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Figure 2.11 M-type K+ currents: from voltage-clamp to 'current-clamp'. Recordings from frog sympathetic neurons. Upper traces in each record show currents (I), lower traces show voltage K). (a) Voltage-clamp records showing membrane currents evoked by 0.5-s voltage steps from holding potentials of — 90 mV (left), where KM channels are shut, and —■46 mV (right), where KM channels are open. (b) Voltage responses to 1-s current injections at the same two potentials observed when the voltage-clamp circuit is switched off. Note that the effect of activating the current is to severely reduce the voltage response to current injection. (Adapted from Fig. 6 in Brown, DA (1988) Ion Channels, Vol. 1 (Ed. Narahashi, T), Published by Plenum Press, New York, pp.55-99)

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