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Polyunsaturated Fatty Acids Modifying Ion Channel Voltage Gating
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.ORCID iD: 0000-0001-8493-0114
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Voltage-gated ion channels play fundamental roles in neuronal excitability and therefore dysfunctional channels can cause disease. Epilepsy is such a disease, affecting about 1% of the population and being characterized by synchronous electric activity of large groups of neurons leading to various types of seizures. In this thesis, polyunsaturated fatty acids (PUFAs) were used as key substances to study a new pharmacological mechanism for how to induce opening of voltage-gated potassium (Kv) channels, and how this possibly can protect against epileptic activity. All experiments were performed on cloned Shaker Kv channels expressed in Xenopus laevis oocytes. Channel activity was recorded with the electrophysiological two-electrode voltage clamp technique.

First we showed that both PUFAs and cerebrospinal fluid from children on the ketogenic diet open the Shaker Kv channel by shifting the channel voltage dependence towards more negative voltages, as we would expect for an antiepileptic effect. By testing fatty acids and related compounds with different properties and under different conditions we identified the critical structural components needed for the beneficial effect: a flexible cis-polyunsaturated lipid tail in combination with a negatively charged carboxyl head group. If substituting the negative charge for a positive amine group, channel opening was instead impeded. By mutating and modifying the channel at strategic positions the PUFA-action site was localized to a lipid-exposed surface close to the channel’s voltage sensor. We also showed that PUFAs induce channel opening by electrostatically facilitating a final voltage-sensor movement. The PUFA efficiency is dependent on the channel’s profile of charged residues in the outer end of the voltage sensor. This implies channel-specific effects. Finally, computer simulations demonstrated that small changes in channel voltage dependence can have dramatic effects on cellular excitability.

Both the identified PUFA-action site and the mechanism by which PUFAs induce channel opening are novel and could potentially be very useful in future drug design of compounds targeting neuronal and cardiac excitability. Our work also suggests that PUFA-induced Kv channel opening could be one important component in the ketogenic diet used as alternative epilepsy treatment.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2011. , 51 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1235
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-68084ISBN: 978-91-7393-204-2OAI: oai:DiVA.org:liu-68084DiVA: diva2:416144
Public defence
2011-05-06, Linden, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 09:00 (English)
Opponent
Supervisors
Available from: 2011-05-10 Created: 2011-05-10 Last updated: 2013-09-03Bibliographically approved
List of papers
1. Polyunsaturated fatty acids and cerebrospinal fluid from children on the ketogenic diet open a voltage-gated K channel: A putative mechanism of antiseizure action
Open this publication in new window or tab >>Polyunsaturated fatty acids and cerebrospinal fluid from children on the ketogenic diet open a voltage-gated K channel: A putative mechanism of antiseizure action
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2008 (English)In: Epilepsy Research, ISSN 0920-1211, E-ISSN 1872-6844, Vol. 80, no 1, 57-66 p.Article in journal (Refereed) Published
Abstract [en]

Purpose: Many children with epilepsy do not satisfactorily respond to conventional pharmacological therapy, but to the ketogenic diet, a high-fat, low-carbohydrate diet. This diet increases the concentrations of ketone bodies and polyunsaturated fatty acids (PUFAs) in cerebrospinal fluid (CSF) and plasma. However, its anticonvulsant mechanism is not known. Methods: To investigate the mechanism by which the diet protects against seizures, we studied the effects of several PUFAs (docosahexaenoic acid, eicosapentaenoic acid, and linoleic acid), ketone bodies (β-hydroxybuturic acid and acetoacetic acid), and CSF from patients on the ketogenic diet on the voltage-gated Shaker K channel expressed in Xenopus oocytes. Results: We found that PUFAs at concentrations down to 21 μM clearly increased the K current by shifting the conductance versus voltage curve in negative direction along the voltage axis. CSF from patients on the ketogenic diet has similar but smaller effects. In contrast, high concentrations (1-5 mM) of ketone bodies did not affect the K current. Computer simulations showed that the observed shifts for clinically relevant concentrations of PUFAs, and CSF from patients could effectively impair repetitive firing. Conclusions: These data suggest that the ketogenic diet could prevent epileptic seizures by PUFA-induced openings of voltage-gated K channels. © 2008 Elsevier B.V. All rights reserved.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-43176 (URN)10.1016/j.eplepsyres.2008.03.013 (DOI)72319 (Local ID)72319 (Archive number)72319 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2013-09-03Bibliographically approved
2. Lipoelectric modification of ion channel voltage gating by polyunsaturated fatty acids
Open this publication in new window or tab >>Lipoelectric modification of ion channel voltage gating by polyunsaturated fatty acids
2008 (English)In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 95, no 5, 2242-2253 p.Article in journal (Refereed) Published
Abstract [en]

