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.