Dendrotoxin‐sensitive K+ currents contribute to accommodation in murine spiral ganglion neurons

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Abstract
We have previously identified two broad electrophysiological classes of spiral ganglion neuron that differ in their rate of accommodation (Mo & Davis, 1997a). In order to understand the underlying ionic basis of these characteristic firing patterns, we used α‐dendrotoxin (α‐DTX) to eliminate the contribution of a class of voltage‐gated K+ channels and assessed its effects on a variety of electrophysiological properties by using the whole‐cell configuration of the patch‐clamp technique. Exposure to α‐DTX caused neurons that initially displayed rapid accommodation to fire continuously during 240 ms depolarizing test pulses within a restricted voltage range. We found a non‐monotonic relationship between number of action potentials fired and membrane potential in the presence of α‐DTX that peaked at voltages between –40 to –10 mV and declined at more depolarized and hyperpolarized test potentials. The α‐DTX‐sensitive current had two components that activated in different voltage ranges. Analysis of recordings made from acutely isolated neurons gave estimated half‐maximal activation voltages of –63 and 12 mV for the two components. Because α‐DTX blocks the Kv1.1, Kv1.2 and Kv1.6 subunits, we examined the action of the Kv1.1‐selective blocker dendrotoxin K (DTX‐K). We found that this antagonist reproduced the effects of α‐DTX on neuronal firing, and that the DTX‐K‐sensitive current also had two separate components. These data suggest that the transformation from a rapidly adapting to a slowly adapting firing pattern was mediated by the low voltage‐activated component of DTX‐sensitive current with a potential contribution from the high voltage‐activated component at more depolarized potentials. In addition, the effects of DTX‐K indicate that Kv1.1 subunits are important constituents of the underlying voltage‐gated potassium channels.

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