We have previously demonstrated selection favoring the JG strain of Trypanosoma cruziin hearts of BALB/c mice that were chronically infected with an equal mixture of the monoclonal JG strain and a clone of the Colombian strain, Col1.7G2. To evaluate whether cell invasion efficiency drives this selection, we infected primary cultures of BALB/c cardiomyocytes using these same T. cruzi populations. Contrary to expectation, Col1.7G2 parasites invaded heart cell cultures in higher numbers than JG parasites; however, intracellular multiplication of JG parasites was more efficient than that of Col1.7G2 parasites. This phenomenon was only observed for cardiomyocytes and not for cultured Vero cells. Double infections (Col1.7G2 + JG) showed similar results. Even though invasion might influence tissue selection, our data strongly suggest that intracellular development is important to determine parasite tissue tropism.

A influência do teor e da composição química das ceras epicuticulares foliares de espécies da caatinga (Aspidosperma pyrifolium, Capparis yco, Maytenus rigida e Ziziphus joazeiro) e do cerrado (Aristolochia esperanzae, Didymopanax vinosum, Strychnos pseudoquina e Tocoyena formosa) foram avaliadas em relação à resistência à perda de água, através de um dispositivo experimental construído para essa finalidade. Em geral, as ceras das espécies da caatinga foram mais eficientes contra a perda de água que as das espécies do cerrado. O aumento da espessura dos depósitos cerosos de 40 até 90 mg.cm-2 não alterou significativamente a resistência à evaporação. A natureza química dos componentes das ceras revelou-se um fator importante na determinação do grau de resistência à evaporação. n-Alcanos e triterpenos alcoólicos foram os constituintes mais eficientes como barreiras à evaporação, enquanto hentriacontan-16-ona (uma cetona) e ácido ursólico (triterpeno com função carboxílica) foram menos eficazes. A maior eficiência das ceras epicuticulares de duas espécies da caatinga (C. yco e Z. joazeiro) provavelmente se deve à predominância de n-alcanos em sua composição. A menor eficiência das ceras epicuticulares de A. pyrifolium (outra espécie da caatinga), T. formosa e A. esperanzae (ambas espécies do cerrado), à predominância em suas ceras de ácido ursólico para as duas primeiras e hentriacontan-16-para a última.

The effects of the contents and chemical composition of the foliar epicuticular waxes of species from the caatinga (Aspidosperma pyrifolium, Capparis yco, Maytenus rigida and Ziziphus joazeiro) and cerrado (Aristolochia esperanzae, Didymopanax vinosum, Strychnos pseudoquina and Tocoyena formosa) were evaluated as to the resistance to water loss by means of an experimental device constructed for this purpose. In general, the waxes of the caatinga species investigated were more efficient against water loss than cerrado species. Increase of the thickness of the waxy deposits from 40 to 90m g.cm-2 had no significant effect on the resistance to water loss. The chemistry of the wax constituents was shown to be an important factor to determine the degree of resistance to evaporation. n-Alkanes and alcoholic triterpenes were the most efficient barriers, while hentriacontan-16-one (a ketone) and ursolic acid (an acid triterpene) revealed lowefficiency. The higher efficiency of the waxes of the leaves from caatinga species (mainly those of C. yco and Z. joazeiro) is probably accounted for the predominance of n-alkanes in their composition. The lower efficiency of the waxes of A. pyrifolium (caatinga), T. formosa and A. esperanzae (both species from the cerrado) is probably a consequence of the predominance of triterpenoids in the waxes of the two former species and hentriacontan-16-one in the latter.