title: Heat shock increases cytosolic free Ca2+ concentration via Na(+)-Ca2+ exchange in human epidermoid A 431 cells.
abstract: This study characterized cytosolic free Ca2+ concentration ([Ca2+]i) in normal and thermally injured human epidermoid A 431 cells. The resting [Ca2+]i in normal cells at 37 degrees C was 87 +/- 5 nM (n = 105). When cells were subjected to hyperthermia (40-50 degrees C), [Ca2+]i increased in a temperature- and time-dependent manner. The maximal increase in cells exposed to 45 degrees C was observed at 20 min; [Ca2+]i returned to normal within 1 h. The heat-induced [Ca2+]i increase depended on the presence of external Ca2+. La3+ and Cd2+ but not Co2+, verapamil, or nifedipine attenuated the heat-induced [Ca2+]i increase. TMB-8 partially blocked the increase in [Ca2+]i but pertussis toxin and cholera toxin pretreatment did not. The magnitude of the heat-induced [Ca2+]i increase or 45Ca2+ uptake depended on the presence of extracellular Na+. Heat treatment reduced the apparent Michaelis constant for external Ca2+ from 490 +/- 91 to 210 +/- 60 microM, whereas the maximal velocity remained the same. The intracellular Na+ concentration decreased 62.5% after heating. The heat-induced [Ca2+]i increase was completely blocked by amiloride (5 microM) and 5'-(N,N-dimethyl)-amiloride (1 microM). These results suggest heat activates the Na(+)-Ca2+ exchange system so as to increase [Ca2+]i and reduce [Na+]i.
authors.affiliation: Department of Clinical Physiology, Walter Reed Army Institute of Research, Washington, DC 20307-5100.
authors.forename: J G
authors.initials: JG
authors.lastname: Kiang
authors.forename: M L
authors.initials: ML
authors.lastname: Koenig
authors.forename: R C
authors.initials: RC
authors.lastname: Smallridge
mesh_terms: D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D006358:Hot Temperature; D006801:Humans; D009994:Osmolar Concentration; D015290:Second Messenger Systems / Q000502:physiology; D012769:Shock / Q000209:etiology / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger; D014407:Tumor Cells, Cultured
chemical_list: D002121:Calcium Channel Blockers; D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D002118:Calcium