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Calmodulin supports both inactivation and facilitation of L-type calcium channels

Nature volume 399, pages 159–162 (1999)Cite this article

Abstract

L-type Ca2+ channels support Ca2+ entry into cells, which triggers cardiac contraction1, controls hormone secretion from endocrine cells2 and initiates transcriptional events that support learning and memory3. These channels are examples of molecular signal-transduction units that regulate themselves through their own activity. Among the many types of voltage-gated Ca2+ channel, L-type Ca2+ channels particularly display inactivation and facilitation, both of which are closely linked to the earlier entry of Ca2+ ions4,5,6,7,8,9,10. Both forms of autoregulation have a significant impact on the amount of Ca2+ that enters the cell during repetitive activity, with major consequences downstream. Despite extensivebiophysical analysis9, the molecular basis of autoregulation remains unclear, although a putative Ca2+-binding EF-hand motif11,12 and a nearby consensus calmodulin-binding isoleucine-glutamine (‘IQ’) motif13,14 in the carboxy terminus of the α1C channel subunit have been implicated12,14,15,16. Here we show that calmodulin is a critical Ca2+ sensor for both inactivation and facilitation, and that the nature of the modulatory effect depends on residues within the IQ motif important for calmodulin binding. Replacement of the native isoleucine by alanine removed Ca2+-dependent inactivation and unmasked a strong facilitation; conversion of the same residue to glutamate eliminated both forms of autoregulation. These results indicate that the same calmodulin molecule may act as a Ca2+ sensor for both positive and negative modulation.

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Figure 1: Point mutations in the IQ motif of 77WT affect Ca2+-dependent inactivation.
Figure 2: Frequency-dependent facilitation of I Ca conducted by 77I/A.
Figure 3: Repriming experiments reveal Ca2+-dependent facilitation of 77WT and 77I/V.
Figure 4: A mutant calmodulin, CaM(3−), inhibits Ca2+-dependent inactivation and facilitation.
Figure 5: CaM interacts with the IQ motif of α1C.

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Acknowledgements

We thank J. Adelman and J. Maylie for providing CaM(WT) and CaM(−3), C. Klee and M. Ikura for helpful discussions, and H.van Hees for technical assistance. This work was supported by the Swiss National Science Foundation (H.R.), a Pfizer postdoctoral fellowship (G.S.P.), an MSTP training grant (K.D.), and grants from NIH (G.S.P.), NINDS, NIMH, the McKnight Foundation and the Mathers Charitable Trust (R.W.T.).

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Author notes

  1. Roger D. Zühlke, Geoffrey S. Pitt, Karl Deisseroth and Richard W. Tsien: These authors contributed equally to this work.

Authors and Affiliations

  1. Department of Pharmacology, University of Bern, 3010, Bern, Switzerland

    Roger D. Zühlke & Harald Reuter

  2. Division of Cardiovascular Medicine and Stanford University Medical School, Stanford, 94305-5426, California , USA

    Geoffrey S. Pitt

  3. Department of Molecular and Cellular Physiology, Stanford University Medical School, Stanford, 94305-5426, California, USA

    Geoffrey S. Pitt, Karl Deisseroth & Richard W. Tsien

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  1. Roger D. Zühlke
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Correspondence to Harald Reuter.

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Zühlke, R., Pitt, G., Deisseroth, K. et al. Calmodulin supports both inactivation and facilitation of L-type calcium channels. Nature 399, 159–162 (1999). https://doi.org/10.1038/20200

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