A NONINVASIVE TECHNIQUE FOR CELL-VOLUME DETERMINATION IN PERFUSED-RAT-LIVER

1) In isolated perfused rat liver, the intracellular ([C-14]urea-accessible minus [H-3]inulin accessible) water space was determined from the washout profiles of simultaneously infused [H-3]inulin and [C-14]urea. The washout profile of infused [C-14]urea was indistinguishable from that of infused tritiated water. During normotonic perfusions and without hormones or amino acids in influent, the intracellular water space was 548 +/- 10-mu-l/g liver wet weight (n = 44). Use of [H-3]raffinose instead of [H-3]inulin as marker for the extracellular space yielded almost identical values for the intracellular water space (i.e. 98.9 +/- 0.2% of that found with [H-3]inulin/[C-14]urea). When volume-regulatory K+ fluxes were completed following hypo- and hypertonic exposure of perfused rat livers and a steady state was reached, the intracellular water space was found to be increased and decreased, respectively. The extent of anisotonic exposure was linearly related to the change of intracellular water space. 2) Anisotonicity-, glutamine- and glycine-induced liver mass changes were almost fully explained by the simultaneously occurring alterations of the intracellular water space, indicating that cell volume changes in perfused rat liver under these conditions are not accompanied by significant changes of the extracellular space. Volume-regulatory K+ (plus accompanying anion) efflux following hypotonic perfusion accounted for about 70-85% of regulatory cell volume decrease, which occurred during the first 10 min of hypotonic exposure. 3) Cell volume of isolated hepatocytes was determined as the "hepatocrit" after gentle contrifugation of the cell suspension. This approach yielded comparable values as observed in the intact perfused rat liver by measuring the intracellular water space during insulin-induced or hypotonic cell swelling, but yielded quantitatively different results during cell shrinkage following glucagon or hypertonic exposure. 4) The data show that liver cell volume in the intact organ can reliably and repeatedly be assessed by means of intracellular water space measurements with the [H-3]inulin/[C-14]urea washout technique. They further suggest that (i) mass changes of perfused liver are a suitable parameter to assess cell volume changes following glutamine, glycine or anisotonic exposure. (ii) In isolated perfused rat liver, anisotonic cell volume regulation is largely due to K+ (plus accompanying anion) movements, indicating that electroneutral osmolytes probably play a minor role in volume regulatory decrease.