Thermal sensitivity and resistance of insulin-receptor binding

Membrane proteins may be key targets in thermal cell killing. In the present study, insulin binding to cellular receptors has been used as a probe for membrane protein behavior after heat shock (42-45 degrees C). Heating and binding studies were carried out on monolayers of HA-1 Chinese hamster ovary cells. Binding was unaffected by temperatures below 43 degrees C, but above this temperature (43-45 degrees C) it was inhibited in a time-temperature dependent manner. The kinetics of inhibition of insulin binding were similar to those for cell inactivation. Scatchard analysis indicated a decrease in receptor number rather than affinity for insulin in heated cells. In cells made resistant to further heat treatment (thermotolerant cells) by a mild pretreatment dose of hyperthermia (45 degrees C/10 min) insulin binding was also made heat resistant. Heating appeared to act directly on the insulin receptor rather than indirectly on subsequent energy dependent processes such as internalization. The data thus indicate that the fate of at least one membrane protein is closely tied up with the ultimate destiny of the cell per se after heating.