CHANGES OF ACTIN CYTOSKELETON DURING SWELLING AND REGULATORY VOLUME DECREASE IN CULTURED ASTROCYTES

Swelling of cultured astrocytes exposed to hyposmotic medium modified the organization of the filamentous actin (F-actin) cytoskeleton, maki ng the actin network diffuse in the cell body but concentrated at foci corresponding to the tips of the cell projections retracted by swelli ng. This change was reversible, and, after 2 h, the actin cytoskeleton tended to recover, and cells regained their flat and stellate shape. Cytochalasins B and D (CB and CD, respectively), which disrupt the act in cytoskeleton, did not affect regulatory volume decrease (RVD) or th e swelling-activated efflux of Cl- and inositol, although 10 mu M CD i ncreased the basal efflux of taurine. The mercurial p-chloromercuriben zenesulfonate (0.5-1 mM), known to disrupt the membrane cytoskeleton i n isosmotic conditions, induced a 46, 50, and 38% release of [H-3]taur ine, I-125, and [H-3]inositol, respectively, causing cell shrinkage an d retraction of the cytoskeleton. Coincidently, the swelling-stimulate d release of [3H]taurine and I-125 was reduced by 60 and 30%, respecti vely. Results of this study do not exclude the possibility that change s in the actin cytoskeleton elicited by swelling are involved in mecha nisms of RVD and only indicate that the disruption caused by cytochala sins is unrelated to that process.