We have previously shown that the binding of Trypanosoma cruzi trypomastigotes to glutaraldehyde-fixed mammalian cells has the characteristics of a receptor-mediated process and that it mimics the attachment step of the invasion of live cells by this parasite. In this study we examined the metabolic requirements for the attachment of trypomastigotes to glutaraldehyde-fixed fibroblasts. The attachment of trypomastigotes to fixed cells is prevented when the energy conservation mechanisms are inhibited with the drugs 2-deoxyglucose, sodium azide, antimycin, crystal violet, oligomycin, N,N'-dicyclohexylcarbodiimide, and carbonyl cyanide 3-chlorophenylhydrazone. However, under the same experimental conditions, the movement of parasites is not significantly affected. Several of these drugs totally inhibit the penetration of the parasite into live target cells. We conclude that the attachment of trypomastigotes to mammalian cells is an active process that requires trypomastigote energy. In addition, we present evidence that penetration into nonphagocytic cells can also be an active process. Trypomastigotes can be seen in scanning electron micrographs traversing extended lamellipodia and entering paraformaldehyde-fixed epithelial cells. Cytochalasin D, a drug that disrupts microfilaments and prevents the formation of plasma membrane extensions mediated by actin, had little or no effect on trypomastigote invasion, while it inhibited Salmonella entry into epithelial cells
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