Effect of F-actin disruption on volume regulatory processes in trout hepatocytes

EBNER, H; SCHWARZBAUM, PJ; PAFUNDO DE; PELSTER, B; KRUMSCHNABEL, G

Edinburgh, Escocia.

Congreso; SEB annual main meeting; 2004

The importance of the F-actin network for volume regulatoryprocesses was investigated in trout hepatocytesby comparing cellular responses to anisotonic conditionsin the absence and presence of cytochalasin B (CB), aninhibitor of F-actin polymerisation. Following 40minutes of hypotonic exposure, regulatory volumedecrease amounted to 62% in control cells, but only 42%in CB-treated cells. During hypertonic conditions theregulatory volume increase of 70% observed in controlswas decreased to 46% in the presence of CB. Measurementsof intracellular pH (pHi) changes, indicatingactivity of acid- and base-transporters involved in volumeregulation, revealed significant acidification andalkalinization upon hypo-and hypertonic exposure, respectively.Incubation with CB, which by itself caused aslight decrease of pHi, did not affect pHichanges duringhypotonic conditions, but significantly diminished theincrease of pHi in hypertonic medium. Similarly, thedecrease of total cellular acid release observed duringhypotonic exposure in controls was not altered by preincubationwith CB, whereas the pronounced increasenoted in hypertonic medium was significantly reducedin CB-treated cells. Intracellular free Ca2q (Ca2q ) inicreased in hypo-and hypertonic medium in control cellsand under either condition the elevation of Ca2q wasisignificantly diminished in cells treated with CB. Altogether,our results suggest that the F-actin network playsa crucial role in the cellular responses to anisotonic conditions,possibly via interference with both the activityof ion transporters as well as with signalling cascadesresponsible for activation of volume regulatoryprocesses.