Using permissive cell lines of epithelial or neuroglial origin, we found that scratch-wounding a small proportion of the recipient cells prior to prion exposure strongly reduced the cell culture's susceptibility to infection. We provide evidence suggesting that wound-triggered inhibition of prion infection was mediated by the release of nucleotides in the extracellular medium of injured cultures. While cell wounding or ATP treatment of unwounded target cells inhibited de novo infection, we found that they had no effect on steady-state infected cultures, indicating that these treatments affect the early stages of infection. These findings support the view that cells have the capacity to modulate their permissiveness to prion infection in response to external stimuli, such as a signalling molecule. (c) 2005 Elsevier Inc. All rights reserved.