The Na + /Ca 2+ exchanger, a counter-transport system working in concert with the plasma membrane Ca 2+ pump, Ca 2+ channels, and intracellular Ca 2+ store system plays a critical role in the control of intracellular calcium. In its forward mode (Ca 2+ efflux), the exchanger has an important physiological role for the rapid extrusion of large amounts of Ca Address correspondence and reprint requests to Reinaldo DiPolo, Laboratorio de Fisiología Celular, Instituto Venezolano de Investigaciones Científicas (IVIC), Apartado 21827, Caracas 1020A, Venezuela. E-mail: dipolor@ivic.ve Abbreviations used: 2-APB, 2-aminoethoxydiphenyl borate; CICR, calcium-induced calcium release; CMC, 4-chloro-m-cresol; ER, endoplasmic reticulum; GFAP, glial fibrillary acidic protein; RyRs, ryanodine receptors; SOCC, store operated Ca 2+ channels; Tg, thapsigargin.

. Here we show that at therapeutic concentrations, amiodarone has a profound effect on the viability of Leishmania mexicana promastigotes. Additionally, its effect on the viability of the parasite was greater against intracellular amastigotes than against promastigotes, and it did not affect the host cell. Using fluorimetric and confocal microscopy techniques, we also demonstrated that the mechanism of action of amiodarone was related to the disruption of intracellular Ca 2؉ homeostasis through a direct action not only on the mitochondria but also on the acidocalcisomes. On the other hand, analysis of the free sterols in promastigotes incubated with amiodarone showed that this drug also affected the biosynthesis of 5-dehydroepisterol, which results in squalene accumulation, thus suggesting that amiodarone inhibits the squalene epoxidase activity of the parasite. Taken together, the results obtained in the present work point to a more general effect of amiodarone in trypanosomatids, opening potential therapeutic possibilities for this infectious disease.

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The Na/Ca exchange is a highly regulated transport mechanism in which MgATP, a powerful modulatory intracellular substrate, has important implications for its function. As occurs with some preparations, in squid axons, nucleotide regulation is lost after membrane vesicle isolation. This has been a significant obstacle in the biochemical characterization of the MgATP effect. An important clue in solving this long-standing puzzle is presented in this work by showing that prolonged intracellular dialysis of squid axons produces a complete run down of the MgATP effect. Here we report that a soluble cytoplasmic factor isolated from fresh squid axoplasm and brain reconstitutes the MgATP stimulation of the Na-gradient-dependent 45Ca uptake in squid optic nerve membrane vesicles. Partial purification of this factor uncovers the presence of a novel 13 kDa soluble cytoplasmic protein (SCPr) which, when microinjected in ATP de-regulated dialyzed squid axons, completely restores the MgATP stimulation of Na(o)-dependent Ca efflux. We propose that in the squid preparation this SCPr constitutes the link between the nucleotide and target effector: the Na/Ca exchanger itself, or other plasma membrane structures which may secondarily interact with the exchanger.

Biopsies of 71 cases of atypical cutaneous leishmaniasis from Costa Rican patients were evaluated by histopathological procedures and attempts were made to culture Leishmania from nine biopsies. Leishmanin skin tests were carried out in 31 patients and 112 healthy individuals. Additional biopsies from 19 patients from Nicaragua were evaluated by routine histopathology. Ten biopsies were studied by confocal and nine by scanning electron microscopy. Inorganic material was analysed using an electron probe for microanalysis. Leishmania parasites were isolated from only two biopsies, but 90.3% of the patients from Costa Rica were leishmanin-positive, as were 27.7% of healthy individuals. Routine histopathological studies revealed naked granulomas formed by differentiated macrophages. Abundant inorganic material was observed in sections examined by confocal microscopy. Electron probe analysis revealed that silica and aluminium were the predominant elements in large particles. We postulate that the presence of this inorganic material, possibly of volcanic origin, in the skin may modulate the immunological response to Leishmania and may inhibit visceralization in the cases caused by Leishmania chagasi.