Synthesis in Rat Hepatoma Cells during and after Heat Shock and Their Role in Protein Transport and Intracellular Contents

Heat shock at 42°caused a rapid inhibition of protein synthesis in Reuber H35 hepatoma cells. Inhibition was maximal within 5 min after the temperature was increased. After heat shock at 42°for 30 min, protein synthesis was restored in 4 to 5 hr. Heat shock did not inhibit amino acid transport or cause a decrease of cellular amino acid pools, excluding a direct effect of these parameters on the inhibition of protein synthesis. The same heat shock caused a stimulation of Na+-K+ pump activity, as monitored by ouabain-sensitive Rb+ influx, but the activity returned rapidly to pretreated levels after heat shock. Similar effects were observed in the passive K+ efflux. Further more, heating did not affect the intracellular K+ and Na+ contents. A clear difference in the effect of temperature on protein synthesis and active K+ and Na+ influx was observed. In an Arrhenius plot, a sharp break for protein synthesis was observed at 40°(D. H. J. Schamhart et al., Radiât.Res., in press, 1984), while no discontinuity was observed in the Arrhenius plot for active K+ and Na+ influxes. The results demonstrate that, during and after heat shock and at various temperatures, the K+ and Na+ balances are in a continuous steady state. Experimental modification of the intracellular K+ and Na+ con tents by using ouabain or the Na* ionophore monensin revealed that, within large limits of intracellular cation contents, protein synthesis is unimpaired. These results exclude any direct involve ment of K+ and Na+ in the effects of heat shock on protein synthesis in Reuber H35 hepatoma cells.