Abstract
Oscillations of [Ca 2+] i which are believed to be important in regulation of cellular behaviour or gene expression, require Ca 2+ entry via capacitative Ca 2+ influx for store refilling. However, the mediator between Ca 2+ store content and activation of Ca 2+ influx is still elusive. There is also controversy about the role of the actin cytoskeleton in this coupling. Therefore, the importance of an intact actin cytoskeleton on ATP- and bradykinin-elicited Ca 2+ signalling was investigated in cultured rat astrocytes by treatment with cytochalasin D which changes the morphology of the cells from an extended to a rounded shape. Cytochalasin D-treated astrocytes were unable, upon prolonged stimulation with the P2Y receptor agonist ATP, to generate oscillations of [Ca 2+] i which are, however, seen in 54% of untreated control cells. In cytochalasin D-treated cells, the amplitude of the initial Ca 2+ response was reduced mainly by disturbing the Ca 2+ influx, and, moreover, the total Ca 2+ pool which is sensitive to thapsigargin or cyclopiazonic acid was diminished. Thus, disruption of the cytoskeleton blocks agonist-elicited [Ca 2+] i oscillations apparently by reducing the coupling efficiency between intracellular Ca 2+ stores and capacitative Ca 2+ entry.
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