Volume changes, metabolism and ion homeostasis during anisosmótic exposure of trout hepatocytes

10. PREM, C., GSTIR, R., MANZL, C., PAFUNDO, D., SCHWARZBAUM, P. J., PELSTER, B., Y KRUMSCHNABEL, G

Berlín, Alemania

Congreso; 96va reunión anual de la sociedad alemana de zoología; 2003

The impact anisosmotic exposure on cell volume, metabolism, and ion homeostasis was examinedin isolated trout hepatocytes. In hypo- and hyperosmotic medium hepatocytes respondedwith swelling and shrinkage, respectively, followed by regulatory volume changes towards theoriginal isosmotic cell volume. These volume changes were accompanied by significant alterationsof metabolic functions. In hyposmotic, but not in hyperosmotic medium, oxygen consumption(VO2) was significantly reduced, whereas both conditions caused a significant decrease ofglucose production. Lactate production was not affected by anisosmotic conditions.Intracellular free calcium concentration (Ca2+i) was also affected during anisosmotic exposure.At the cell population level hyposmotic conditions evoked a moderate and slowly developingincrease of Ca2+i, whereas hyperosmolarity caused a pronounced and sustained increase, whichpeaked at the time of maximum cell shrinkage, but clearly exceeded a mere concentration effectdue to volume reduction. Responses of individual cells were highly variable in hyposmoticmedium, with only 60% showing a clear increase of Ca2+i, while in hyperosmotic conditions allcells displayed elevated Ca2+i levels.Cell shrinkage was furthermore accompanied by a decrease of intracellular pH (pHi) which wasinsensitive to inhibitors of Na+/H+-exchange and Cl-/HCO3--exchange, but was prevented in Cl--free medium. In hyperosmotic medium pHi increased. This alkalinization was absent when Na+/H+-exchange was blocked, and it was significantly diminished upon inhibition of Cl-/HCO3--exchange. These findings suggesting an important role of these ion transporters in regulatoryvolume increase of trout hepatocytes.