Parasitol Res (2006) 99: 317–320 DOI 10.1007/s00436-006-0192-1 REVIEW Thaïs Souto-Padrón . Ana Paula Lima . Rachel de Oliveira Ribeiro Effects of dibucaine on the endocytic/exocytic pathways in Trypanosoma cruzi Received: 28 February 2006 / Accepted: 9 March 2006 / Published online: 13 April 2006 # Springer-Verlag 2006 Abstract Although local anesthetics (LA) are considered primarily Na + -channel blockers in the past decade, an alternative action of LA as inhibitors of fusion among compartments of the endocytic/exocytic pathways was described. In epimastigote forms of Trypanosoma cruzi, we observed that 50 mM dibucaine reduced the rates of uptake of bovine serum albumin (BSA) and immunoglobulin to 60% of control values in addition to the delay of exocytosis of cysteine proteases. Fusion among endocytic compart- ments was not inhibited in the presence of dibucaine because previously labeled reservosomes was loaded with a second label in sequential pulse-chase experiments. However, dibucaine reduced the degradation of BSA–gold complex in the reservosomes, which was not caused either by an inhibition of the whole proteolytic activity of the parasite or by a reduction on the expression levels of cruzipain. The immunocytochemical analysis suggested that the inhibition of the degradation of gold-labeled BSA in reservosomes could be due to a subversion of the regular traffic of proteases toward the reservosomes in dibucaine- treated cells. Introduction In spite of the large amount of studies on local anesthetics, the mechanism of action of these substances is not well- understood. There are two hypotheses to explain the action of local anesthetics (LA). The first of them, the Lipid Hypothesis, considers that the LA effects are related to a nonspecific perturbation of the lipid bilayer structure. The second one, the Protein Hypothesis, is based on evidences of specific interactions of LA with distinct classes of proteins, such as cell membrane receptors, enzymes, and cytoskeleton proteins (Mayorga et al. 1993; Hollmann et al. 2001; Mondal and Chakrabarti 2002). Local anesthetics, such as quinacrine and dibucaine (Db), were found to inhibit the activation of a cytoplasmic, calcium-independent, phospholipase A 2 (iPLA 2 ), resulting to a significant inhibition of intracellular, membrane-bound compartments fusion along the endocytic and secretory pathways (Lennartz et al. 1997; De Figueiredo et al. 1998, 2000). Inhibition of such fusion results in a diminished capacity of the cells to internalize and/or secrete molecules such as transferrin, asialoglycoproteins, and lysozyme (Tolleshaugh et al. 1982; Hagiwara and Ozawa 1990; Balboa et al. 2003). The use of substances that interfere with homotypic and heterotypic fusions in the endocytic/ exocytic pathways can be used as a new approach to understand the nature of distinct compartments, mainly in cells where they have not been properly identified yet. The endocytic pathway of trypanosomatid parasites Trypanosomatids are flagellated protozoans, some of which are well-known pathogenic parasites of man, such as Trypanosoma brucei sp., Trypanosoma cruzi, and Leishmania spp. All of them are transmitted by insect vectors, and they interact with different cell types in their mammalian hosts, sometimes even invading these cells. The survival of such parasites in distinct environments requires exogenous growth factors that are internalized by fluid-phase and receptor-mediated endocytosis (Langreth and Balber 1975; De Souza et al. 1978; Coppens et al. 1987, 1992; Webster 1989; Soares and De Souza 1991; Sengupta et al. 1999). The endocytic pathway in trypanosomatids presents a singular architecture where the intracellular itinerary and delivery of internalized molecules vary significantly This review was presented at the International Symposium on Vesicle Trafficking in Parasitic Protozoa. T. Souto-Padrón (*) . R. de Oliveira Ribeiro Instituto de Microbiologia Prof. Paulo de Góes, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil e-mail: souto.padron@micro.ufrj.br A. P. Lima Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil