Abstract

The three members of the ether-à-go-go-gene-like (Elk; Kv12.1-Kv12.3) family of voltage-gated K+ channels are predominantly expressed in neurons, but only little information is available on their physiological relevance. It was shown that Kv12.2 channels modulate excitability of hippocampal neurons, but no native current could be attributed to Kv12.1 and Kv12.3 subunits yet. This may appear somewhat surprising, given high expression of their mRNA transcripts in several brain areas. Native Kv12 currents may have been overlooked so far due to limited knowledge on their biophysical properties and lack of specific pharmacology. Except for Kv12.2, appropriate genetically modified mouse models have not been described; therefore, identification of Kv12-mediated currents in native cell types must rely on characterization of unique properties of the channels. We focused on recombinant human Kv12.1 to identify distinct properties of these channels. We found that Kv12.1 channels exhibited significant mode shift of activation, i.e., stabilization of the voltage sensor domain in a “relaxed” open state after prolonged channel activation. This mode shift manifested by a slowing of deactivation and, most prominently, a significant shift of voltage dependence to hyperpolarized potentials. In contrast to related Kv11.1, mode shift was not sensitive to extracellular Na+, which allowed for discrimination between these isoforms. Sensitivity of Kv12.1 and Kv11.1 to the broad-spectrum K+ antagonist 4-aminopyridine was similar. However, 4-AP strongly activated Kv12.1 channels, but it was an inhibitor of Kv11 channels. Interestingly, the agonist of Kv11 channels NS1643 also differentially modulated the activity of these channels, i.e., NS1643 activated Kv11.1, but strongly inhibited Kv12.1 channels. Thus, these closely related channels are distinguished by inverse pharmacological profiles. In summary, we identified unique biophysical and pharmacological properties of Kv12.1 channels and established straightforward experimental protocols to characterize Kv12.1-mediated currents. Identification of currents in native cell types with mode shift that are activated through 4-AP and inhibited by NS1643 can provide strong evidence for contribution of Kv12.1 to whole cell currents.

Highlights

  • The ether-à-go-go (Eag) superfamily of voltage-gated K+ channels comprises three evolutionary conserved families that share high sequence homology: Ether-à-go-go (Eag; Kv10), etherà-go-go-related-gene (Erg; Kv11) and ether-à-go-go-gene-like (Elk; Kv12) channels (Bauer and Schwarz, 2001)

  • Our results suggested that voltage-clamp protocols designed to detect mode shift in combination with pharmacology using 4AP or NS1643 should provide a robust approach for isolation of Kv12.1-mediated currents in native cell types

  • We found that mode shift of human Kv12.1 was readily induced by depolarized holding potentials between −60 and 0.1 mV (0 mV) and that it manifested by slowed channel deactivation and a striking shift of voltage dependence to hyperpolarized potentials

Read more

Summary

Introduction

The ether-à-go-go (Eag) superfamily of voltage-gated K+ channels comprises three evolutionary conserved families that share high sequence homology: Ether-à-go-go (Eag; Kv10), etherà-go-go-related-gene (Erg; Kv11) and ether-à-go-go-gene-like (Elk; Kv12) channels (Bauer and Schwarz, 2001). The beststudied member, Kv11.1 (the human isoform is referred to as HERG channel) mediates rapidly activating K+ current IKr in cardiac myocytes determining heart action potential duration (Sanguinetti et al, 1995). Loss of Kv11.1 channel function through mutations or drug treatment causes cardiac arrhythmia and sudden death in humans (Curran et al, 1995; Sanguinetti et al, 1995; Trudeau et al, 1995). Kv11 channels mediate important K+ currents in neurons of the auditory brainstem (Hardman and Forsythe, 2009), the olfactory bulb (Hirdes et al, 2009) and the midbrain (Ji et al, 2012). Kv10.1 channel mutations cause developmental disorders and epilepsy (Kortum et al, 2015; Simons et al, 2015)

Methods
Results
Discussion
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call