Survival of human epidermal keratinocytes after short-duration high temperature: synthesis of HSP70 and IL-8

Thermal injury by short pulses (1-30 s) of relatively high temperature (50-68 degrees C) was investigated in normal human epidermal keratinocytes (NHEK). NHEK were cultured on plastic cover-slips and dipped in medium held at various temperatures. Survival assessed by methylthiazol tetrazolium reduction assay at 6 days postheating demonstrated an inverse time-temperature relationship that indicated that most cells could survive after a 1-s, 60 degrees C exposure or a 30-s, 55 degrees C exposure. Arrhenius plots of the data indicated major transition points for cell injury at 50 and 60 degrees C. Heat shock protein 70 (HSP70) and interleukin-8 (IL-8) were both induced by elevation of temperature between 50 and 60 degrees C for as short a time as 1 s. HSP70 synthesis stimulated by short, high pulses of heat appeared to induce thermotolerance. These results demonstrate that brief exposure to relatively high temperature can induce HSP70 and IL-8 synthesis in keratinocytes.