Arrhythmogenic Biophysical Phenotype for SCN5A Mutation S1787N Depends upon Splice Variant Background and Intracellular Acidosis

Abstract

Background SCN5A is a susceptibility gene for type 3 long QT syndrome, Brugada syndrome, and sudden infant death syndrome. I Na dysfunction from mutated SCN5A can depend upon the splice variant background in which it is expressed and also upon environmental factors such as acidosis. S1787N was reported previously as a LQT3-associated mutation and has also been observed in 1 of 295 healthy white controls. Here, we determined the in vitro biophysical phenotype of SCN5A-S1787N in an effort to further assess its possible pathogenicity.Methods and ResultsWe engineered S1787N in the two most common alternatively spliced SCN5A isoforms, the major isoform lacking a glutamine at position 1077 (Q1077del) and the minor isoform containing Q1077, and expressed these two engineered constructs in HEK293 cells for electrophysiological study. Macroscopic voltage-gated I Na was measured 24 hours after transfection with standard whole-cell patch clamp techniques. We applied intracellular solutions with pH7.4 or pH6.7. S1787N in the Q1077 background had WT-like I Na including peak I Na density, activation and inactivation parameters, and late I Na amplitude in both pH 7.4 and pH 6.7. However, with S1787N in the Q1077del background, the percentages of I Na late/peak were increased by 2.1 fold in pH 7.4 and by 2.9 fold in pH 6.7 when compared to WT.ConclusionThe LQT3-like biophysical phenotype for S1787N depends on both the SCN5A splice variant and on the intracellular pH. These findings provide further evidence that the splice variant and environmental factors affect the molecular phenotype of cardiac SCN5A-encoded sodium channel (Nav1.5), has implications for the clinical phenotype, and may provide insight into acidosis-induced arrhythmia mechanisms.

Channelopathy as a SUDEP Biomarker in Dravet Syndrome Patient-Derived Cardiac Myocytes

“…When compared with non-failing adult human heart, there were no differences in total SCN5A , SCN5A-6 , or SCN5A-6A expression ( Figure S3 B). We also investigated several common polymorphisms in SCN5A that are known to result in gain or loss of function, depending on the presence of other genetic mutations ( Ackerman et al., 2004 , Cheng et al., 2011 , Hu et al., 2015 , Kapplinger et al., 2015 , Makielski et al., 2003 , Shinlapawittayatorn et al., 2011 , Ye et al., 2003 ). We tested the four most likely polymorphisms S524Y, H558R, 1077del, or R1193Q.…”

Mexiletine rescues a mixed biophysical phenotype of the cardiac sodium channel arising from the SCN5A mutation, N406K, found in LQT3 patients

“…The dramatic increased late I Na found for SCN5A-N406K is typical of LQT3 [20]. The persistent Na current during action potential plateau is due to the failure of fast Na channel inactivation [8].…”

Mechanisms and models of cardiac sodium channel inactivation

“…109 Other groups have shown that certain long QT type 3 syndrome mutations are more sensitive to intracellular acidosis than others. 111 Another environmental factor modulating the Na C channel is body temperature. In healthy humans, without underlying mutations in Na v 1.5 or other conditions, temperature-dependent cardiac abnormalities may occur in extreme hyperthermia but seldom when they experience a mild fever.…”