Ribosomal RNA sequences of Enterocytozoon bieneusi, Septata intestinalis and Ameson michaelis: phylogenetic construction and structural correspondence

The microsporidian species Enterocytozoon bieneusi, Septata intestinalis and Ameson michaelis were compared by using sequence data of their rRNA gene segments, which were amplified by polymerized chain reaction and directly sequenced. The forward primer 530f (5'-GTGCCATCCAGCCGCGG-3') was in the small subunit rRNA (SSU-rRNA) and the reverse primer 580r (5'-GGTCCGTGTTTCAAGACGG-3') was in the large subunit rRNA (LSU-rRNA). We have utilized these sequence data, the published data on Encephalitozoon cuniculi and Encephalitozoon hellem and our cloned SSU-rRNA genes from E. bieneusi and S. intestinalis to develop a phylogenetic tree for the microsporidia involved in human infection. The higher sequence similarities demonstrated between S. intestinalis and E. cuniculi support the placement of S. intestinalis in the family Encephalitozoonidae. This method of polymerized chain reaction rRNA phylogeny allows the establishment of phylogenetic relationships on limiting material where culture and electron microscopy are difficult or impossible and can be applied to archival material to expand the molecular phylogenetic analysis of the phylum Microspora. In addition, the highly variable region (E. coli numbering 590-650) and intergenic spacer regions in the microsporidia were noted to have structural correspondence, suggesting the possibility that they are coevolving.

Evidence for guanosine triphosphate--binding proteins in Trypanosoma cruzi

The transformation of the parasite Trypanosoma cruzi from the blood-borne trypomastigote to the intracellular amastigote constitutes a key clinical feature in the pathophysiology of Chagas' disease. That this transition occurs without change in the integrity of the plasma membrane of the parasite suggests the presence of biochemical structures, i.e., signal transduction systems, that convey information regarding the external milieu of the host so as to facilitate this transformation. In higher eukaryotes, it has been found that a heterotrimeric GTP-binding protein (G-protein), composed of alpha beta gamma subunits, constitutes a critical component of this complex. Two closely related groups of G-proteins are substrates for cholera toxin (CT)- (Gs) and pertussis toxin (PT)- (Gi1-3 and Go) dependent ADP ribosylation. In concert, they link plasma membrane receptors to adenylate cyclase, resulting in the stimulation or inhibition, respectively, of cAMP generation. In this report, we demonstrate the presence of both groups of G-proteins. Cholera toxin-dependent ADP ribosylation of 42- and 45-kD proteins was demonstrable in amastigotes (AMAST), in the cytosol of epimastigotes (EPI), and weakly in trypomastigotes (TRYP), suggesting the presence of the stimulatory GTP-binding protein, Gs, in T. cruzi. Antisera generated against the alpha s subunit of the Gs heterotrimeric protein (anti-alpha s) bound to a 45-kD protein CT substrate in the rank order TRYP >> AMAST approximately EPI cytosol. Immunoprecipitation of CT-32P-ADP-ribosylated membranes with anti-alpha s resulted in 42- and 45-kD proteins. However, no Gs-mediated activation of adenylate cyclase was demonstrable in reconstitution studies using cyc- lymphoma cells, which lack a functional Gs but possess a beta-adrenergic receptor and adenylyl cyclase enzyme. Pertussis toxin-catalyzed ADP ribosylation was demonstrable in 39-40-kD particulate proteins of EPI, less strongly in AMAST, and least in TRYP, consistent with the presence of inhibitory (Gi) and Go GTP-binding proteins. In support of this observation, immunochemical analysis of the PT substrates identified the presence of alpha o and alpha i1-2-3 in EPI, AMAST and TRYP, although, with the exception of alpha i3, both toxin and associated immunochemical PT substrates are decreased in AMAST and TRYP relative to EPI. Although the functions of these putative G-proteins in T. cruzi are still unclear, their expression may be regulated by the state of parasite differentiation.(ABSTRACT TRUNCATED AT 400 WORDS)

Diagnosis and treatment of common intestinal helminths. II: Common intestinal nematodes

In the second article of this series, we discuss the diagnosis and treatment of some important intestinal nematodes. Common parasites discussed in detail include Ascaris lumbricoides, Trichuris trichiura, hookworm, and Enterobius vermicularis (pinworm). In addition, Strongyloides stercoralis has emerged as an important pathogen in immunocompromised patients, and Capillaria philippinensis is now recognized as an important cause of diarrhea in Asia. Finally, anisakiasis and other illnesses due to parasitic nematodes are discussed.

