Limits...
α1-Syntrophin Variant Identified in Drug-Induced Long QT Syndrome Increases Late Sodium Current.

Choi JI, Wang C, Thomas MJ, Pitt GS - PLoS ONE (2016)

Bottom Line: Few variants in the cardiac NaV1.5 Na+ channel complex have been associated with diLQTS.We tested whether a novel SNTA1 (α1-syntrophin) variant (p.E409Q) found in a patient with diLQTS increases late sodium current (INa-L), thereby providing a disease mechanism.In cardiomyocytes, INa-L was significantly increased by E409Q, but not by A390V compared to WT (0.49 ± 0.14 in WT vs.0.94 ± 0.23 in A390V, p = 0.099; vs. 1.12 ± 0.24 in E409Q, p = 0.019).

View Article: PubMed Central - PubMed

Affiliation: Division of Cardiology, Department of Medicine, Duke University School of Medicine; and Ion Channel Research Unit, Duke University Medical Center, Durham, NC, United States of America.

ABSTRACT
Drug-induced long-QT syndrome (diLQTS) is often due to drug block of IKr, especially in genetically susceptible patients with subclinical mutations in the IKr-encoding KCHN2. Few variants in the cardiac NaV1.5 Na+ channel complex have been associated with diLQTS. We tested whether a novel SNTA1 (α1-syntrophin) variant (p.E409Q) found in a patient with diLQTS increases late sodium current (INa-L), thereby providing a disease mechanism. Electrophysiological studies were performed in HEK293T cells co-expressing human NaV1.5/nNOS/PMCA4b with either wild type (WT) or SNTA1 variants (A390V-previously reported in congenital LQTS; and E409Q); and in adult rat ventricular cardiomyocytes infected with SNTA1 expressing adenoviruses (WT or one of the two SNTA1 variants). In HEK293T cells and in cardiomyocytes, there was no significant difference in the peak INa densities among the SNTA1 WT and variants. However, both variants increased INa-L (% of peak current) in HEK293T cells (0.58 ± 0.10 in WT vs. 0.90 ± 0.11 in A390V, p = 0.048; vs. 0.88 ± 0.07 in E409Q, p = 0.023). In cardiomyocytes, INa-L was significantly increased by E409Q, but not by A390V compared to WT (0.49 ± 0.14 in WT vs.0.94 ± 0.23 in A390V, p = 0.099; vs. 1.12 ± 0.24 in E409Q, p = 0.019). We demonstrated that a novel SNTA1 variant is likely causative for diLQTS by augmenting INa-L. These data suggest that variants within the NaV1.5-interacting α1-syntrophin are a potential mechanism for diLQTS, thereby expanding the concept that variants within congenital LQTS loci can cause diLQTS.

Show MeSH

Related in: MedlinePlus

Electrophysiological data of NaV1.5 in HEK293T cells coexpressing PMCA4b, nNOS, and either WT or SNTA1 mutants.(A) Representative traces of inward Na+ current for the 3 groups tested. (B) I-V curve. (C) Activation (G/Gmax). (D) Inactivation (I/Imax). (E) Recovery (P2/P1).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4814026&req=5

pone.0152355.g002: Electrophysiological data of NaV1.5 in HEK293T cells coexpressing PMCA4b, nNOS, and either WT or SNTA1 mutants.(A) Representative traces of inward Na+ current for the 3 groups tested. (B) I-V curve. (C) Activation (G/Gmax). (D) Inactivation (I/Imax). (E) Recovery (P2/P1).

Mentions: We recorded voltage-gated Na+ currents in HEK293T cells, in which we transiently co-expressed components of the Na+ channel macromolecular complex necessary for regulation by SNTA1. Specifically, we expressed human NaV1.5 (with a C373Y mutation rendering the channel sensitive to TTX), nNOS, and PMCA4b with WT SNTA1 or either of the two SNTA1 mutants. Previous studies have shown that the TTX-sensitive mutation does not affect any permeation properties.[30] Table 1 shows the summary data for the 3 groups. Representative traces of whole-cell currents (Fig 2A) and I-V curves (Fig 2B) show that neither mutant affected peak INa current density nor the kinetics of activation compared to WT-SNTA1 (Fig 2C). The k of inactivation was significantly reduced only in E409Q-SNTA1 (p<0.001). There was no significant difference in rate of fast recovery from inactivation using a two-pulse protocol among WT and the mutants, but the rate of slow recovery was significantly prolonged in A390V-SNTA1 compared to WT-SNTA1 (p = 0.035) (Fig 2D). Focusing only on the mutants, there was no significant difference in all parameters of activation, inactivation and recovery (Table 1).


