Role of the S2 and S3 Segment in Determining the Activation Kinetics in Kv2.1 Channels |
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Authors: | R Koopmann A Scholle J Ludwig T Leicher T Zimmer O Pongs K Benndorf |
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Institution: | Institut für Physiologie, Herz-Kreislauf-Physiologie, Friedrich-Schiller-Universit?t, 07740 Jena, Germany, DE Zentrum für Molekulare Neurobiologie, Institut für Neurale Signalverarbeitung, UKE (Haus 42), Martinistr. 52, 20251 Hamburg, Germany, DE
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Abstract: | We constructed chimeras between the rapidly activating Kv1.2 channel and the slowly activating Kv2.1 channel in order to
study to what extent sequence differences within the S1–S4 region contribute to the difference in activation kinetics. The
channels were expressed in Xenopus oocytes and the currents were measured with a two-microelectrode voltage-clamp technique. Substitution of the S1–S4 region
of Kv2.1 subunits by the ones of Kv1.2 resulted in chimeric channels which activated more rapidly than Kv2.1. Furthermore,
activation kinetics were nearly voltage-independent in contrast to the pronounced voltage-dependent activation kinetics of
both parent channels. Systematic screening of the S1–S4 region by the replacement of smaller protein parts resolved that the
main functional changes generated by the S1–S4 substitution were generated by the S2 and the S3 segment. However, the effects
of these segments were different: The S3 substitution reduced the effective gating charge and accelerated both a voltage-dependent
and a voltage-independent component of the activation time course. In contrast, the S2 substitution accelerated predominantly
the voltage-dependent component of the activation time course thereby leaving the effective gating charge unchanged. It is
concluded that the S2 and the S3 segment determine the activation kinetics in a specific manner.
Received: 13 November 2000/Revised: 5 April 2001 |
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Keywords: | : Kv2 1 and Kv1 2 channels — Activation time course — Voltage dependence — S2 and S3 transmembrane segments |
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