Characterization of a voltage-gated K+ channel beta subunit expressed in human heart.

Abstract

Voltage-gated K+ channels are important modulators of the cardiac action potential. However, the correlation of endogenous myocyte currents with K+ channels cloned from human heart is complicated by the possibility that heterotetrameric av-subunit combinations and functionaltering .8 subunits exist in native tissue. Therefore, a variety of subunit interactions may generate cardiac K+ channel diversity. We report here the cloning of a voltage-gated K+ channel 13 subunit, hK4,83, from adult human left ventricle that shows 84% and 74% amino acid sequence identity with the previously cloned rat Kv31 and Kv32 subunits, respectively.Together these three KvI3 subunits share >82% identity in the carboxyl-terminal 329 aa and show low identity in the aminoterminal 79 aa. RNA analysis indicated that hKv.I3 message is 2-fold more abundant in human ventricle than in atrium and is expressed in both healthy and diseased human hearts.Coinjection of hKv483 with a human cardiac delayed rectifier, hKv1.5, in'Xenopus oocytes increased inactivation, induced an 18-mV hyperpolarizing shift in the activation curve, and slowed deactivation (T = 8.0 msec vs. 35.4 msec at -50 mV).hKvI33 was localized to human chromosome 3 by using a human/rodent cell hybrid mapping panel. These data confirm the presence of functionally important K+ channel 13 subunits in human heart and indicate that 18-subunit composition must be accounted for when comparing cloned channels with endogenous cardiac currents.Potassium channels play an essential role in most excitable cells and are responsible for many diverse physiological functions (1-3). In the heart, voltage-gated K+ channels (Kvs) are responsible for establishing the resting membrane potential and modulating the frequency and duration of action potentials, as well as being the targets of several antiarrhythmic drugs. At present, whole-cell and patch-clamp studies have characterized at least five distinct K+ currents in mammalian myocardium (4-14), while molecular cloning efforts have yielded at least seven cardiac K+ channel genes expressed in rat or human heart (15-18). Six of these cloned genes represent Shaker-like K+ channels from either the K1, KV2, or K,4 gene subfamilies. The diversity of K+ channels in the heart is readily apparent. Nevertheless, correlation of cloned channels with endogenous myocyte currents has been difficult because most heterologously expressed channels display either a fastinactivating or a delayed-rectifier-type current, often with similar pharmacology. Although the human K,1.5 isoform (hK,1. We report here the cloning and characterization of a cDNA from human heart that encodes another K+ channel , subunit, designated hKV,33, adopting proposed nomenclature (26). ¶ This subunit is present in both healthy and cardiomyopathic heart tissue and alters the functional properties of hKvl.5, converting it from a delayed rectifier to a channel with rapid, but partial, inactivation. In addition, this current activates at lower voltages and has dramatically slower deactivati...

Molecular and functional characterization of a rat brain Kvβ3 potassium channel subunit

“…The digit following the period was introduced to distinguish K,fl subunits which only differ in their N-terminal structure. Note that the homologues of rK,fl1.2 from human and ferret heart were in the original publications called hK,fl3 [9,10] or fKvfl3 [11]. respectively.…”

“…1 which show sequence identity to rK,fll. 1 starting from amino-acid residue Y73 were cloned from human and ferret heart [9][10][11]; their N-terminal ends, however, are quite different. Morales et al [11] described PCR cloning of a homologue to the clone from ferret using a rat library.…”

“…rK,fll from rat brain [6] therefore becomes now rKvfll. 1, the rat homologue to the fl-subunits from human and ferret heart which were in the original publications called hK,fl3 [9,10] or fK~3 [11] becomes rKvfll.2. According to this notation, the subunits from human and ferret heart should therefore be named hK~,81.2 and fK~fll.2, respectively.…”

Mutations in the Kvβ2 Binding Site for NADPH and Their Effects on Kv1.4

“…Channels in the Kv1 subfamily consist of hetero-oligomeric protein complexes comprising four pore-forming ␣ subunits in permanent association with four modulatory ␤ subunits (1). Three different Kv␤ subunit genes (␤1, ␤2, and ␤3) have been cloned from different tissues in several species (2)(3)(4)(5)(6). Kv␤ subunits coassemble with Kv␣ subunits in the endoplasmic reticulum and enhance biosynthesis, maturation, and surface expression of voltage-gated K ϩ channel complexes.…”

The molecular basis for the actions of KVβ1.2 on the opening and closing of the KV1.2 delayed rectifier channel

“…[1][2][3][4][5][6][7][8] According to recent crystallographic studies, these are positioned below the associated channels in 1:1 stoichiometry with four-fold symmetry and form a so-called 'hanging gondola'. 9,10 To date, three mammalian K V β genes (K V β1-3) have been cloned, [11][12][13][14][15][16] as well as a K V β homolog from Drosophila melanogaster called Hyperkinetic, 17 and these can be considered as two distinct regions based on primary sequence and function. The C-terminus is highly conserved among the three K V β genes and co-translationally forms the primary contacts with the T1 domain of the N-terminus of K V α1 subunits.…”