we clearly see that with KChIP2 loss, Ca2+ release and contraction are weakened. Notably, SR Ca2+ content was assessed by caffeine stimulation showing no change between treatment groups (Fig 3A and 3B), indicating the reduction in transient amplitude is not from a loss in SR Ca2+.


KChIP2 regulates the cardiac Ca 2+ transient and myocyte contractility by targeting ryanodine receptor activity
KChIP2 knock down reduces myocyte contractility.(A) Representative tracing of the change in distance between two consecutive sarcomeres during contraction. Cells were paced at a 500 ms cycle length for Ad.GFP (n = 26) or Ad.KChIP KD (n = 28) treated myocytes. Tracings were normalized to control cells. Summary data for (B) fractional shortening, (C) contraction duration at 50% amplitude, and (D) the time to peak contraction. 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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Show All Figures
getmorefigures.php?uid=PMC5383259&req=5

pone.0175221.g002: KChIP2 knock down reduces myocyte contractility.(A) Representative tracing of the change in distance between two consecutive sarcomeres during contraction. Cells were paced at a 500 ms cycle length for Ad.GFP (n = 26) or Ad.KChIP KD (n = 28) treated myocytes. Tracings were normalized to control cells. Summary data for (B) fractional shortening, (C) contraction duration at 50% amplitude, and (D) the time to peak contraction. Data presented as mean ± SEM; *P < 0.05, **P < 0.01; two-tailed Student’s t-test.
Mentions: Coinciding with the reduction in calcium release, myocyte contractility was also compromised. With KChIP2 loss we observed a decrease in fractional shortening from 5.47 ± 0.50 in control cells to 3.63 ± 0.44% in KChIP2 KD (Fig 2A and 2B). No changes were seen to the duration or the rate of contraction between treatment groups (Fig 2C and 2D). Yet, we clearly see that with KChIP2 loss, Ca2+ release and contraction are weakened. Notably, SR Ca2+ content was assessed by caffeine stimulation showing no change between treatment groups (Fig 3A and 3B), indicating the reduction in transient amplitude is not from a loss in SR Ca2+.

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