Effect of hepatocyte swelling on microtubule stability and tubulin mRNA levels

Abstract

Incubation of isolated rat hepatocytes under conditions known to induce cell swelling caused several alterations in microtubule physiology. As shown by immunofluorescence microscopy experiments in the absence and presence of triethyllead or colchicine (two well-established microtubule inhibitors), an apparent stabilization of the microtubule network became evident in hepatocytes exposed to hypotonic (190 mosmol/L) conditions. A similar stabilizing effect was also observed upon cell swelling induced by addition of insulin (100 nmol/L) or glutamine (10 mmol/L). The differential microtubule stabilities were not attributed to a differential incorporation of the antimicrotubular agents into hepatocytes as shown by [3H]colchicine-uptake experiments. The swelling-induced alterations of microtubules may contribute to the swelling-induced changes of liver cell function: in perfused rat liver it was found that the established inhibitory effect of hypotonic cell swelling on hepatic proteolysis was largely abolished in presence of colchicine. Tubulin mRNA levels increased by 1.9-, 2.1- and 2.7-fold in isolated hepatocytes being exposed for 120 min to hypotonic medium, insulin, or glutamine, respectively. The results suggest an involvement of microtubular structures in the regulation of liver metabolism in response to alterations of the cellular hydration state.Key words: microtubules, cell swelling, glutamine, gene expression, proteolysis.