Trypanosoma cruzi: effects of infection on receptor-mediated chronotropy and Ca2+ mobilization in rat cardiac myocytes

Acute Trypanosoma cruzi infection is commonly associated with disorders of impulse conduction and muscle contraction in heart. In order to determine the extent to which receptor function changed in response to infection, infected neonatal rat cardiac myocytes in culture were compared with matched controls with regard to chronotropic response and Ca2+ mobilization following the application of adrenergic agonists. At 7-9 days in culture (5-7 days postinfection), spontaneous beat rates of control myocytes were four times as rapid as those in infected cells. Control cells responded to 10(-5) M isoproterenol (ISO) and 10(-6) M norepinephrine (NE) with increases in beat rate of 34 and 40%, respectively. Effects of ISO on infected cells were similar, and adenylate cyclase activity was similar in control and infected cells when measured in the presence of ISO alone or in combination with Gpp(NH)p. NE produced a more marked chronotropic response in infected cultures and altered Ca2+ mobilization. NE treatment increased Ca2+ levels in control cardiac myocytes from 51.8 +/- 4.4 to 113 +/- 16 nM (in 0 Ca2+ medium) and from 85.2 +/- 6.8 to 131.3 +/- 24.5 nM (1 mM external Ca2+). In infected cardiac myocytes, NE increased Ca2+ from 116.8 +/- 17 to 164.7 +/- 9.6 nM (in 0 Ca2+ medium) and from 132.2 +/- 13.2 to 162.5 +/- 0.3 nM (1 mM Ca2+ medium). Thus, basal and alpha-adrenergic-stimulated Ca2+ levels were higher in infected than uninfected myocytes regardless of the extracellular Ca2+ levels, although the fractional increase in infected myocytes was significantly lower than that in controls (1.4- and 1.2-fold vs 2.2- and 1.5-fold). Therefore, both chronotropic and Ca(2+)-mobilization responses to the alpha-adrenergic agonist NE are altered in T. cruzi-infected cardiac myocytes; the chronotropic response of similarly infected cells to the beta-adrenergic agonist ISO was not affected. These data indicating that T. cruzi infection may be associated with a dissociation in responses to these agonists suggest a possible mechanism to explain, in part, the cardiac dysfunction characteristic of Chagas' disease.

Diagnosis and treatment of intestinal helminths. I. Common intestinal cestodes

Increase in travel and immigration has led to a heightened awareness of parasitic diseases among health professionals. Intestinal helminths are important human parasites. Cestodes or tapeworms comprise an important group of helminths. The diagnosis of tapeworm infections requires a skilled laboratory because serological tests are unavailable. In this first part of our review of intestinal helminths, we describe the salient features of the diagnosis and treatment of several important intestinal cestodes, including Diphyllobothrium latum, Taenia, Hymenolepis, and Dipylidium caninum. Niclosamide and praziquantel are the drugs of choice for tapeworm infections.

Small subunit rRNA sequence of Enterocytozoon bieneusi and its potential diagnostic role with use of the polymerase chain reaction

In the past several years, microsporidia have become recognized as another important group of opportunistic infections of immunocompromised patients, especially those with AIDS. Enteric infections with the noncultivatable microsporidian parasite Enterocytozoon bieneusi have been diagnosed from AIDS patients with chronic diarrhea, malabsorption, and wasting. The incidence of infection and mechanism of transmission of these organisms in humans is unknown. Several recent tests for human pathogens have been developed using rRNA genes as diagnostic probes. Using the polymerase chain reaction and conserved regions of the small subunit rRNA (SSU-rRNA) gene, the SSU-rRNA gene of E. bieneusi was successfully cloned and subsequently sequenced. Amplification of E. bieneusi rRNA could be demonstrated from intestinal biopsies from HIV-1-infected patients infected with E. bieneusi but not from intestinal biopsies from noninfected patients. This cloned SSU-rRNA gene was used to develop improved probes for detection of E. bieneusi in tissue of infected patients.

