Hyperthermia induces transient changes in [Na+](i) and [K+](i) in mamm
alian cells. Since Cl- flux is coupled with Nat and K+ in several proc
esses, including cell volume control, we have measured the effects of
heat on [Cl-](i) using the chloride indicator, MQAE, with flow cytomet
ry. The mean basal level of [Cl-](i) in Chinese hamster ovary cells wa
s 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 w
hen measured immediately after heating. There was about a 3-fold decre
ase in [Na+](i) under the same conditions, as measured by Sodium Green
, The magnitude of the increase in [Cl-](i) depended upon time and tem
perature. The [Cl-](i) recovered in a time-dependent fashion to contro
l values by 30 min after heating. When cells were heated at 45.0 degre
es C for 30 min in the presence of 1.5 mM furosemide, the heat-induced
[Cl-](i) increase was completely blocked. Since furosemide inhibits t
he Na+/K+/2Cl(-) cotransporter, Cl- channels, and even Cl-HCO3 exchang
e, these ion transporters may be involved in the heat-induced increase
in [Cl-](i).