Analysis of K+ and Na+ transport and intracellular contents during and after heat shock and their role in protein synthesis in rat hepatoma cells.

Heat shock at 42 degrees 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 degrees 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. Furthermore, 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 degrees (D. H. J. Schamhart et al., Radiat. 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+ contents 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 involvement of K+ and Na+ in the effects of heat shock on protein synthesis in Reuber H35 hepatoma cells.