Evidence that myocardial pertussis toxin substrates are uniquely altered in acute murine Chagas' disease in a manner unrelated to myocardial dysfunction

In an effort to correlate biochemical characteristics of the beta-adrenergic receptor complex with myocardial function, mouse myocardial GTP-binding proteins, specifically substrates for pertussis toxin (PT), were analysed with regard to the influence of infection with Trypanosoma cruzi, the causative agent of Chagas' cardiomyopathy. Infection was found to decrease in a non-uniform manner the magnitude of ADP-ribosylation in the PT substrates. High detergent concentrations attenuated the infection-associated decrease in PT-dependent ADP-ribosylation. Infection also altered the kinetics of the PT-dependent ADP-ribosylation reaction from a time course wherein maximal PT-dependent ADP-ribosylation occurred after 12 h incubation in control animals to one in which maximal PT-dependent ADP-ribosylation occurred after 3 h incubation and thereafter declined. Immunochemical analysis of the PT-substrates revealed an infection-associated decrease in alpha i1, alpha o, an increase in alpha i2 and no change in alpha i3. Verapamil treatment, which prevents the clinical consequences of infection, did not influence any of the infection-associated changes in PT-dependent ADP-ribosylation of GTP-binding protein substrates or their immunochemical properties. Complementary studies using isolated rat neonatal cardiocytes infected with the parasite further substantiated the finding that the infection-associated decrease in PT-dependent ADP-ribosylation and the associated change in the kinetics of the reaction were properties uniquely associated with the presence of the parasite.

Efficacy of azithromycin for treating Babesia microti infection in the hamster model

Because of its prevalence and severity, Babesia microti infection is an important public health problem. The current treatment of choice is clindamycin plus quinine. However, in some cases other treatments are needed because of drug intolerance or relapse. The activity of azithromycin was investigated for treatment of babesiosis in the hamster model. All animals received vancomycin to prevent antibiotic-associated colitis. Quinine (250 mg/kg/day), azithromycin (150 mg/kg/day), and the combination of azithromycin and quinine were compared. A significant suppression of parasitemia was found in all treatment groups (combination had the greatest effect, followed by azithromycin, then quinine; P < .05). The mean survival was significantly prolonged in the combination group (P < .05). Azithromycin as monotherapy in a higher dose (300 mg/kg/day) also resulted in a significant prolongation of survival (P < .05). Spirogermanium and ciprofloxacin, which have been reported to have antimalarial activity, had no effect on parasitemia or survival in this experimental babesiosis model.

Parasitic infections in AIDS patients. Cryptosporidiosis, isosporiasis, microsporidiosis, cyclosporiasis

AIDS is characteristically associated with several intracellular enteric protozoan infections that often cause chronic and sometimes fatal intractable large-volume diarrhea. Until the AIDS epidemic, several of these parasitic infections were almost unknown as causes of human disease. This article reviews the diseases produced by cryptosporidia, isospora, cyclospora, and microsporidia in humans.

Taeniasis and cysticercosis

This article focuses on clinical issues of taeniasis and cysticercosis, including a comprehensive review of the clinical data, standard and latest chemotherapy, modern concepts of pathogenesis, conventional and advanced diagnostic tests, current epidemiology, and effective means of control. Fundamental parasitology is covered to familiarize physicians and scientists with the latest concepts of parasites.

Transepithelial Ca2+ and Mg2+ transport in the cortical thick ascending limb of Henle's loop of the mouse is a voltage-dependent process

