Influence of Cell Volume Changes on Autophagic Proteolysis in the Perfused Liver of Air-Breathing Walking Catfish (Clarias batrachus)

Exposure of perfused liver of walking catfish (Clarias batrachus) to hypotonicity (80 mOsmol/L)caused swelling of liver cells as evidenced by the increase in liver mass by 11.5%, and inhibition of [H-3]leucine release (as a measure of proteolysis) by 37% from the radiolabeled perfused liver. Whereas, exposure of perfused liver to hypertonicity (+80 mOsmol/L) caused shrinkage of liver cells as evidenced by the decrease in liver mass by 10.4%, and stimulation of [H-3] leucine release by 24%. Infusion of amino acids such as glutamine plus glycine (2mM each) also caused increase in liver cell volume as evidenced by the increase in liver mass by 8.9%, and inhibition of [H-3] leucine release by 29%. Adjustment of anisotonicity of the media without changing the NaCl concentration in the media had almost similar effects on proteolysis in the perfused liver. A direct correlation of cell volume changes or hydration status of liver cells with that of proteolysis was observed in the perfused liver regardless of whether the cell volume increase/decrease was evoked by anisotonic perfusion media or by the addition of amino acids. Thus, it appears that the increase/decrease in hepatic cell volume could be one of the important modulators for adjusting the autophagic proteolysis in walking catfish probably to avoid the adverse affects of osmotically induced cell volume changes, to preserve the hepatic cell function and for proper energy supply under osmotic stress. This is the first report of cell volume-sensitive changes of autophagic proteolysis in hepatic cells of any teleosts. J. Exp. Zool. 311A:115-124, 2009. (c) 2008 Wiley-Liss, Inc.