Molecular diversify of the repolarizing voltage-gated K+ currents in mouse atrial cells

1. 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 (I-to,I-f), a rapidly activating, slowly inactivating current (I-K,I-s) and a non-inactivating, steady-state current (I-ss). The time- and voltage-dependent properties of I-to,I-f, I-K,I-s and I-ss in adult and P15 atrial cells are indistinguishable. 2. Pharmacological experiments reveal the presence of two components of I-K,I-s: one that is blocked selectively by 50 muM 4-aminopyridine (4-AP), and a 4-AP-insensitive component that is blocked by 25 mM TEA; I-ss is also partially attenuated by 25 mM TEA. There are also two components of I-K,I-s recovery from steady-state inactivation. 3. To explore the molecular correlates of mouse atrial I-K,I-s and I-ss, whole-cell voltage-clamp recordings were obtained from P15 and adult atrial cells isolated from transgenic mice expressing a mutant Kv2.1 alpha subunit (Kv2.1N216Flag) that functions as a dominant negative, and from P15 atrial myocytes exposed to (1 muM) antisense oligodeoxynucleotides (AsODNs) targeted against Kv1.5 or Kv2.1. 4. 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. 5. Analysis of the decay phases of the outward currents evoked during long (5 s)depolarizing voltage steps revealed that I-K,I-s is selectively attenuated in cells exposed to the Kv1.5 AsODN, whereas both I-K,I-s and I-ss are attenuated in the presence of the Kv2.1 AsODN. 6. In P15 and adult Kv2.1N216Flag-expressing atrial cells, mean +/-S.E.M. I-K,I-s and I-ss densities are also significantly lower than in non-transgenic atrial cells. In addition, pharmacological experiments reveal that the TEA-sensitive component I-K,I-s is selectively eliminated in P15 and adult Kv2.1N216Flag-expressing atrial cells. 7. Taken together, the results presented here reveal that both Kv1.5 and Kv2.1 contribute to mouse atrial I-K,I-s, consistent with the presence of two molecularly distinct components of I-K,I-s. In addition, Kv2.1 contributes to mouse atrial I-ss.