Modulation of Closed-State Inactivation in Kv2.1/Kv6.4 Heterotetramers as Mechanism for 4-AP Induced Potentiation.
The voltage-gated K+ (Kv) channel subunits Kv2.1 and Kv2.2 are expressed in almost every tissue. The diversity of Kv2 current is increased by interacting with the electrically silent Kv (KvS) subunits Kv5-Kv6 and Kv8-Kv9, into functional heterotetrameric Kv2/KvS channels. These Kv2/KvS channels possess unique biophysical properties and display a more tissue-specific expression pattern, making them more desirable pharmacological and therapeutic targets. However, little is known about the pharmacological properties of these heterotetrameric complexes. We demonstrate that Kv5.1, Kv8.1 and Kv9.3 currents were inhibited differently by the channel blocker 4-aminopyridine (4-AP) compared to Kv2.1 homotetramers. In contrast, Kv6.4 currents were potentiated by 4-AP while displaying moderately increased affinities for the channel pore blockers quinidine and flecainide. We found that the 4-AP induced potentiation of Kv6.4 currents was caused by modulation of the Kv6.4-mediated closed-state inactivation: suppression by 4-AP of the Kv2.1/Kv6.4 closed-state inactivation recovered a population of Kv2.1/Kv6.4 channels that was inactivated at resting conditions, i.e. at a holding potential of -80 mV. This modulation also resulted in a slower initiation and faster recovery from closed-state inactivation. Using chimeric substitutions between Kv6.4 and Kv9.3 subunits, we demonstrated that the lower half of the S6 domain (S6c) plays a crucial role in the 4-AP induced potentiation. These results demonstrate that KvS subunits modify the pharmacological response of Kv2 subunits when assembled in heterotetramers and illustrate the potential of KvS subunits to provide unique pharmacological properties to the heterotetramers, as is the case for 4-AP on Kv2.1/Kv6.4 channels.
Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium.
Jeroen I
JI
Stas
Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium.
Elke
E
Bocksteins
Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium.
Alain J
AJ
Labro
Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium.
Dirk J
DJ
Snyders
D015761:4-Aminopyridine / Q000737:chemistry* / Q000494:pharmacology; D020816:Amino Acid Motifs / Q000235:genetics; D000818:Animals; D002460:Cell Line; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics; D024642:Potassium Channels, Voltage-Gated / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics; D011392:Proline / Q000737:chemistry; D055503:Protein Multimerization / Q000187:drug effects*; D021122:Protein Subunits / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics; D051669:Shab Potassium Channels / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics; D014162:Transfection
C496988:KCNB1 protein, human; C109966:KCNF1 protein, human; C120777:KCNV1 protein, human; D009419:Nerve Tissue Proteins; D024642:Potassium Channels, Voltage-Gated; D021122:Protein Subunits; D051669:Shab Potassium Channels; D011392:Proline; D015761:4-Aminopyridine