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Selective activation of Ca2+-activated K+ channels by co-localized Ca2+ channels in hippocampal neurons

Abstract

Calcium entry through voltage-gated calcium channels can activate either large- (BK) or small- (SK) conductance calcium-activated potassium channels. In hippocampal neurons, activation of BK channels underlies the falling phase of an action potential and generation of the fast afterhyperpolarization (AHP)1,2. In contrast, SK channel activation underlies generation of the slow AHP after a burst of action potentials3. The source of calcium for BK channel activation is unknown, but the slow AHP is blocked by dihydropyridine antagonists4,5, indicating that L-type calcium channels provide the calcium for activation of SK channels. It is not understood how this specialized coupling between calcium and potassium channels is achieved. Here we study channel activity in cell-attached patches from hippocampal neurons and report a unique specificity of coupling. L-type channels activate SK channels only, without activating BK channels present in the same patch. The delay between the opening of L-type channels and SK channels indicates that these channels are 50–150 nm apart. In contrast, N-type calcium channels activate BK channels only, with opening of the two channel types being nearlycoincident. This temporal association indicates that N and BK channels are very close. Finally, P/Q-type calcium channels do not couple to either SK or BK channels. These data indicate an absolute segregation of coupling between channels, and illustrate the functional importance of submembrane calcium microdomains.

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Figure 1: Selective activation of SK channels by co-localized L-type calcium channels in cell-attached patches.
Figure 2: SK and BK channels are activated in a patch after excision.
Figure 3: L-type and SK channels are separated by 50–150 nm.
Figure 4: N-type channels activate BK channels.
Figure 5: P/Q-type calcium channels do not activate calcium-activated potassium channels.

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Acknowledgements

We thank B. Hirschberg, J. Maylie, D. Shepherd and J. T. Williams for reading the manuscript, and D. Shepherd for cell preparation. This work was supported by the NIH (NINDS).

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Correspondence to Neil V. Marrion.

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Marrion, N., Tavalin, S. Selective activation of Ca2+-activated K+ channels by co-localized Ca2+ channels in hippocampal neurons. Nature 395, 900–905 (1998). https://doi.org/10.1038/27674

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