Effects of hyperthermia on intracellular chloride

Hyperthermia induces transient changes in [Na+](i) and [K+](i) in mammalian cells. Since Cl- flux is coupled with Nat and K+ in several processes, including cell volume control, we have measured the effects of heat on [Cl-](i) using the chloride indicator, MQAE, with flow cytometry. The mean basal level of [Cl-](i) in Chinese hamster ovary cells was 12 mM. Cells heated at 42.0 degrees or 45.0 degrees C for 30 min had about a 2.5-fold increase in [Cl-](i) above unheated control values when measured immediately after heating. There was about a 3-fold decrease in [Na+](i) under the same conditions, as measured by Sodium Green, The magnitude of the increase in [Cl-](i) depended upon time and temperature. The [Cl-](i) recovered in a time-dependent fashion to control values by 30 min after heating. When cells were heated at 45.0 degrees C for 30 min in the presence of 1.5 mM furosemide, the heat-induced [Cl-](i) increase was completely blocked. Since furosemide inhibits the Na+/K+/2Cl(-) cotransporter, Cl- channels, and even Cl-HCO3 exchange, these ion transporters may be involved in the heat-induced increase in [Cl-](i).