α1-Syntrophin Variant Identified in Drug-Induced Long QT Syndrome Increases Late Sodium Current.

Choi JI, Wang C, Thomas MJ, Pitt GS - PLoS ONE (2016)

Electrophysiological data of NaV1.5 in HEK293T cells coexpressing PMCA4b, nNOS, and either WT or SNTA1 mutants.(A) Representative traces of inward Na+ current for the 3 groups tested. (B) I-V curve. (C) Activation (G/Gmax). (D) Inactivation (I/Imax). (E) Recovery (P2/P1).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4814026&req=5

pone.0152355.g002: Electrophysiological data of NaV1.5 in HEK293T cells coexpressing PMCA4b, nNOS, and either WT or SNTA1 mutants.(A) Representative traces of inward Na+ current for the 3 groups tested. (B) I-V curve. (C) Activation (G/Gmax). (D) Inactivation (I/Imax). (E) Recovery (P2/P1).
Mentions: We recorded voltage-gated Na+ currents in HEK293T cells, in which we transiently co-expressed components of the Na+ channel macromolecular complex necessary for regulation by SNTA1. Specifically, we expressed human NaV1.5 (with a C373Y mutation rendering the channel sensitive to TTX), nNOS, and PMCA4b with WT SNTA1 or either of the two SNTA1 mutants. Previous studies have shown that the TTX-sensitive mutation does not affect any permeation properties.[30] Table 1 shows the summary data for the 3 groups. Representative traces of whole-cell currents (Fig 2A) and I-V curves (Fig 2B) show that neither mutant affected peak INa current density nor the kinetics of activation compared to WT-SNTA1 (Fig 2C). The k of inactivation was significantly reduced only in E409Q-SNTA1 (p<0.001). There was no significant difference in rate of fast recovery from inactivation using a two-pulse protocol among WT and the mutants, but the rate of slow recovery was significantly prolonged in A390V-SNTA1 compared to WT-SNTA1 (p = 0.035) (Fig 2D). Focusing only on the mutants, there was no significant difference in all parameters of activation, inactivation and recovery (Table 1).

Bottom Line: Few variants in the cardiac NaV1.5 Na+ channel complex have been associated with diLQTS.We tested whether a novel SNTA1 (α1-syntrophin) variant (p.E409Q) found in a patient with diLQTS increases late sodium current (INa-L), thereby providing a disease mechanism.In cardiomyocytes, INa-L was significantly increased by E409Q, but not by A390V compared to WT (0.49 ± 0.14 in WT vs.0.94 ± 0.23 in A390V, p = 0.099; vs. 1.12 ± 0.24 in E409Q, p = 0.019).

View Article: PubMed Central - PubMed

Affiliation: Division of Cardiology, Department of Medicine, Duke University School of Medicine; and Ion Channel Research Unit, Duke University Medical Center, Durham, NC, United States of America.

ABSTRACT
Drug-induced long-QT syndrome (diLQTS) is often due to drug block of IKr, especially in genetically susceptible patients with subclinical mutations in the IKr-encoding KCHN2. Few variants in the cardiac NaV1.5 Na+ channel complex have been associated with diLQTS. We tested whether a novel SNTA1 (α1-syntrophin) variant (p.E409Q) found in a patient with diLQTS increases late sodium current (INa-L), thereby providing a disease mechanism. Electrophysiological studies were performed in HEK293T cells co-expressing human NaV1.5/nNOS/PMCA4b with either wild type (WT) or SNTA1 variants (A390V-previously reported in congenital LQTS; and E409Q); and in adult rat ventricular cardiomyocytes infected with SNTA1 expressing adenoviruses (WT or one of the two SNTA1 variants). In HEK293T cells and in cardiomyocytes, there was no significant difference in the peak INa densities among the SNTA1 WT and variants. However, both variants increased INa-L (% of peak current) in HEK293T cells (0.58 ± 0.10 in WT vs. 0.90 ± 0.11 in A390V, p = 0.048; vs. 0.88 ± 0.07 in E409Q, p = 0.023). In cardiomyocytes, INa-L was significantly increased by E409Q, but not by A390V compared to WT (0.49 ± 0.14 in WT vs.0.94 ± 0.23 in A390V, p = 0.099; vs. 1.12 ± 0.24 in E409Q, p = 0.019). We demonstrated that a novel SNTA1 variant is likely causative for diLQTS by augmenting INa-L. These data suggest that variants within the NaV1.5-interacting α1-syntrophin are a potential mechanism for diLQTS, thereby expanding the concept that variants within congenital LQTS loci can cause diLQTS.

Show MeSH
Related in: MedlinePlus