The role of BK-type Ca super(2+)-dependent K super(+) channels in spike broadening during repetitive firing in rat hippocampal pyramidal cells

• Published in: The Journal of physiology Vol. 521; no. 1; pp. 135 - 146
• Main Authors: Shao, Li-Rong, Halvorsrud, Ragnhild, Borg-Graham, Lyle, Storm, Johan F
• Format: Journal Article
• Language: English
• Published: 01.11.1999
• Subjects: firing pattern
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1111/j.1469-7793.1999.00135.x

* 1 The role of large-conductance Ca super(2+)-dependent K super(+) channels (BK-channels; also known as maxi-K- or slo-channels) in spike broadening during repetitive firing was studied in CA1 pyramidal cells, using sharp electrode intracellular recordings in rat hippocampal slices, and computer modelling. * 2 Trains of action potentials elicited by depolarizing current pulses showed a progressive, frequency-dependent spike broadening, reflecting a reduced rate of repolarization. During a 50 ms long 5 spike train, the spike duration increased by 63.6 plus or minus 3.4% from the 1st to the 3rd spike. The amplitude of the fast after-hyperpolarization (fAHP) also rapidly declined during each train. * 3 Suppression of BK-channel activity with (a) the selective BK-channel blocker iberiotoxin (IbTX, 60 nM), (b) the non-peptidergic BK-channel blocker paxilline (2-10 mu M), or (c) calcium-free medium, broadened the 1st spike to a similar degree ( approximately 60%). BK-channel suppression also caused a similar change in spike waveform as observed during repetitive firing, and eliminated (occluded) most of the spike broadening during repetitive firing. * 4 Computer simulations using a reduced compartmental model with transient BK-channel current and 10 other active ionic currents, produced an activity-dependent spike broadening that was strongly reduced when the BK-channel inactivation mechanism was removed. * 5 These results, which are supported by recent voltage-clamp data, strongly suggest that in CA1 pyramidal cells, fast inactivation of a transient BK-channel current (I sub(CT)), substantially contributes to frequency-dependent spike broadening during repetitive firing.