Disruption of actin cytoskeleton in cultured rat astrocytes suppresses ATP- and bradykinin-induced [Ca2+](i) oscillations by reducing the coupling efficiency between Ca2+ release, capacitative Ca2+ entry, and store refilling

Oscillations of [Ca2+](i) which are believed to be important in regulation of cellular behaviour or gene expression, require Ca2+ entry via capacitative Ca2+ influx for store refilling. However, the mediator between Ca2+ store content and activation of Ca2+ 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 Ca2+ 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 [Ca2+](i) which are, however, seen in 54% of untreated control cells. In cytochalasin D-treated cells, the amplitude of the initial Ca2+ response was reduced mainly by disturbing the Ca2+ influx, and, moreover, the total Ca2+ pool which is sensitive to thapsigargin or cyclopiazonic acid was diminished. Thus, disruption of the cytoskeleton blocks agonist-elicited [Ca2+](i) oscillations apparently by reducing the coupling efficiency between intracellular Ca2+ stores and capacitative Ca2+ entry. (C) 2000 IBRO. Published by Elsevier Science Ltd.