Worm Breeder's Gazette 9(2): 105
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
We are continuing our investigations of cell survival/disfunction and mutagenesis as functions of accelerated ion irradiation. One assay for cell function is to irradiate L1's with a 4-cell gonad (the target) and to score the worms as adults for gonad morphology and output, i.e. brood size. The velocity and charge of the accelerated ions is varied to manipulate the structure of the track of energy deposited in the cells and the fluence is varied to control the number of tracks per cell from 1 to > 1000. A standard measure of energy deposition by ions is the Linear energy transfer (LET) which is the total energy deposited per unit track length usually in Kev/micron. A typical X-ray has a value of 1 in these units. In order to compare the effectiveness of different ions one normalizes to a reference standard - often Cobalt-60 gamma rays: to calculate the Relative Biological Effectiveness or RBE which is the ratio of absorbed dose of a test radiation to the dose of the reference standard required to produce the same biological effect. Shown below are 'inactivation curves' for some accelerated ions by using N2 larvae. Notice the strong dependence on LET at any given fluence. 50% and 37% normal brood size RBE versus LET curves have been constructed from this and other data and are shown below. The curves indicate that the most effective ions for gonad cell inactivation have LETs of about 200 KeV/micron (mammalian cells typically display maximum values of from 100 to 200). Above this LET energy is wasted (you can't kill a cell twice). Below 50 KeV/ m the particles may sometimes pass through cells without inactivating them as effectively as gamma rays supplying the same absorbed dose in a uniformly distributed fashion. Preliminary calculations of RBE vs LET using the eT1(III;V) mutagenesis assay reported previously (WBG 9(1):38) indicate a broad peak from LET = 25 to 200 KeV/micron and a high RBE value of 6 to 7. In examining DAPI stained animals irradiated as L1's we found that intestinal cells can be easily scored for inhibition of mitosis and formation of cytoplasmic bridges between daughter nuclei. The effect is does and LET dependent and follows about the same inactivation kinetics as brood size. We'll report more on this I-cell assay in the Nov. 1 issue. [See Figure 1] [See Figure 2]