Molecular diversity of the repolarizing voltage‐gated K⁺ currents in mouse atrial cells

Abstract

Voltage‐clamp studies on atrial myocytes isolated from adult and postnatal day 15 (P15) C57BL6 mice demonstrate the presence of three kinetically distinct Ca2+‐independent, depolarization‐activated outward K+ currents: a fast, transient outward current (Ito,f), a rapidly activating, slowly inactivating current (IK,s) and a non‐inactivating, steady‐state current (Iss). The time‐ and voltage‐dependent properties of Ito,f, IK,s and Iss in adult and P15 atrial cells are indistinguishable. Pharmacological experiments reveal the presence of two components of IK,s: one that is blocked selectively by 50 μM 4‐aminopyridine (4‐AP), and a 4‐AP‐insensitive component that is blocked by 25 mM TEA; Iss is also partially attenuated by 25 mM TEA. There are also two components of IK,s recovery from steady‐state inactivation. To explore the molecular correlates of mouse atrial IK,s and Iss, whole‐cell voltage‐clamp recordings were obtained from P15 and adult atrial cells isolated from transgenic mice expressing a mutant Kv2.1 α subunit (Kv2.1N216Flag) that functions as a dominant negative, and from P15 atrial myocytes exposed to (1 μM) antisense oligodeoxynucleotides (AsODNs) targeted against Kv1.5 or Kv2.1. Peak outward K+ current densities are attenuated significantly in atrial myocytes isolated from P15 and adult Kv2.1N216Flag‐expressing animals and in P15 cells exposed to AsODNs targeted against either Kv1.5 or Kv2.1. Analysis of the decay phases of the outward currents evoked during long (5 s) depolarizing voltage steps revealed that IK,s is selectively attenuated in cells exposed to the Kv1.5 AsODN, whereas both IK,s and Iss are attenuated in the presence of the Kv2.1 AsODN. In P15 and adult Kv2.1N216Flag‐expressing atrial cells, mean ± s.e.m. IK,s and Iss densities are also significantly lower than in non‐transgenic atrial cells. In addition, pharmacological experiments reveal that the TEA‐sensitive component IK,s is selectively eliminated in P15 and adult Kv2.1N216Flag‐expressing atrial cells. Taken together, the results presented here reveal that both Kv1.5 and Kv2.1 contribute to mouse atrial IK,s, consistent with the presence of two molecularly distinct components of IK,s. In addition, Kv2.1 contributes to mouse atrial Iss.

Molecular Identification and Functional Roles of a Ca2+-activated K+ Channel in Human and Mouse Hearts

“…Close examination of the data shows significant differences in the AP duration in the mouse atrial and ventricular myocytes. This is most likely due to a smaller K ϩ current density in atrial cells compared with ventricular cells, which has been described previously (18,19).…”

“…These currents have been classified into two broad categories: 1) rapidly activating and inactivating transient outward K ϩ currents, I to and 2) slowly or non-inactivating K ϩ currents, typically referred to as I K . In adult mouse atrial myocytes, at least three kinetically distinct components of Ca 2ϩ -independent depolarization-activated K ϩ currents have been documented: a fast, transient outward current, I to,f , a rapidly activating, slowly inactivating current, I K,s , and a noninactivating, steady-state current, I ss (18). It has been demonstrated that K v 4 ␣ subunits underlie mouse atrial and ventricular I to,f (29).…”

“…It has been demonstrated that K v 4 ␣ subunits underlie mouse atrial and ventricular I to,f (29). In addition, ␣ subunits of both K v 1.5 and K v 2.1 contribute to the generation of I K,s in mouse atrial and ventricular myocytes (30,31) and that K v 2.1 also contributes to mouse atrial I ss (18).…”

“…Ca 2ϩ Dependence of the Apamin-sensitive Currents-To further document the presence of I K,Ca in cardiac myocytes, wholecell current was recorded using voltage steps from a holding potential of Ϫ55 mV to inactivate the transient outward K ϩ currents, which were known to be present in mouse atrial and ventricular myocytes (18,19) (Fig. 2).…”

Effects of hyperthyroidism on delayed rectifier K+ currents in left and right murine atria

“…Also, the amplitude of I Kur was determined by the fitting of two exponentials to the 6-s step from Ϫ50 to ϩ20 mV (Clampex; Axon Instruments). The first exponential time constant represents the inactivation of Ito, whereas the second exponential is believed to represent the inactivation of I Kur (5). The amplitudes associated with the second exponential time constant were analyzed as representing a fairly pure measure of IKur.…”