Inactivation of secretory phospholipase A2 by ionizing radiation.

The extracellular phospholipase A2s (PLA2) from cobra venom, rattlesnake venom, and porcine pancreas were analyzed by radiation inactivation to determine their functional aggregation states. The analysis was performed in the presence of the protein transferrin at two different concentrations of PLA2: 5 micrograms/ml. The small size of these proteins necessitated the use of high radiation dosages. The catalytic activity of all samples decreased as a single exponential as a function of radiation dosage, to > 97% inactivation. Target size analysis of these curves yielded sizes corresponding to dimers for all three PLA2s, indicating that all three enzymes exist as dimers or larger aggregates under the conditions studied. An analysis of the amount of intact protein remaining by sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed that the loss of protein also followed a dimeric size for all three PLA2s. The loss of protein as a dimer indicates that transfer of radiation energy is occurring between polypeptides.

Long-wave ultraviolet light induces phospholipase activation in cultured human epidermal keratinocytes.

Long wave ultraviolet radiation (UVA) has been shown to play an important role in the overall response of skin to solar radiation, including sunburn, tanning, premature aging, and non-melanoma skin cancer. UVA induction of inflammation in human skin is thought to be mediated by membrane lipid derived products. In order to investigate the mechanism of this response we examined the effect of UVA on phospholipid metabolism of human epidermal keratinocytes in culture. Keratinocytes were grown in serum free low calcium medium. The cells were prelabeled with [3H] arachidonic acid or [3H] choline and irradiated with UVA (Honle 2002-Hg vapor lamp). Identification and quantitation of specific membrane phospholipid-derived components was achieved using high-performance liquid chromatography, paper chromatography, and radioimmunoassay. UVA resulted in a linear dose dependent release of [3H] arachidonic acid into medium between 1 and 20 joule/cm2. This response was inhibited in an oxygen-reduced environment. The radiolabel released was predominantly free arachidonate and cyclooxygenase metabolites. Cyclooxygenase metabolites prostaglandin E2 and prostacyclin derivative, 6-keto-prostaglandin F1a, were stimulated following UVA irradiation, but the lipoxygenase metabolite, leukotriene B was not detected. Maximal release was measured immediately after irradiation and changed little over 24 h post-irradiation. UVA stimulated an increase of [3H] choline metabolites glycerophosphorylcholine and phosphorylcholine in media extracts suggesting UVA activation of phospholipase C and phospholipase A2 or diacylglyceride lipase.

[Postradiation changes of active ion transport systems of the CNS. The effect of superlethal doses of ionizing radiation on the Na,K pump in surviving brain slices]. / Postradiatsionnye izmeneniia v sistemakh aktivnogo transporta ionov v TsNS. Vliianie sverkletal'nykh doz ioniziruiushchei radiatsii na Na,K-nasos v perezhivaiushchikh srezakh mozga.

Active potassium ion transport in surviving sections of rat brain was irreversibly inhibited 6 min, 1 h and 6 h following whole-body single X irradiation. At the same time, the accumulation of products of lipid peroxidation and phospholipase hydrolysis was followed up during the development of radiation pathology. The relationship was noted between the postirradiation changes in the physicochemical status of lipids of the membrane and the impairment of its transport function.

[Endogenous phospholipase hydrolysis in radiation injury of animals]. / Endogennyi fosfolipaznyi gidroliz pri luchevom porazhenii zhivotnykh.

A study was made of the free fatty acid (FFA) content of homogenates of brain, thymus, liver, kidneys, erythrocytes, small intestine mucosa, and spleen of X-irradiated (7.76 Gy) rats. The increased FFA content was exhibited by all the organs under study. The increase was maximum in the thymus. Calcium ions were shown to play a defined role in the radiation enhancement of endogenous phospholipase hydrolysis.