Effects of protein kinase C (PKC) inhibitors (H7, staurosporine, calphostin C) on thermotolerance development were investigated in temperature sensitive tsAF8 cells derived from Syrian hamster BHK21 cells. Cells were pre-heated at 45 degreesC for 20 min, incubated at 34 degreesC with PKC inhibitors for varying lengths of time, i.e. 1.25-10.0 h, and then heated at 45 degreesC for 30 min. Increasing survival fractions after the second heat treatment was inhibited by the treatment with H7 (40-160 muM), with staurosporine (0.05-1.0 muM), and with calphostin C (0.8, 1.2 muM) in a concentration dependent manner. When the concentrations of these PKC inhibitors were low, the restraint of increasing survival fractions was temporary, since survival fractions increased 3-7.5 h after pre-heating. However, the survival fractions were almost constant by the treatment with 160 muM H7 and 1.0 muM staurosporine. Induction of HSP72 after heat stress was investigated in tsAF8 and BHK21 cells. Cells were heated at 45 degreesC for 20 min and incubated at 34 or 39.7 degreesC (tsAF8), at 37 degreesC (BHK21). Intensity of intracellular fluorescence from HSP72 was measured by flow cytometry. HSP72 was induced in BHK21 cells, but there was no definite induction of HSP72 in tsAF8 cells at either 39.7 or 34 degreesC. These results suggest that PKC is related with the thermotolerance development in tsAF8 cells; however, HSP72 is not involved in the thermotolerance development in tsAF8 cells.