Alterations of calcium homeostasis in cultured rat astrocytes evoked by bioactive sphingolipids
Published online on May 13, 2014
Abstract
Aim
In the brain, alterations in sphingolipid metabolism contribute to several neurologic disorders; however, their effect on astrocytes is largely unknown. Here, we identified bioactive sphingolipids that affect intracellular free calcium concentration ([Ca2+]i), mobility of peptidergic secretory vesicles, signaling pathways involved in alterations of calcium homeostasis and explored the relationship between the stimulus‐evoked increase in [Ca2+]i and attenuation of vesicle mobility.
Methods
Confocal time‐lapse images were acquired to explore [Ca2+]i signals, the mobility of fluorescently tagged peptidergic vesicles and the structural integrity of the microtubules and actin filaments before and after the addition of exogenous sphingolipids to astrocytes.
Results
Fingolimod (FTY720), a recently introduced therapeutic for multiple sclerosis, and sphingosine, a releasable constituent of membrane sphingolipids, evoked long‐lasting increases in [Ca2+]i in the presence and absence of extracellular Ca2+; the evoked responses were diminished in the absence of extracellular Ca2+. Activation of phospholipase C and inositol‐1,4,5‐triphosphate receptors was necessary and sufficient to evoke increases in [Ca2+]i as revealed by the pharmacologic inhibitors; Ca2+ flux from the extracellular space intensified these responses several fold. The lipid‐evoked increases in [Ca2+]i coincided with the attenuated vesicle mobility. High and positive correlation between increase in [Ca2+]i and decrease in peptidergic vesicle mobility was confirmed independently in astrocytes exposed to evoked, transient Ca2+ signaling triggered by purinergic and glutamatergic stimulation.
Conclusion
Exogenously added cell‐permeable sphingosine‐like lipids exert complex, Ca2+‐dependent effects on astrocytes and likely alter their homeostatic function in vivo.
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