EFFECTS OF ANISOTONIC EXPOSURE ON DUCK HEPATITIS-B VIRUS-REPLICATION

In cultured hepatocytes from in vivo duck hepatitis B virus-infected d ucks the effect of medium osmolarity on viral replication was studied. A 10-day exposure to hypotonic media (277 mOsm/L due to removal of 26 mmol/L NaCl) lowered the duck hepatitis B virus DNA content of cells and of the medium by about 50%, whereas hyperosmotic exposure (421 mOs m/L by addition of 46 mmol/L NaCl) increased it about fourfold compare d with normotonic standard incubation medium (329 mOsm/L). The tissue levels of viral RNA transcripts increased during the 10 days of hypert onic exposure but decreased only slightly after hypoosmotic treatment. Western-blot analysis for the production of viral pre-S/S proteins re vealed a marked stimulation of viral protein synthesis in hypertonic m edia, whereas hypotonic exposure inhibited it. Conversely, total cellu lar protein synthesis as assessed from [H-3]leucine incorporation into acid-precipitable material decreased during hyperosmotic exposure but increased during hypoosmotic exposure. We noted a comparable increase of duck hepatitis B virus DNA when raffinose (80 mmol/L) was added to hypotonic or normotonic media, without change in the NaCl concentrati ons. This suggests that the effects of anisotonicity on viral replicat ion were not due to alterations of Na+ or Cl- activity in the incubati on media, but might reflect changes of cellular volume. The effects of anisotonicity on viral replication were only seen after exposure of m ore than 8 hr of the cells to anisotonicity. The findings suggest that the cellular volume is an important determinant for duck hepatitis B virus replication, yet the underlying molecular mechanisms remain elus ive.