We transfected cultured hippocampal neurons with the cDNA of Kv1.3 to investigate how a specific ion channel influences excitability. In transfected neurons under voltage clamp we observed an additional outward current that was selectively blocked by margatoxin. Under current clamp the Kv1.3 neurons exhibited tonic firing over a wide range of stimulation. In untransfected neurons or in Kv1.3 cells blocked with margatoxin only a few action potentials were elicited before a stationary depolarized state was reached. We attribute the specific effect of Kv1.3 to its particularly slow deactivation near the resting potential. A computational model shows that in Kv1.3 neurons a continuous outward current arises during the interspike intervals. It expands the dynamic range of tonic firing to injection currents at which untransfected cells are driven into a stationary depolarized state.
Fig. 6: Recordings of a GFP-Kv1.3 neuron before and after addition of margatoxin (MgTx). (A) Voltage clamp before (dashed lines) and after (solid lines) bath application of 1 nM MgTx. Pulse protocol as in Figure 1A. (B) Recordings of the GFP-Kv1.3 neuron in response to 100 ms long current injections of 60, 140, 220, 300 and 380 pA. (C) Responses of the cell to the same stimuli after application of MgTx.
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