Functional differences of a Kv2.1 channel and a Kv2.1/Kv1.2S4-chimera are confined to a concerted voltage shift of various gating parameters.
When expressed in Xenopus oocytes, the voltage-dependent K+ channels Kv1.2 and Kv2.1 have similar steady state parameters of activation but the kinetics of activation is significantly faster in the Kv1.2 channels. Activation results from intramolecular arrangements which start with the movement of the voltage sensor and end with the opening of the pore. The S4-segment and the H5-loop comprise at least part of the respective involved structural elements. The molecular mechanism of coupling between sensing of voltage and opening of the pore is less well understood. We have measured whole cell and single channel ionic currents in the rapidly activating Kv1.2 channel of the rat, the slowly activating Kv2.1 channel of the human, and in an S4-chimera Kv2.1/Kv1.2S4. With respect to the Kv2.1 channel, steady state activation and steady state C-type inactivation of the chimeric channel are shifted by more than 50 mV in the depolarizing direction. The property of rapid activation in Kv1.2 channels was not transferred to the Kv2.1 channels with the transplanted S4-region. Instead, the kinetics of activation, deactivation, and recovery from C-type inactivation as well as the voltage sensitivity of the 4-aminopyridine block are similar to the corresponding processes in Kv2.1 channels if they are related to the steady state activation and inactivation, respectively. The unitary current and the mean open time of single channel openings of the S4-chimeric channels resemble the respective values of Kv2.1 channels. It is concluded that the insertion of the S4-segment of Kv1.2 channels into Kv2.1 channels modifies the gating at the early steps of activation leaving all properties associated with the open state(s) of the Kv2.1 channels unaffected.
Koopmann
R
R
Zentrum für Physiologie, Universität zu Köln, Germany.
Benndorf
K
K
Lorra
C
C
Pongs
O
O
D015761:4-Aminopyridine / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D017931:DNA Primers; D004594:Electrophysiology; D015870:Gene Expression; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D007700:Kinetics; D008845:Microinjections; D008969:Molecular Sequence Data; D009865:Oocytes; D018408:Patch-Clamp Techniques; D016133:Polymerase Chain Reaction; D015221:Potassium Channels / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014981:Xenopus
D017931:DNA Primers; D015221:Potassium Channels; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D015761:4-Aminopyridine