Polyunsaturated fatty acids (PUFAs) have beneficial effects on epileptic seizures and cardiac arrhythmia. We report that ω-3 and ω-6 all-cis-PUFAs affected the voltage dependence of the Shaker K channel by shifting the conductance versus voltage and the gating charge versus voltage curves in negative direction along the voltage axis. Uncharged methyl esters of the PUFAs did not affect the voltage dependence, whereas changes of pH and charge mutations on the channel surface affected the size of the shifts. This suggests an electrostatic effect on the channel's voltage sensors. Monounsaturated and saturated fatty acids, as well as trans-PUFAs did not affect the voltage dependence. This suggests that fatty acid tails with two or more cis double bonds are required to place the negative carboxylate charge of the PUFA in a position to affect the channel's voltage dependence. We propose that charged lipophilic compounds could play a role in regulating neuronal excitability by electrostatically affecting the channel's voltage sensor. We believe this provides a new approach for pharmacological treatment that is voltage sensor pharmacology. © 2008 by the Biophysical Society.

Keyword
Animals Docosahexaenoic Acids/metabolism Electrophysiology Fatty Acids, Unsaturated/analysis/*physiology Hydrogen-Ion Concentration Ion Channel Gating/*physiology Magnesium/physiology Membrane Potentials Oocytes/*physiology Patch-Clamp Techniques Shaker S
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-43208 (URN)10.1529/biophysj.108.130757 (DOI)72950 (Local ID)72950 (Archive number)72950 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2013-09-03Bibliographically approved
3. Electrostatic Tuning of Cellular Excitability
Open this publication in new window or tab >>Electrostatic Tuning of Cellular Excitability
2010 (English)In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 98, no 3, 396-403 p.Article in journal (Refereed) Published
Abstract [en]

Voltage-gated ion channels regulate the electric activity of excitable tissues, such as the heart and brain. Therefore, treatment for conditions of disturbed excitability is often based on drugs that target ion channels. In this study of a voltage-gated K channel, we propose what we believe to be a novel pharmacological mechanism for how to regulate channel activity. Charged lipophilic substances can tune channel opening, and consequently excitability, by an electrostatic interaction with the channels voltage sensors. The direction of the effect depends on the charge of the substance. This was shown by three compounds sharing an arachiclonyl backbone but bearing different charge: arachidonic acid, methyl arachidonate, and arachidonyl amine. Computer simulations of membrane excitability showed that small changes in the voltage dependence of Na and K channels have prominent impact on excitability and the tendency for repetitive firing. For instance, a shift in the voltage dependence of a K channel with -5 or +5 mV corresponds to a threefold increase or decrease in K channel density, respectively. We suggest that electrostatic tuning of ion channel activity constitutes a novel and powerful pharmacological approach with which to affect cellular excitability.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-54082 (URN)10.1016/j.bpj.2009.10.026 (DOI)000274313200006 ()
Note

Original Publication: Sara Börjesson, Teija Parkkari, Sven Hammarström and Fredrik Elinder, Electrostatic Tuning of Cellular Excitability, 2010, BIOPHYSICAL JOURNAL, (98), 3, 396-403. http://dx.doi.org/10.1016/j.bpj.2009.10.026 Copyright: Elsevier Science B.V., Amsterdam http://www.elsevier.com/

Available from: 2010-02-22 Created: 2010-02-22 Last updated: 2013-10-15Bibliographically approved
4. An electrostatic potassium channel opener targeting the final voltage-sensor transition
Open this publication in new window or tab >>An electrostatic potassium channel opener targeting the final voltage-sensor transition
2011 (English)In: The Journal of General Physiology, ISSN 0022-1295, Vol. 137, no 6, 563-577 p.Article in journal (Refereed) Published
Abstract [en]

Free polyunsaturated fatty acids (PUFAs) modulate the voltage dependence of voltage-gated ion channels. As an important consequence thereof, PUFAs can suppress epileptic seizures and cardiac arrhythmia. However, molecular details for the interaction between PUFA and ion channels are not well understood. In this study we have localized the site of action for PUFAs on the voltage-gated Shaker K channel, by introducing positive charges on the channel surface which potentiated the PUFA effect. We furthermore found that PUFA mainly affects the final voltage-sensor movement, which is closely linked to channel opening, and that specific charges at the extracellular end of the voltage sensor are critical for the PUFA effect. Because different voltage-gated K channels have different charge profiles, this implies channel-specific PUFA effects. The identified site and the pharmacological mechanism will potentially be very useful in future drug design of small-molecule compounds specifically targeting neuronal and cardiac excitability.

Place, publisher, year, edition, pages
The Rockefeller University Press, 2011
Keyword
Docosahexaenoic acid, ketogenic diet, voltage clamp, Xenopus oocytes
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-68083 (URN)10.1085/jgp.201110599 (DOI)000291047100008 ()
Note
Original Publication: Sara I Börjesson and Fredrik Elinder, An electrostatic potassium channel opener targeting the final voltage-sensor transition, 2011, The Journal of General Physiology, (137), 6, 563-577. http://dx.doi.org/10.1085/jgp.201110599 Licensee: The Rockefellow University Press http://www.rupress.org/ Available from: 2011-05-10 Created: 2011-05-10 Last updated: 2013-09-03Bibliographically approved

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