Figure 1.
Men are denoted by squares and women by circles. Solid symbols indicate mutation carriers, symbols with an “N” means wild type and “?” possible affected, crossed symbols denotes patients, who are already dead. A “-“ at the symbols indicates that no DNA is available, the propositus is marked with an arrow.
Figure 2.
Clinical and genetic characterization.
(A) Electropherogram of SCN5A mutation c.4477–4479delAAG and multiple sequence alignment of amino acids of human SCN5A protein regions bearing the identified in-frame deletion mutation of lysine (p.1492delK) with corresponding SCN5A amino acid sequences of different species. (B) Electrocardiogram of patient 10021_49 shows an atrioventricular block first-degree, an increased P-wave duration and an intraventricular conduction delay (P interval 145 ms, PQ interval 208 ms, QRS interval 146 ms). (C) Ajmaline challenge of patient 10021_149, overall 54 mg ajmaline (1mg/kg) was administered within 5 minutes. No Brugada type I ECG could be unmasked, but cardiac conduction delay aggravated.
Table 1.
Clinical and Genetic Characteristics of SCN5A 1493delK Carriers.
Table 2.
Electrocardiogram Parameters of Mutation or Obligate Mutation Carriers.
Figure 3.
1493delK mutant and wild-type (WT) human cardiac sodium channel current expressed in HEK293 cells.
(A) Whole-cell sodium current traces in response to increasing step depolarizations in WT (left) and 1493delK (right). (B) Voltage protocols for activation and steady-state inactivation. (C) Averaged sodium current– voltage relation for WT and 1493delK sodium channels. (D) Bar histogram showing averaged WT and 1493delK sodium peak currents at −20 mV. (E) Average voltage-dependence of activation and steady-state inactivation for wild-type (WT) and 1493delK sodium channels. For the activation curve, normalized peak conductance was plotted as a function of the membrane potential. For the inactivation curve, peak sodium currents were normalized to maximum values in each cell and plotted as a function of the voltage of the conditioning step.
Figure 4.
Inactivation kinetics of 1493delK mutant and wild-type (WT) human cardiac sodium channels.
(A) Time course of current decay. (A-i) Fast and slow time constants of current decay for WT and 1493delK sodium channels are plotted as a function of membrane potential. Asterisks indicate statistical significance (p<0.05). (A-ii) Ratio of the amplitudes of fast and slow inactivation time constants plotted as a function of voltage for WT and 1493delK sodium channels. (B) Time course of recovery from inactivation for WT and 1493delK sodium channels. Peak sodium currents elicited by P2 were normalized (P2/P1) and plotted as a function of the recovery interval. Inset: 2-pulse protocol. (C) Development of slow inactivation for WT and 1493delK sodium channels. Peak sodium currents elicited by P2 were normalized (P2/P1) and plotted as a function of the duration of the conditioning step (P1). Inset: 2-pulse protocol.
Table 3.
Electrophysiological characteristics of WT and 1493delK mutant sodium channels in HEK293 cells.
Figure 5.
Sodium channel membrane expression in wild-type and mutant 1493delK SCN5A-transfected HEK293 cells.
Confocal immunofluorescence of the a-subunit of cardiac sodium channel (NaV1.5) and the endoplasmic reticulum transmembrane protein calnexin in HEK293 expressing WT (left) and mutant 1493delK (right) sodium channels. Top and middle panels show staining with anti-NaV1.5 (green) and anti-calnexin (red) respectively. Bottom panels show overlay of red and green channels of double staining with anti-NaV1.5 (green) and anti-calnexin (red) antibodies. Membrane labeling for NaV1.5 is observed as a clearly distinguishable green rim surrounding the intracellularly located calnexin (red) in WT SCN5A transfected HEK293 cells, whereas mutant 1493delK SCN5A transfected HEK293 cells do not show clear cell-surface labeling, but mostly cytoplasmic NaV1.5 staining. Scale bars indicate 25 µm.
Figure 6.
Topological model of the cardiac sodium channel (NaV1.5).
Location of the mutations in the linker region between domains DIII and DIV that is responsible for the inactivation of the channel.