Importance of cytoskeletal elements in volume regulatory responses of trout hepatocytes

HANNES L. EBNER, ; ALEXANDRA CORDAS, ; DIEGO PAFUNDO; PABLO SCHWARZBAUM; BERND PELSTER; GERHARD KRUMSCHNABEL

AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY, INTEGRATIVE AND COMPARATIVE PHYSIOLOGY

AMER PHYSIOLOGICAL SOC

Año: 2005 vol. 289 p. 877 - 890

0363-6119

The role of cytoskeletal elements in volume regulation was studied introut hepatocytes by investigating changes in F-actin distributionduring anisotonic exposure and assessing the impact of cytoskeletondisruption on volume regulatory responses. Hypotonic challengecaused a significant decrease in the ratio of cortical to cytoplasmicF-actin, whereas this ratio was unaffected in hypertonic saline. Disruptionof microfilaments with cytochalasin B (CB) or cytochalasin Dsignificantly slowed volume recovery following hypo- and hypertonicexposure in both attached and suspended cells. The decrease of netproton release and the intracellular acidification elicited by hypotonicitywere unaltered by CB, whereas the increase of proton release inhypertonic saline was dramatically reduced. Because amiloride almostcompletely blocked the hypertonic increase of proton release andcytoskeleton disruption diminished the associated increase of intracellularpH (pHi), we suggest that F-actin disruption affected Na/Hexchanger activity. In line with this, pHi recovery after an ammoniumprepulse was significantly inhibited in CB-treated cells. The increaseof cytosolic Na under hypertonic conditions was not diminished but,rather, enhanced by F-actin disruption, presumably due to inhibitedNa-K-ATPase activity and stimulated Na channel activity. Theelevation of cytosolic Ca2 in hypertonic medium was significantlyreduced by CB. Altogether, our results indicate that the F-actinnetwork is of crucial importance in the cellular responses to anisotonicconditions, possibly via interaction with the activity of ion transportersand with signalling cascades responsible for their activation.Disruption of microtubules with colchicine had no effect on any of theparameters investigated.