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The Journal of Neuroscience, August 13, 2008, 28(33):8238-8245; doi:10.1523/JNEUROSCI.2274-08.2008

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Cellular/Molecular
Repolarizing Responses of BK_Ca–Cav Complexes Are Distinctly Shaped by Their Cav Subunits

Henrike Berkefeld and Bernd Fakler

Institute of Physiology, University of Freiburg, 79104 Freiburg, Germany

Correspondence should be addressed to Bernd Fakler, Institute of Physiology, University of Freiburg, Hermann-Herder-Strasse 7, 79104 Freiburg, Germany. Email: bernd.fakler{at}physiologie.uni-freiburg.de

Large-conductance Ca²⁺- and voltage-activated potassium (BK_Ca) channels shape the firing pattern in many types of excitable cell through their repolarizing K⁺ conductance. The onset and duration of the BK_Ca-mediated currents typically initiated by action potentials (APs) appear to be cell-type specific and were shown to vary between 1 ms and up to a few tens of milliseconds. In recent work, we showed that reliable activation of BK_Ca channels under cellular conditions is enabled by their integration into complexes with voltage-activated Ca²⁺ (Cav) channels that provide Ca²⁺ ions at concentrations sufficiently high (10 µM) for activation of BK_Ca in the physiological voltage range. Formation of BK_Ca–Cav complexes is restricted to a subset of Cav channels, Cav1.2 (L-type) and Cav2.1/2.2 (P/Q- and N-type), which differ greatly in their expression pattern and gating properties. Here, we reconstituted distinct BK_Ca–Cav complexes in Xenopus oocytes and culture cells and used patch-clamp recordings to compare the functional properties of BK_Ca–Cav1.2 and BK_Ca–Cav2.1 complexes. Under steady-state conditions, K⁺ currents mediated by BK_Ca–Cav2.1 complexes exhibit a considerably faster rise time and reach maximum at potentials markedly more negative than complexes formed by BK_Ca and Cav1.2, in line with the distinct steady-state activation and gating kinetics of the two Cav subtypes. When AP waveforms were used as a voltage command, K⁺ currents mediated by BK_Ca–Cav2.1 occurred at shorter APs and lasted longer than that of BK_Ca–Cav1.2. These results demonstrate that the repolarizing K⁺ currents through BK_Ca–Cav complexes are shaped by the respective Cav subunit and that the distinct Cav channels may adapt BK_Ca currents to the particular requirements of distinct types of cell.

Key words: Ca²⁺-activated K⁺ channels; Cav channels; BK_Ca channels; calcium signaling; action potential; potassium channel

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Received July 9, 2008; revised June 25, 2008; accepted July 1, 2008.

Correspondence should be addressed to Bernd Fakler, Institute of Physiology, University of Freiburg, Hermann-Herder-Strasse 7, 79104 Freiburg, Germany. Email: bernd.fakler{at}physiologie.uni-freiburg.de

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