HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 586/2/427    most recent jphysiol.2007.145151v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Beck, A. Articles by Fleig, A. Search for Related Content PubMed PubMed Citation Articles by Beck, A. Articles by Fleig, A. Related Collections Cellular

¹ Queen's Center for Biomedical Research, Laboratory of Cell and Molecular Signalling, The Queen's Medical Center and John A. Burns School of Medicine, University of Hawaii, Honolulu, HI 96813, USA

Microglia are the main immunocompetent cells of the mammalian central nervous system (CNS). Activation of cultured microglial cells and subsequent release of nitric oxide and cytokines critically depends on intracellular calcium levels. Since microglia undergo dramatic morphological, biochemical and electrophysiological changes in response to pathological events in the CNS, we investigated temporal changes in expression levels of ion channels involved in cellular calcium homeostasis in mouse cortical microglial cells in culture. Specifically, we assessed the inward and delayed outward rectifier potassium currents (I_IRK and I_DRK), calcium (Ca²⁺) release-activated Ca²⁺ currents (I_CRAC) and Ca²⁺-activated TRPM4-like currents (I_CAN) in non-activated microglia and cells that were activated by exposure to lipopolysaccharide (LPS) between 3 and 48 h. Unstimulated microglial cells, subcultured from an astrocyte coculture, typically exhibited a ramified, rod-shaped morphology. During the first 3 days of culture cell size and shape were maintained, but the percentage of cells showing prominent I_IRK went up and those expressing I_DRK went down. Cells retaining I_DRK exhibited smaller amplitudes, whereas those of I_IRK and I_CRAC were not affected. However, after 24 h of exposure to 1 µg ml^–1 LPS, most cells showed an amoeboid (‘fried egg’-shaped) morphology with a 62% increase in cell capacitance. At that point in time, only 14% of the cells revealed I_IRK and 3% had I_DRK exclusively, whereas the majority of cells expressed both currents. The amplitudes of I_CRAC and I_IRK progressively decreased after stimulation, whereas I_DRK transiently reached a maximum after 6 h of LPS exposure and then returned to pre-stimulation expression levels. Cultured microglia also revealed TRPM4-like, Ca²⁺-activated non-selective currents (I_CAN) with an EC₅₀ of 1.2 µM [Ca²⁺]_i. The expression levels of this current did not change significantly during and after 24 h of LPS exposure. We propose that LPS-induced down-regulation of I_IRK and I_CRAC will reduce the cell's capacity to produce significant calcium influx upon receptor activation and result in decreased sensitivity to exogenous stimulation. In this scenario, I_CAN expression would remain constant, although its activity would automatically be reduced due to the diminished calcium influx capacity of the cell.

(Received 17 September 2007; accepted after revision 7 November 2007; first published online 8 November 2007)
Corresponding author A. Beck: Queen's Center for Biomedical Research, Laboratory of Cell and Molecular Signalling, The Queen's Medical Center and John A. Burns School of Medicine, University of Hawaii, Honolulu, HI 96813, USA. Email: abeck{at}queens.org