Protection against heat-induced cell killing by alanine

When L-alanine was added either to full growth medium or to Hanks' balanced salt solution (HBSS) prior to hyperthermia, survival of heated cells was significantly increased in a concentration-dependent manner. Maximal heat protection was not immediate, but required at least 1 h at 37 degrees C incubation prior to heating. Heat protection was principally reflected in an increased Dq on the 45 degrees C survival curve; for example, with 100 mM L-alanine, the Dq increased from approximately equal to 20 (control) to 30 min at 45 degrees C. Hyperthermia of 1 h at temperatures between 42 degrees C and 45 degrees C indicated that 100 mM alanine had shifted the isotoxic temperature by 0.5 degrees C. Comparable heat protection was also observed with D-alanine and amino acid dimers, such as alanyl-alanine or alanyl-leucine. Leucine at similar concentrations by itself, without alanine, did not protect cells against heat killing, but increased cellular heat sensitivity. The data suggest that heat protection by alanine does not require incorporation of alanine into cellular protein, but is mediated by the free amino acid.