POLYAMINE TRANSPORT-SYSTEMS IN ISOLATED RAT HEPATOCYTES DERIVED FROM RESTING AND REGENERATING LIVERS

Polyamines and their principal metabolite, gamma-aminobutyric acid (GABA), modulate eukaryotic cell growth. To determine whether the liver possesses specific polyamine transport sites and whether changes occur to these or GABA transport sites during hepatic regeneration, suspensions of rat hepatocytes derived from in situ collagenase perfusions of livers at times 0, 24, 18, and 72 h post-partial hepatectomy were incubated at 4, 20, and 37-degrees-C with various concentrations of the following ligands: [H-3]putrescine, [H-3]spermidine, [C-14]spermine, and [H-3] GABA together with or without excess unlabeled ligand, KCN, ouabain, or digitoxigenin. Of the ligands studied, only [C-14]spermine and [H-3]GABA were associated with specific binding to hepatocytes derived from nonregenerating livers. Spermine binding correlated with the concentration of hepatocytes in the incubation mixture and reached equilibrium within 60 min. The approximate affinity constant (K(D)) was 5.5 x 10(-5) Mol/10(6) hepatocytes, and maximum number of binding sites (B(max)) was 1.8 +/- 1.2 x 10(-7) mol.10(6) hepatocytes-1.min-1. Binding was neither temperature nor sodium dependent and was not inhibited by KCN, ouabain, digitoxigenin, other polyamines, or GABA. Aside from a 43% decrease in spermine binding at 24 h post-partial hepatectomy [5.1 +/- 1.1 vs. 8.9 +/- 3.1 x 10(3) disintegrations per minute (dpm)/10(6) hepatocytes at time 0, P < 0.05] and a 39% decrease in GABA binding (3.4 +/- 1.3 vs. 5.5 +/- 1.9 x 10(3) dpm/10(6) hepatocytes, P < 0.05), there were no significant changes in ligand binding during hepatic regeneration. These findings indicate that specific binding sites do not exist for putrescine or spermidine on adult rat hepatocytes derived from nonregenerating or regenerating livers following partial hepatectomy. On the other hand, specific binding sites do exist for spermine and GABA in both nonregenerating and regenerating livers but significantly decrease during early regeneration when maximal regenerative activity occurs.