Change search
ReferencesLink to record
Permanent link

Direct link
Extracellular Space dynamics contribute to Potassium kinetics during cortical spreading depression in Aquaporin-4 Deficient Mice
KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.ORCID iD: 0000-0003-0578-4003
Show others and affiliations
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Glial water channel aquaporin-4 (AQP4) plays an important role in neuroexcitation phenotypes that are highly associated with potassium homeostasis in brain extracellular space (ECS).  The mechanism of how AQP4 modulate the neuroexcitation through potassium redistribution during the neuronal signal transduction remains unknown.  Cortical spreading depression (CSD) is a self-propagating wave of neuronal depolarization with increased extracellular potassium concentration ([K+]o),  astrocyte swelling and subsequent severe contraction of ECS which provide a model for the mechanism study.  Here we characterized the CSD induced by KCl application in wild type (WT) and AQP4 deficient mice (AQP4-/-) and found AQP4-/- mice had a significant decrease in the frequency (6.9 ± 0.3 vs. 10.2 ± 0.5 CSDs/hr; p < 0.01), as well as the propagation velocity of CSD (2.9 ± 0.1 vs. 3.7 ± 0.1 mm/min; p < 0.05).  During CSD, the dynamic changes of extracellular potassium were determined using K+-selective microelectrodes and the extracellular space (ECS) was measured by TMA+ method.  We found the rate of K+ release and clearance was significantly prolonged in the AQP4-/- mice (t1/2, 10.2 ± 1.8 sec and 43.2 ± 2.3sec) compared to their WT counterparts (t1/2, 7.4 ± 0.3 sec and 35.7 ± 1.0 sec), which were paralleled by a significantly delayed contraction and recovery of ECS to baseline in AQP4-/- mice.  There is no difference in baseline or peak [K+]o. Importantly, no alterations were found in the expression or localization of inwardly rectifying K+ channel Kir4.1, gap junction hemichannel connexin-43, and anchor protein alpha-syntrophin in AQP4-/- mice.  A computer geometrical modeling of potassium accumulation and clearance during CSD confirmed the major role of ECS dynamic change in modulation of potassium kinetics. These results implicated an essential role of AQP4 in dynamic changes of ECS during CSD, which may be a new mechanism underlying the potassium kinetics and neuroexcitation.

URN: urn:nbn:se:kth:diva-11875OAI: diva2:287229
QC20100727Available from: 2010-01-18 Created: 2010-01-18 Last updated: 2010-07-27Bibliographically approved
In thesis
1. Modeling Biophysical Mechanisms underlying Cellular Homeostasis
Open this publication in new window or tab >>Modeling Biophysical Mechanisms underlying Cellular Homeostasis
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cellular homeostasis is the effort of all living cells to maintain their intracellular content when facing physiological change(s) in the extracellular environment. To date, cellular homeostasis is known to be regulated mainly by time-consuming active mechanisms and via multiple signaling pathways within the cells. The aim of this thesis is to show that time-efficient passive (physical) mechanisms also, under the control and regulation of bio-physical factors such as cell morphology and distribution and co-localization of transport proteins in the cell membrane, can regulate cellular homeostasis. This thesis has been developed in an interface between physics and biology and focuses on critical cases in which cells face physiologically unstable environments at their steady state and therefore may need a constituent effort to maintain their homeostasis. The main hypothesis here is that the cell geometry is oriented in such a way that cellular homeostasis is preserved in a given environment. For exploring these cases, comparative spatial models have been developed that combine transporting function of membrane proteins with simple versus complex geometries of cells. Models confirm the hypothesis and show that cell morphology, size of extracellular space and intercellular distances are important for a dynamic regulation of water and ion homeostasis at steady state. The main clue is the existence of diffusion limited space (DLS) in the bulk extracellular space (ECS). DLS can, despite being ECS, maintain its ionic content and water balance due a controlled function of transport proteins in the membrane facing part of DLS. This can significantly regulate cellular water and ion homeostasis and play an important role in cell physiology. In paper I, the role of DLS is explored in the kidney whereas paper II addresses the brain.

The response of cells to change in osmolarity is of critical importance for water homeostasis. Cells primarily respond to osmotic challenge by transport of water via their membranes. As water moves into or out of cells, the volumes of intra- and extracellular compartments consequently change. Water transport across the cell membrane is enhanced by a family of water channel proteins (aquaporins) which play important roles in regulation of both cell and the extracellular space dimensions. Paper III explores a role for aquaporins in renal K+ transport. Experimentally this role is suggested to be different from bulk water transport. In a geometrical model of a kidney principal cell with several DLS in the basolateral membrane, a biophysical role for DLS-aquaporins is suggested that also provides physiological relevance for this study. The biophysical function of water channels is then extensively explored in paper IV where the main focus has been the dynamics of the brain extracellular space following water transport. Both modeling and experimental data in this paper confirmed the importance of aquaporin-4 expressed in astrocytes for potassium kinetics in the brain extracellular space.

Finally, geometrically controlled transport mechanisms are studied on a molecular level, using silicon particles as a simplified model system for cell studies (paper V and VI). In paper V the role of electrostatic forces (around the nano-pores and in between the loaded material and the silicon surface) is studied with regard to transport processes.  In paper VI the roles of pore size and molecular weight of loaded material are studied. All together this thesis presents various modeling approaches that employ biophysical aspects of transport mechanisms combined with cell geometry to explain cell homeostasis and address cell physiology-based questions.   

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. xii, 60 p.
Trita-FYS, ISSN 0280-316X ; 2010:01
National Category
Condensed Matter Physics
urn:nbn:se:kth:diva-11880 (URN)978-91-7415-546-4 (ISBN)
Public defence
2010-02-04, FA32, AlbaNova University Center, Roslagstullsbacken 21, KTH, Stockholm, 13:00 (English)
QC20100727Available from: 2010-01-21 Created: 2010-01-18 Last updated: 2010-07-27Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Kamali-Zare, PadidehBrismar, Hjalmar
By organisation
Cell Physics

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 279 hits
ReferencesLink to record
Permanent link

Direct link