Altered State Dependence of C-Type Inactivation in the Long and Short Forms of Human Kv1.5

Abstract

Evidence from both human and murine cardiomyocytes suggests that truncated isoforms of Kv1.5 can be expressed in vivo. Using whole-cell patch-clamp recordings, we have characterized the activation and inactivation properties of Kv1.5ΔN209, a naturally occurring short form of human Kv1.5 that lacks roughly 75% of the T1 domain. When expressed in HEK 293 cells, this truncated channel exhibited a V1/2 of −19.5 ± 0.9 mV for activation and −35.7 ± 0.7 mV for inactivation, compared with a V1/2 of −11.2 ± 0.3 mV for activation and −0.9 ± 1.6 mV for inactivation in full-length Kv.15. Kv1.5ΔN209 channels exhibited several features rarely observed in voltage-gated K+ channels and absent in full-length Kv1.5, including a U-shaped voltage dependence of inactivation and “excessive cumulative inactivation,” in which a train of repetitive depolarizations resulted in greater inactivation than a continuous pulse. Kv1.5ΔN209 also exhibited a stronger voltage dependence to recovery from inactivation, with the time to half-recovery changing e-fold over 30 mV compared with 66 mV in full-length Kv1.5. During trains of human action potential voltage clamps, Kv1.5ΔN209 showed 30–35% greater accumulated inactivation than full-length Kv1.5. These results can be explained with a model based on an allosteric model of inactivation in Kv2.1 (Klemic, K.G., C.-C. Shieh, G.E. Kirsch, and S.W. Jones. 1998. Biophys. J. 74:1779–1789) in which an absence of the NH2 terminus results in accelerated inactivation from closed states relative to full-length Kv1.5. We suggest that differential expression of isoforms of Kv1.5 may contribute to K+ current diversity in human heart and many other tissues.

Amino-terminal Determinants of U-type Inactivation of Voltage-gated K+ Channels

“…1D), and a half-inactivation potential of Ϫ21.0 Ϯ 1.2 mV (Fig. 1E), which was consistent with previous studies from our laboratory and others (8,32). In the current study, we were particularly interested in the shape of the inactivation-voltage relationship, with FL Kv1.5 exhibiting a flat voltage dependence of inactivation at positive potentials (Fig.…”

“…Minor et al (31) hypothesized that point mutations within the T1 domain of Kv1.2 influence activation gating by altering the stability of channel closed states. Interestingly, kinetic modeling of inactivation in Shaker, Kv2.1, Kv3.1, and Kv1.5⌬N209 suggest that the apparent U-type voltage dependence of inactivation arises from accelerated inactivation from closed states of the channel (4,5,8). In our experiments, we observed that all of the T1 deletions (Kv1.5⌬N188, Kv1.5⌬N209, and Kv1.5T19ϩ163) and point mutations (Kv1.5AAQL) which impart U-type inactivation features to Kv1.5 also result in significant hyperpolarizing shifts of channel activation (Fig.…”

“…Interestingly, however, disruptions of the NH 2 termini of Kv channels can significantly affect the gating properties of the channel. A good example of this phenomenon is Kv1.5⌬N209, the naturally occurring short form of Kv1.5 comprising a deletion of greater than 80% of the cytosolic NH 2 terminus of Kv1.5, which exhibits activation and inactivation properties substantially different from the long-form of Kv1.5 (FL Kv1.5) (8). Throughout this study, we examined the voltage-dependent activation of Kv channels using the double pulse protocol described in Fig.…”

Short-Term Regulation of Information Processing at the Corticoaccumbens Synapse

“…Transcripts for these channels are detected in pyramidal neurons (Pan et al, 2004) and the NAc is labeled with a Kv1.5-specific antibody (Chung et al, 2000). However, homomeric Kv1.5 channels form functional, delayed rectifier K ϩ channels presenting a slowinactivating rate with poor cumulative properties (Coetzee et al, 1999;Kurata et al, 2001;Song, 2002). In a heterologous system, heteromeric assembly of Kv1.5 and Kv1.4 ␣ subunits forms functional channels expressing A-type-like inactivation and recovery from inactivation properties.…”

Dependence of 6β-acetoxy-7α-hydroxyroyleanone block of Kv1.2 channels on C-type inactivation

“…In some Kv isoforms (Kv1.4, Kv3.1, and Kv4.2), a fast inactivation takes place in which the cytoplasmic N-terminus acts as a ''ball-and-chain'', occluding the internal cavity of the opened Kv channel [5]. Almost all Kv channels display a slow type (also termed C-type) inactivation which often span seconds [6,7]. This C-type inactivation appears to involve destabilization of the outer channel pore surrounding the selectivity filter [8].…”