Dissection of the voltage-activated potassium outward currents in adult mouse ventricular myocytes: I to,f, I to,s, I K,slow1, I K,slow2, and I ss

Abstract

Voltage-activated outward K(+) currents (I (Kv)) are essential for cardiac repolarization and are major factors in the electrophysiological remodeling and arrhythmias seen in heart disease. Mouse models have been useful for understanding cardiac electrophysiology. However, previous methods for separating and quantifying the components of I (Kv) in mouse myocardium have yielded inconsistencies. In this study, we developed a statistically rigorous method to uniquely quantify various I (Kv) in adult mouse ventricular myocytes, and concluded that tri-exponential functions combined with depolarizing pulses of duration greater than 20 s are essential to adequately separate the different I (Kv) components. This method enabled us to reliably dissect the kinetic components of the decay phase of I (Kv) into fast (I (to)), intermediate (K(V)1.5-encoded I (K,slow1)) and slow (K(V)2-encoded I (K,slow2)) components. The most rapid kinetic phase, I (to), can be further dissected into fast (K(V)4-encoded I (to,f)) and slow (K(V)1.4-encoded I (to,s)) components by measuring recovery from inactivation, voltage-dependence of activation and sensitivity to HpTx-2 and 4-AP. The applicability of our dissection method was validated using transgenic mice over-expressing dominant-negative K(V)1.1 transgene which largely abolished the 4-AP-sensitive portion of I (to) (i.e., I (to,s)) and the I (K,slow1) component. We also applied our method to Irx5-deficient mice and verified selective elevations of I (to) in endocardial myocytes. Our method should prove useful in future electrophysiological studies using mouse.

Reduction in Kv Current Enhances the Temporal Dispersion of the Action Potential in Diabetic Myocytes: Insights From a Novel Repolarization Algorithm

“…In the attempt to define the role of diminished outward Kv currents on the prolongation of AP and enhanced beat‐to‐beat variability observed in diabetic myocytes, outward K + currents in control mouse myocytes were inhibited with 4‐AP (0.1 mmol/L) 32, 33, 34, 35. This pharmacological intervention led to a prolongation of AP comprising 95% of the whole repolarization, with a maximum of 5.3‐fold increase in duration at 15.6% of the repolarization (Figure 9A and 9B).…”

“…To test the effects of inhibition of Kv currents, APs were continuously recorded for the same cells before and after exposure to 4‐aminopyridine (4‐AP; 0.1 mmol/L) 30, 32, 33, 34, 35. At this concentration level, 4‐AP has been previously reported to abolish the large, slowly inactivating phase of the Kv‐based I K,slow 32, 34, 35 leading to prolongation of AP 33. To test the acute effects of high glucose, APs were continuously recorded for the same cells before and after exposure to a Tyrode solution containing 20 mmol/L of glucose.…”

Iroquois Homeodomain Transcription Factors in Heart Development and Function

“…75 The I to,f gradient in rodent ventricles is linked with gradients in K V 4.2 expression across the ventricular wall, 16,20,76,77 which are abolished in Irx5 KO hearts as a result of selective increases in I to,f and K V 4.2 along with action potential duration abbreviation in ENDO myocardium ( Figure 5A). 16,78 The inverse relationship between Irx5 and K V 4.2 expression suggest that Irx5 determines the repolarization properties in mice by acting as a repressor of K V 4.2 expression. Notably, similar to other Irx proteins, 21,25,79 Irx5 can act as either an activator or repressor in a context-dependent manner.…”

The Role of Proinflammatory Cytokines in Regulation of Cardiac Bioelectrical Activity: Link to Mechanoelectrical Feedback

“…TNF-α-induced alternation of I Kur was investigated only in mice. As shown previously, ultrarapid K + current (also called I K,slow1 ) is present in adult mice ventricular myocardium (Liu et al, 2011;Brouillette et al, 2004).…”