Iberiotoxin-sensitive large conductance Ca2+-dependent K+ (BK) channels regulate the spike configuration in the burst firing of cerebellar Purkinje neurons

Cerebellar Purkinje cells (PCs) are the sole output neurons of the cerebellar cortex. Mature PCs discharge either tonically Na+ spikes or bursts of Na+ spikes ending to a Ca2+ spike. These cells express inactivating and non-inactivating large conductance Ca2+-dependent K+ (BK) channels in their soma and dendrites. Somatic intracellular recording of acutely prepared brain slices was performed to examine the role of BK channels-mediated current in the tonic and burst firing of PCs. Continuous injection of a negative DC current was used to both suppress the spontaneous activity and stabilize the resting membrane potential around -70 mV. Then, the short depolarizing current injection was used to evoke spike discharge. For establishing of the burst firing, 4-aminopyridine (4-AP) was bath applied to the bath solution. Blockade of BK channels with iberiotoxin (IbTx); a specific blocker of BK channels, did not affect the Na+ spike configuration in the tonic firing but caused a remarkable change in the shape of Na+ and Ca2+ spikes in 4-AP-induced burst. Our results showed that during the burst firing, strong activation of IbTx-sensitive BK channels enhances the amplitude of fast afterhyperpolarization while decreases the duration of both Na+ and Ca2+ spikes. The current from these channels contributes to both the repolarizing of Na+ spike in the burst and setting of the amplitude of post-pulse AHP that occurs immediately after a depolarizing pulse. These data reveal an important role of IbTx-sensitive BK current in regulating of the spike configuration during the burst firing of PCs. (c) 2008 Elsevier B.V. All rights reserved.