Hyperthermal influence on intracellular free calcium concentration in cultured macrophages of mice

In this study, we have determined the fluorescence value of intracellular f ree calcium ([Ca2+](i)) in macrophages from mice cultured in different temp eratures (37 degrees C, 38 degrees C and 39 degrees C) by laser cytometer. The results indicate that hyperthermia caused elevations in the levels of [ Ca2+](i). The characteristic effects of hyperthermia were, 1) rapid changes in [Ca2+](i) concentration, that is to say, the fluorescence value of [Ca2 +](i) rose a few sec after hyperthermia; 2) a detectable relationship betwe en the fluorescence value and temperature during defined temperature (38 de grees C-39 degrees C) and time (0-3600 sec), 3) non-synchronous responses o f cells, in other words, the extent and time of elevation of [Ca2+](i) fluo rescence value were different among the cells of the same group. We thought [Ca2+](i) elevation induced by heat happened through the mechanism of IP3- induced calcium release (IICR) and calcium-induced calcium release (CICR). The heparin and procaine might lower the concentration of [Ca2+](i) during hyperthermia through the mechanism that IICR and CICR were inhibited respec tively. Free calcium influx from the extracellular medium was not thought t o be necessary for heat-induced [Ca2+](i) elevation.