Development of a hardened THz energy meter for use on the kilojoule-scale, short-pulse OMEGA EP laser.

A highly adaptable and robust terahertz (THz) energy meter is designed and implemented to detect energetic THz pulses from high-intensity (>1018 W/cm2) laser-plasma interactions on the OMEGA EP. THz radiation from the laser driven target is detected by a shielded pyrometer. A second identical pyrometer is used for background subtraction. The detector can be configured to detect THz pulses in the 1 mm to 30 µm (0.3- to 10-THz) range and pulse energies from joules to microjoules via changes in filtration, aperture size, and position. Additional polarization selective filtration can also be used to determine the THz pulse polarization. The design incorporates significant radiation and electromagnetic pulse shielding to survive and operate within the OMEGA EP radiation environment. We describe the design, operational principle, calibration, and testing of the THz energy meter. The pyrometers were calibrated using a benchtop laser and show linear sensitivity to up to 1000 nJ of absorbed energy. The initial results from four OMEGA EP THz experiments detected up to ∼15µJ at the detector, which can correspond to hundreds of mJ depending on THz emission and reflection models.

Effect of UV irradiation on cell surface protease activity and amino acid uptake.

The surface of most cells includes a coterie of resident proteins which act as receptors for a wide variety of ligands and other proteins which are potentially bioactive on cell-cell contact (juxtacrine effects), or else are released by enzyme activity to influence cell behaviour by autocrine or paracrine mechanisms. We previously found that UVC irradiation stimulates the release of TGFalpha from its membrane-bound preprocursor form whereby it acts as a stimulus to rapid, reparative cell multiplication; clearly this runs the risk hastening mitosis before UV-induced DNA damage is fully corrected, which in turn may increase the likelihood of residual lesions persisting and hence of new mutations being generated. We found that sublethal UVC irradiation (10 J m(-2)) of HeLa cell cultures also resulted in activation of ecto-aminopeptidase and ecto-endopeptidases which were maximal 16 and 20-24 h after irradiation, respectively. Both of these classes of protease were shown to be metalloproteases using a nonapeptide substrate (called P9) which is cognate to the N-terminal cleavage site of preproTGFalpha except for a reporter 125I-tyrosine [Piva et al., J. Cell. Biochem. 64 (1997) 353-368]. We now show that the N-terminal tyrosine cleaved from P9 by cell surface aminopeptidase activity, was found to be taken up by the cell resulting in its 10-25-fold concentration intracellularly, some two- to threefold higher than from a reservoir source, and may represent a novel salvage pathway for recovery of essential amino acids. Aminopeptidase activity was found to be both temperature- and FBS-dependent but was not reliant on ATP for its activity. Tyrosine transport across the cell membrane was also temperature and FBS-dependent but required ATP for maximal activity. UVC irradiation enhanced aminopeptidase activity but not tyrosine uptake by the cultures. The fraction of HeLa cells undergoing apoptosis increased in those cultures which were exposed to higher doses of UVC. The levels of ecto-aminopeptidase and ecto-endopeptidase activity in apoptotic cells were elevated compared to viable cells receiving the same dose of UVC. These results suggest that increased levels of cell surface protease activity in apoptotic cells would increase the amounts of free amino acids and growth factors in the extracellular medium and hence stimulate the proliferation of surrounding cells to replace those killed by UV irradiation.

Increased ecto-metallopeptidase activity in cells undergoing apoptosis.

Release from the cell surface of a variety of growth factors, cytokines, and proteases follows exposure to genetically stressful agents capable of inducing apoptosis and necrosis. Increased ectoprotease activity is responsible for their release. We show that increased activity of several metalloproteases on the HeLa cell surface occurs after stresses due to UVC, actinomycin D, cycloheximide, and cisplatinum, which induce the release of transforming growth factor-alpha (TGFalpha) and other bioactive molecules. The ectoprotease activities increase preferentially on apoptotic cells, while little change occurs in viable cells. Gross decreases, except for the putative TGFalphaase activity, accompany necrosis. These changes may contribute to tissue repair and the absence of an inflammatory reaction to apoptotic cell death. They appear to be due to preferential enzyme activation or to retention by cells undergoing significant categorical decreases in protein content.