An investigation into the factors involved in hear death and thermal sensitivity in calliphora vicina R-D

Abstract

The phenomenon of death at high temperatures in the blowfly Calliphora vicina has been studied, with particular emphasis on the respiratory activity of isolated flight muscle mitochondria (sarcosomes). These sarcosomes showed differential sensitivity towards several factors when different substrates are being repired. In the presence of α-glycerophos-phate as substrate lower values for Q0(_2) , RCI and ADP : 0 are obtained when the sarcosomes were isolated using the proteolytic enzyme 'nagarse' as compared with values obtained when the sarcosomes were prepared in the absence of 'nagarse'. It was also found that isolated sarcosomes respiring different substrates require different reaction conditions in order to show maximal respiratory performance. Sarcosomes isolated from lethally heat treated flies showed impaired oxidative phosphorylation and loss of respiratory control when α-glycerophosphate is respired. However, in the presence of pyruvate and proline as substrates coupling is impaired but is still demonstrable. Experiments were carried out to determine the effect of heat treatments when the heat dose is split by an interval of recovery. It was found that the dose is accumulative unless the recovery period extends to 6 hours or more. Recovering of flies from a heat shock (L.D.(_0_), is temperature dependent withal high value for Q(_10). The effect of temperature on isolated sarcosomes indicated that the loss of respiratory control observed at the higher reaction temperatures might not be due to a general deterioration of the sarcosomal membranes, unless temperatures about 40ºC or higher are used. Sarcosomes are more sensitive to heat in vitro than in vivo. Sarcosomal α-glycerophosphate dehydrogenase has been studied following in vivo and in vitro heat treatment, and it was found to be relatively thermostable. Its specific activity and allosteric behaviour were not abolished by temperatures that are lethal to the whole animal. Ultrastructural studies show that isolated sarcosomes exhibited changes in their morphology in different respiratory states. Work with sarcosomes from heat dead flies support the biochemical data, showing a differential thermosensitivity of sarcosomal respiration with α-glycerophosphate as compared with pyruvate and proline respiration. Loss of the energized conformation seems to occur only in sarcosomes isolated from heat treated animals respiring on of-glycerophos-phate. No difference was seen in the appearance of the brain neurosecretory cells of control, lethally heated, or recovering flies. It is concluded that α-glycerophosphate dehydrogenase may not be the temperature –sensitive site, and that thermal injury is a membrane- phenomenon. The significance of the results is discussed, and suggestions are made for future work.