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Received January 16, 2002
Accepted after revision May 7, 2002
1 Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, NJ 08854-8082, USA
2 Nelson Biological Laboratories, Rutgers University, 604 Allison Road, Piscataway, NJ 08854-8082, USA
* To whom correspondence should be addressed. E-mail: rldavis{at}rci.rutgers.edu.
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 
-dendrotoxin (-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 -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 -DTX that peaked at voltages between -40 to -10 mV and declined at more depolarized and hyperpolarized test potentials. The -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 -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 -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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