Heteromultimeric Kv1.2-Kv1.5 Channels Underlie 4-Aminopyridine-Sensitive Delayed Rectifier K ⁺ Current of Rabbit Vascular Myocytes

Abstract

Abstract-The molecular identity of vascular delayed rectifier K ϩ channels (K DR ) is poorly characterized. Inhibition by 4-aminopyridine (4-AP) of K DR of rabbit portal vein (RPV) myocytes was studied by patch clamp and compared with that of channels composed of Kv1.5 and/or Kv1.2 subunits cloned from the RPV and expressed in mammalian cells. 4-AP block of K DR was pulse-frequency dependent, required channel activation, and was associated with a positive shift in voltage dependence of activation. 4-AP caused a voltage-dependent reduction in mean open time of K DR . Relief of 4-AP block of whole cell currents during washout required channel activation and was unaffected by voltage. Homotetrameric Kv1.5 channels did not exhibit the shift in voltage dependence of activation exhibited by the native channels. In contrast, Kv1.2 channels displayed a shift in voltage dependence of activation, and this characteristic was also evident during 4-AP treatment when Kv1.2 was coexpressed with Kv1.5 or coupled to Kv1.5 in a tandem construct to produce heterotetrameric [Kv1.5/Kv1.2] 2 channels. K DR currents were not sensitive to charybdotoxin, which blocks homotetrameric Kv1.2 channels. The findings of this study (1) indicate that vascular K DR are inhibited by 4-AP via an open-state block mechanism and trapping of the drug within the pore on channel closure and (2) provide novel evidence based on a comparison of functional characteristics that indicate the dominant form of vascular K DR channel complex in RPV involves the heteromultimeric association of Kv1.2 and Kv1.5 subunits.

Molecular Composition of 4-Aminopyridine-Sensitive Voltage-Gated K + Channels of Vascular Smooth Muscle

“…4,5,8,9,11,24 This level of 4-AP sensitivity and the biophysical properties of the currents are consistent with those previously identified for Kv1-containing, 11,17,[22][23][24][25][26] but not Kv2-to 4-containing, 26 -31 Kv channels. The properties of whole-cell and unitary currents due to expression of Kv1.5 cloned from RPV closely mimicked those of native RPV K DR channels.…”

“…In the study by Kerr et al, 24 we present complementary evidence that whole-cell currents due to heteromultimeric, but not homomultimeric, channels composed of Kv1.2 and Kv1.5 possess functional identity with native 4-AP-sensitive K DR channels of RPV. 24 The combination of these observations provides compelling evidence that the dominant 4-AP-sensitive K DR channel complex of RPV vascular myocytes is a heteromultimer consisting of Kv1.2 and Kv1.5 subunits. This study provides novel insights into vascular Kv channel subunit composition.…”

“…This subunit association may be predicted to produce channels that possess functional properties that are distinct from homomultimeric channels, an issue that is addressed in the study by Kerr et al 24 The molecular biological, biochemical, and immunocytochemical data presented in this study indicate that Kv1.2 and Kv1.5 are the only delayed rectifier-type Kv1␣ pore-forming subunits expressed by RPV myocytes and that these subunits associate to form heteromultimeric Kv channels. In the study by Kerr et al, 24 we present complementary evidence that whole-cell currents due to heteromultimeric, but not homomultimeric, channels composed of Kv1.2 and Kv1.5 possess functional identity with native 4-AP-sensitive K DR channels of RPV. 24 The combination of these observations provides compelling evidence that the dominant 4-AP-sensitive K DR channel complex of RPV vascular myocytes is a heteromultimer consisting of Kv1.2 and Kv1.5 subunits.…”

“…The properties of whole-cell and unitary currents due to expression of Kv1.5 cloned from RPV closely mimicked those of native RPV K DR channels. 11 However, homomultimeric Kv1.5 channels do not share functional identity with vascular K DR because (1) differences in rate and voltage dependence of inactivation are apparent 11 ; (2) RPV Kv1.5 channels in inside-out membrane patches of mouse L cells or human embryonic kidney 293 (HEK) cells do not exhibit modulation by purified protein kinase A in the presence of ATP 32 ; and (3) 4-AP treatment is associated with a positive shift in the voltage dependence of activation of native K DR , but not Kv1.5 channels, as described in another study published in this issue of Circulation Research by Kerr et al 24 This lack of functional identity indicates that Kv1.5 cannot be the only Kv1 subunit contributing to K DR channels of vascular myocytes.…”

Long Noncoding RNA Kcna2 Antisense RNA Contributes to Ventricular Arrhythmias via Silencing Kcna2 in Rats With Congestive Heart Failure

“…Moreover, Kcna2 channels have been shown to play a pivotal role in maintaining the resting membrane potential and, consequently, regulating cellular excitability in neurons 28. There is direct evidence showing that the I Ks is generated by Kcna2 in Xenopus oocytes, rabbit vascular myocytes, pulmonary arterial smooth muscle cells, rat mesenteric artery smooth muscle cells, and canine colonic circular smooth muscles 29, 30, 31, 32, 33. Specifically, Kcna2 was demonstrated to contribute to the I Ks, rather than the transient outward potassium current, in adult rat myocytes 8.…”