Differential Modulation of IK and ICa,L Channels in High-Fat Diet-Induced Obese Guinea Pig Atria

Figure 1. Electrophysiological properties of IK, IKur, IK1, and ICa,L currents in HFD atrial myocytes. (A) Representative IK traces from right atrial myocytes isolated from LFD-fed guinea pigs. (B) Exemplar IK currents measured in HFD atrial myocytes. (C) Population I-V curves for peak IK currents measured in LFD (●, n = 10) or HFD (○, n = 9) atrial myocytes. Exemplar currents and I-V relationships for indicated IKur (D–F), IK1 (G–I), and ICa,L (J–L), same format as (A–C). Data points are means ± S.E.M, n = 5–20. *p < 0.05. Data were generated from three different guinea pig cardiomyocyte preparations.

Figure 2. Electrical properties of guinea pig atrial myocytes and ex vivo hearts. (A) Examples of AP waveforms measured in right atrial myocytes isolated from LFD- (A) or HFD-fed (B) guinea pigs, or exposed to exogenous PA (1 mM, ≥1 h, C). HFD and PA pre-treated myocytes had a shortened action potential in line with the previous finding (Aromolaran et al., 2016). (D) Typical spontaneous beats with early delayed afterdepolarizations (EAD)-like activity measured in right atrial myocytes from HFD-fed guinea pigs. (E) Exemplar delayed repolarization with irregular and spontaneous beats in atrial myocytes pretreated with PA. Compared to control myocytes isolated from LFD-fed guinea pigs (F, white column), untreated (G, gold column) or pre-treated with OA (G, light gray column), the incidence of spontaneous beats is significantly greater in HFD (F, black column) and PA-treated myocytes (G, dark gray column). (H) Induction of arrhythmogenesis in right atria of isolated Langendorff perfused hearts from LFD- (left panel) and HFD-fed (right panel) guinea pigs. With rapid right atrial pacing (burst, rectangular pulses 10 ms, 1 V in amplitude with pulse-pulse duration ranging between 20 and 250 ms).…

Figure 3. Effects of burst pacing on membrane currents in cardiomyocytes isolated from the atria of LFD and HFD guinea pigs. (A) Selected IK tracings of myocytes from LFD atria after burst pacing. (B) IK currents measured in HFD-fed guinea pigs after burst pacing. (C) Pooled I-V plots for IK density in LFD (■, n = 10) and HFD (, n = 5) myocytes. Data for IK measured without atria pacing is reproduced for LFD (red trace) and HFD (cyan trace) from Figure 1C. (D–L) Exemplar currents and I-V curves for IKur, IK1, and ICa,L, same format as (A–C). IKur density is reduced (F) after pacing while IK1 density is increased (I). Each data point represents mean ± S.E.M, n = 5–20. *p < 0.05. Data were generated from six different guinea pig cardiomyocyte preparations.

Figure 4. Biophysical properties of IK in atrial myocytes isolated from LFD- and HFD-fed (with and without burst pacing) guinea pigs. (A) Normalized activation curves for IK in LFD (●, n = 10), HFD (○, n = 9), and HFD with pacing (■, n = 5). (B) Relationship between time course (τrise time) of activation and voltage. (C) Plot of the IK tail current deactivation (τdeactivation) relative to voltage. Gating properties of IK are altered with HFD alone or in combination with pacing. *p < 0.05 relative to LFD control myocytes. Unpaired Student’s t-test followed by one-way ANOVA.

Figure 5. Optical detection of surface hERG subunits with quantum dot in HEK293 cells. (A) Schematic of BBS- and YFP-tagged hERG 1a, CFP-tagged hERG 1b and YFP-tagged hERG 1a lacking the BBS tag. (B) Confocal images of non-permeabilized HEK293 cells expressing BBS-hERG 1a-YFP or hERG 1a-YFP alone and in combination with hERG 1b-CFP, and exposed to QD655 to selectively label surface channels. Panels show hERG channels for YFP (total expression, left panel), CFP (middle panel), and QD655 (surface channels, right panel). Scale bars represent 20 μm. (C) Normalized mean QD655 signals from YFP-positive cells expressing BBS-hERG 1a-YFP alone (white column), BBS-hERG 1a-YFP/hERG 1b-CFP (black column), and hERG 1a-YFP/hERG 1b-CFP (gray column) represent relative surface density. hERG 1a-YFP/hERG 1b-CFP serves as negative control and shows negligible QD655 signal consistent with lack of BBS-tag and therefore negligible channel surface density. (D) Compared to untreated HEK293 cells transiently expressing BBS-HERG 1a-YFP, pretreatment (≥1 h) with PA (1 mM) increased the surface density of hERG channels (~13%), while OA reduced (~20%, light gray column). Dotted line indicates 1. Numbers in parenthesis…

Figure 6. Simulated electrical activity of human atrial myocytes corresponding to LFD and HFD (with and without pacing) individuals. Action potential (A) and ICa,L (B), IK (C), IK1 (D), and IKur (E) current densities. Rapid atrial pacing caused more action potential shortening compared with HFD alone (blue trace), which was intermediate between LFD (black trace) and HFD + pacing (red trace).

Figure 7. Schematic representation of the effects of HFD and rapid pacing on atrial electrical properties in guinea pig heart. Short-term high-fat diet induced significant electrical remodeling of IK and ICa,L while IKur and IK1 remained unchanged compared to LFD controls. When HFD is combined with pacing IKur is significantly reduced while IK1 is increased in line with their roles in pathogenesis of supraventricular arrhythmias such as atrial fibrillation. The size of red arrows indicates change in the current densities of the ion channels.