XB-IMG-138289
Xenbase Image ID: 138289
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Figure 2. Xenopus Kv2.1 and Kv2.2 mRNAs induce expression of delayed rectifier-type potassium currents in Xenopus oocytes. For A-C, currents were
generated in response to 60 msec voltage steps to potentials ranging from -50 to + 100 mV from a holding potential of -80 mV; leak-subtracted currents.
are shown (see Materials and Methods). A, Kv2.1 mRNA induces expression of delayed rectifier-type potassium currents in Xenopus oocytes. The average
current size at +20 mV is 1.1 -t 0.6 FA (mean t- SD; n = 7) for 1.7 ng of injected cRNA. B, Kv2.2 mRNA-induced current is sustained for the duration
of the depolarizing pulse. The average current size at +20 mV is 1.3 -t 0.3 PA (mean t- SD; n = 6) for 1 ng of injected cRNA. C, Comparison of the
kinetics of activation of Kv2.1 and Kv2.2 mRNA-induced currents. Current traces from A and B were superimposed for comparison. The Kv2.1
mRNA-induced current (dotted line) rises faster than the Kv2.2 mRNA-induced current (solid line). D, Tail current analysis indicates the Kv2.1
mRNA-induced channels are potassium-selective. Currents were activated with prepulses of 100 msec duration to +25 mV, then stepped to different
hyperpolarizing pulses ranging from -100 to 10 mV (inset). Varying the external K+ concentration shifts the reversal potential as predicted by the Nernst
equation for a K+-selective channel. Results from a representative experiment are shown, and average results are indicated in the text. E, Sensitivity of
Kv2.1 and Kv2.2 currents to TEA. Current amplitude was measured in the presence of variable concentrations of TEA. Current amplitude was plotted
against TEA concentration. Current values + SEM were taken from voltage pulses to +20 mV. F, Normalized conductance versus voltage relationships
for Xenopus Kv2.1, Kv2.2, Kvl.1, and Kv1.2 mRNA-induced currents. The conductance was calculated for a given voltage command (v) and its
corresponding steady-state current response (0 from the formula G = 1/(V - EK), where the equilibrium potential for Kt (EK) is -116 mV. Half-maximal
activation (V,,,) is achieved at values of +25.0 2 0.1 mV (mean 5 SD; II = 7) for Kv2.1 currents and at +30.0 + 5.5 mV (mean + SD; n = 3) for Kv2.2
currents. Kvl currents activate and achieve G,,, at less positive membrane potentials than do the Kv2 currents. Data from representative recordings were
used to generate the graphs. Single Boltzmann distributions fit Kvl.1 and Kv1.2 data well (Jones and Ribera, 1994) (A. Ribera, unpublished observations),
whereas Kv2.1 and Kv2.2 data deviate consistently from the Boltzmann isotherm (data not shown). This type of behavior has been observed previously
in human Kv2.1 channels expressed in oocytes (Benndorf et al., 1994). Image published in: Burger C and Ribera AB (1996) Copyright © 1996. This image is reproduced with permission of the publisher and the copyright holder. This is an Open Access article distributed under the terms of the Creative Commons Attribution License. Larger Image Printer Friendly View |