Role of the S2 and S3 Segment in Determining the Activation Kinetics in Kv2.1 Channels

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.

Functional Analysis of Kv1.2 and Paddle Chimera Kv Channels in Planar Lipid Bilayers

“…The ‘normally functioning’ Kv1.2 channels in this study are actually quite dramatically different in many respects from Kv1.2 channels reported in the literature, expressed in Xenopus oocytes28. For example, the activation midpoint of Kv1.2 is −72 mV in the present study and −3.5 mV in oocytes28.…”

“…For example, the activation midpoint of Kv1.2 is −72 mV in the present study and −3.5 mV in oocytes28. The rate of activation in oocytes is slow compared to the present study to the extent that the currents are unrecognizable as being carried by the same channels.…”

Delayed Rectifier and A-Type Potassium Channels Associated with Kv 2.1 and Kv 4.3 Expression in Embryonic Rat Neural Progenitor Cells

“…Activation time constants were estimated for each type by fitting an exponential curve to the rising phase; the two values, 1.69±0.04 and 1.03±0.13 ms for the delayed rectifier and the A-type, respectively, differ significantly (0.01 level). The delayed rectifier activation is considerably faster than in Kv 2.1 channels expressed in oocytes [19] , but the A-type time constant is close to the value measured in expressed Kv 4.3 [20] .…”

Characterization of chromanol 293B-induced block of the delayed-rectifier K+ current in heart-derived H9c2 cells

“…Previous studies have demonstrated that the S3 segment of Kv2.1 channels could be important in determining the gating change and the activation kinetics of these channels (Koopmann et al, 2001;Li-Smerin and Swartz, 2001). In our study, chromanol 293B not simply altered the activation time course of I K ; however, it also produced a decrease in the effective gating charge.…”