Voltage-dependent potassium currents during fast spikes of rat cerebellar Purkinje neurons: inhibition by BDS-I toxin.
We characterized the kinetics and pharmacological properties of voltage-activated potassium currents in rat cerebellar Purkinje neurons using recordings from nucleated patches, which allowed high resolution of activation and deactivation kinetics. Activation was exceptionally rapid, with 10-90% activation in about 400 mus at +30 mV, near the peak of the spike. Deactivation was also extremely rapid, with a decay time constant of about 300 mus near -80 mV. These rapid activation and deactivation kinetics are consistent with mediation by Kv3-family channels but are even faster than reported for Kv3-family channels in other neurons. The peptide toxin BDS-I had very little blocking effect on potassium currents elicited by 100-ms depolarizing steps, but the potassium current evoked by action potential waveforms was inhibited nearly completely. The mechanism of inhibition by BDS-I involves slowing of activation rather than total channel block, consistent with the effects described in cloned Kv3-family channels and this explains the dramatically different effects on currents evoked by short spikes versus voltage steps. As predicted from this mechanism, the effects of toxin on spike width were relatively modest (broadening by roughly 25%). These results show that BDS-I-sensitive channels with ultrafast activation and deactivation kinetics carry virtually all of the voltage-dependent potassium current underlying repolarization during normal Purkinje cell spikes.
Martina
Marco
M
Department of Physiology, Feinberg School of Medicine, Northwestern University, 303 East Chicago Avenue, Chicago, IL 60611, USA. m-martina@northwestern.edu
Metz
Alexia E
AE
Bean
Bruce P
BP
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002525:Cerebellar Cortex / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D003064:Cnidarian Venoms / Q000494:pharmacology*; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009924:Organ Culture Techniques; D024642:Potassium Channels, Voltage-Gated / Q000187:drug effects / Q000378:metabolism*; D011689:Purkinje Cells / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D051670:Shaw Potassium Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013997:Time Factors
C059796:BDS-I antiviral protein, Anemonia sulcata; D003064:Cnidarian Venoms; D024642:Potassium Channels, Voltage-Gated; D051670:Shaw Potassium Channels