Do heavy ions cause microlesions in cell membranes?

Heavy ions are a hazard in manned deep space missions. It has been theoretically postulated that when they interact with cells, localized damage in the forms of "microlesions" may occur. Purported morphological evidence of these lesions, however, has not been confirmed in the most extensively studied tissue so far, the cornea. Recent morphological evidence from rat corneas demonstrated that holes in membranes do not form as consequence of heavy ion irradiation. This does not mean, however, that some other form of damage is excluded. For example such damage may be physiological in nature, impairing the ability of cells or tissues to function properly. In order to uncover any physiological effects, we investigated the microlesion question by monitoring the electrical potential difference across the endothelium of rat corneas in vitro before, during, and after irradiation. When the corneas were exposed to 1 Gy of 56Fe ions (450 and 600 MeV/a.m.u.), we detected no effect on this parameter. These results suggest that direct physical damage to cell membranes, as predicted by the microlesion theory, does not take place.