Genetic ablation or pharmacological inhibition of Kv1.1 potassium channel subunits impairs atrial repolarization in mice

Abstract

Voltage-gated Kv1.1 potassium channel α-subunits, encoded by the Kcna1 gene, have traditionally been regarded as neural-specific with no expression or function in the heart. However, recent data revealed that Kv1.1 subunits are expressed in atria where they may have an overlooked role in controlling repolarization and arrhythmia susceptibility independent of the nervous system. To explore this concept in more detail and to identify functional and molecular effects of Kv1.1 channel impairment in the heart, atrial cardiomyocyte patch-clamp electrophysiology and gene expression analyses were performed using Kcna1 knockout ( Kcna1^-/-) mice. Specifically, we hypothesized that Kv1.1 subunits contribute to outward repolarizing K⁺ currents in mouse atria and that their absence prolongs cardiac action potentials. In voltage-clamp experiments, dendrotoxin-K (DTX-K), a Kv1.1-specific inhibitor, significantly reduced peak outward K⁺ currents in wild-type (WT) atrial cells but not Kcna1^-/- cells, demonstrating an important contribution by Kv1.1-containing channels to mouse atrial repolarizing currents. In current-clamp recordings, Kcna1^-/- atrial myocytes exhibited significant action potential prolongation which was exacerbated in right atria, effects that were partially recapitulated in WT cells by application of DTX-K. Quantitative RT-PCR measurements showed mRNA expression remodeling in Kcna1^-/- atria for several ion channel genes that contribute to the atrial action potential including the Kcna5, Kcnh2, and Kcnj2 potassium channel genes and the Scn5a sodium channel gene. This study demonstrates a previously undescribed heart-intrinsic role for Kv1.1 subunits in mediating atrial repolarization, thereby adding a new member to the already diverse collection of known K⁺ channels in the heart.

Keywords: Kv1.1; action potential; atria; channel remodeling; dendrotoxin-K.

Fig. 1.

Dendrotoxin-K (DTX-K) reduced outward K⁺ currents in wild-type (WT) mouse atrial myocytes. A–C: representative raw current traces in a WT cell in response to 1-s depolarizing voltage steps of +10 mV from a holding potential of −50 mV to +70 mV: at baseline (A); with application of 10 nM DTX-K (B); and following subtraction of the current difference to isolate the DTX-K-sensitive component (C). D: quantification of the peak current densities before (control) and after (DTX-K) application of DTX-K in WT atrial myocytes. The dotted line in the traces indicates 0 pA. Sample numbers (n) indicate myocytes per mouse. *P ≤ 0.05 (2-tailed paired Student’s t-test).

Fig. 2.

Dendrotoxin-K (DTX-K) had no significant effect on outward K⁺ currents in Kcna1^−/− atrial myocytes. A–C: representative raw current traces in a Kcna1^−/− cell in response to 1-s depolarizing voltage steps of +10 mV from a holding potential of −50 mV to +70 mV: at baseline (A); with application of 10 nM DTX-K (B); and following subtraction of the current difference to isolate the DTX-K-sensitive component (C). D: quantification of the peak current densities before (control) and after (DTX-K) application of DTX-K in Kcna1^−/− atrial myocytes. The dotted line in the traces indicates 0 pA. Sample numbers (n) indicate myocytes per mouse.

Fig. 3.

Kcna1^−/− atrial myocytes exhibit action potential duration (APD) prolongation. A: representative atrial action potentials recorded in a wild-type (WT) cell and a Kcna1^−/− cell. The resting membrane potential is indicated next to each waveform. B: average APD in WT and Kcna1^−/− cells at 30, 50, and 90% repolarization (APD₃₀, APD₅₀, and APD₉₀). C and D: average resting membrane potential (C) and action potential amplitude (D) in WT (n = 29/16) and Kcna1^−/− cells (n = 19/10). Sample numbers (n) indicate myocytes per mouse. *P ≤ 0.05; ****P ≤ 0.0001 (2-tailed unpaired Student’s t-test). KO, knockout.

Fig. 4.

Dendrotoxin-K (DTX-K) prolongs action potentials in wild-type (WT) atrial myocytes. A: a representative action potential recording in a WT cell at baseline (black line; labeled control) overlaid with the resulting action potential after application of 10 nM DTX-K (red line; labeled DTX-K). B: average action potential duration (APD) in WT cells at 30, 50, and 90% repolarization (APD₃₀, APD₅₀, and APD₉₀) before (control) and after (DTX-K) application of 10 nM DTX-K. C: a representative action potential recording in a Kcna1^−/− cell at baseline (black line; labeled control) overlaid with the resulting action potential after application of 10 nM DTX-K (red line; labeled DTX-K). D: average APD in Kcna1^−/− cells at APD₃₀, APD₅₀, and APD₉₀ before (control) and after (DTX-K) application of 10 nM DTX-K. The resting membrane potential before and after DTX-K is indicated next to each waveform. Sample numbers (n) indicate myocytes per mouse. ***P ≤ 0.001 (2-tailed paired Student’s t-test).

Fig. 5.

Action potential prolongation in Kcna1^−/− cardiomyocytes is exacerbated in right atria. A–D: representative action potential recordings before (black line; labeled control) and after (red line; labeled DTX-K) application of 10 nM DTX-K in wild-type (WT) cells from left (A) and right atria (B) and in Kcna1^−/− cells from left (C) and right atria (D).

Fig. 6.

Kcna1^−/− atria exhibit evidence of ion channel gene expression remodeling. qPCR was used to measure relative differences in atrial mRNA levels of the primary cardiac ion channel α-subunit genes associated with the atrial action potential, as well as the main Kv1-associated β-subunit genes (n = 6 per genotype). *P ≤ 0.05; **P ≤ 0.01 (2-tailed unpaired Student’s t-test). KO, knockout; WT, wild type.