The mechanisms responsible for transepithelial Ca2+ and Mg2+ in transport in the isolated perfused cortical thick ascending limb (cTAL) of Henle's loop of the mouse nephron were investigated by measuring transepithelial voltages (PDte) and transepithelial ion net fluxes (JNa, JCl, JK, JCa, JMg) by electron microprobe analysis. In the presence of furosemide (10(-4) mol.l-1, lumen) and diphenylamine-2-carboxylate (DPC, 10(-4) mol.l-1, bath), known inhibitors of NaCl reabsorption in the TAL, Ca2+ and Mg2+ reabsorption was completely inhibited. In the presence of furosemide, JCa fell from 0.75 +/- 0.07 to -0.08 +/- 0.09 pmol.min-1.mm-1 (n = 5), and JMg from 0.47 +/- 0.04 to -0.01 +/- 0.11 pmol.min-1.mm-1 (n = 5). In the presence of DPC, JCa fell from 0.57 +/- 0.08 to -0.07 +/- 0.11 pmol.min-1.mm-1 (n = 5), and JMg from 0.16 +/- 0.02 to -0.11 +/- 0.07 pmol.min-1.mm-1 (n = 5). With furosemide, inhibition of Ca2+ and Mg2+ transport was paralleled by a 93% inhibition of NaCl reabsorption, while in the presence of DPC there was a 60% reduction of NaCl reabsorption. These effects were fully reversed after removal of the inhibitors from the lumen or bath solutions. In the absence of active NaCl transport, a lumen-to-bath directed-NaCl gradient (lumen: 150 mM NaCl + furosemide, bath: 50 mM NaCl + 200 mM mannitol) generated a negative transepithelial dilution potential of -13.8 +/- 1.1 mV (n = 8) which induced a significant Ca2+ and Mg2+ secretion into the tubular lumen of -0.59 +/- 0.06 and -0.43 +/- 0.05 pmol.min-1.mm-1 (n = 8), respectively. A bath-to-lumen-directed NaCl gradient, on the other hand, (lumen: 50 mM NaCl + furosemide, bath: 150 mM NaCl) generated a positive transepithelial dilution potential of +15.9 +/- 0.6 mV (n = 7), inducing a significant Ca2+ and Mg2+ reabsorption of 0.62 +/- 0.08 and 0.38 +/- 0.07 pmol.min-1.mm-1 (n = 7), respectively. Linear regression analysis of individual Ca2+ and Mg2+ net flux data versus voltage indicated that JCa and JMg were highly correlated to PDte. In conclusion, these data indicate that transepithelial Ca2+ and Mg2+ reabsorption in the mouse cTAL is predominantly a passive process, driven by the lumen-positive PDte.

Hormonal stimulation of Ca2+ and Mg2+ transport in the cortical thick ascending limb of Henle's loop of the mouse: evidence for a change in the paracellular pathway permeability

Recent studies from our laboratory have shown that in the cortical thick ascending limb of Henle's loop of the mouse (cTAL) Ca2+ and Mg2+ are reabsorbed passively, via the paracellular shunt pathway. In the present study, cellular mechanisms responsible for the hormone-stimulated Ca2+ and Mg2+ transport were investigated. Transepithelial voltages (PDte) and transepithelial ion net fluxes (JNa, JCl, JK, JCa, JMg) were measured in isolated perfused mouse cTAL segments. Whether parathyroid hormone (PTH) is able to stimulate Ca2+ and Mg2+ reabsorption when active NaCl reabsorption and thus PDte, is abolished by luminal furosemide was first tested. With symmetrical lumen and bath Ringer's solutions, no Ca2+ and Mg2+ net transport was detectable, either in the absence or in the presence of PTH. In the presence of luminal furosemide and a chemically imposed lumen-to-bath directed NaCl gradient, which generates a lumen-negative PDte, PTH slightly but significantly increased Ca2+ and Mg2+ net secretion. In the presence of luminal furosemide and a chemically imposed bath-to-lumen-directed NaCl gradient, which generates a lumen-positive PDte, PTH slightly but significantly increased Ca2+ and Mg2+ net reabsorption. In view of the observed small effect of PTH on passive Ca2+ and Mg2+ movement, a possible interference of furosemide with the hormonal response was considered. To investigate this possibility, Ca2+ and Mg2+ transport was first stimulated with PTH in tubules under control conditions. Then active NaCl reabsorption was abolished by furosemide and the effect of PTH on JCa and JMg measured. In the absence of PDte and under symmetrical conditions, no Ca2+ and Mg2+ transport was detectable, either in the presence or absence of PTH. In the presence of a bath-to-lumen-directed NaCl gradient, Ca2+ and Mg2+ reabsorption was significantly higher in the presence than in the absence of PTH. Finally, when active NaCl transport was not inhibited by furosemide, but reduced by a bath-to-lumen-directed NaCl gradient, PTH strongly increased JCa and JMg, whereas only a small increase in PDte was noted. In conclusion, these data suggest that PTH exerts a dual action on Ca2+ and Mg2+ transport in the mouse cTAL by increasing the transepithelial driving force for Ca2+ and Mg2+ reabsorption through hormone-mediated PDte alterations and by modifying the passive permeability for Ca2+ and Mg2+ of the epithelium, very probably at the level of the paracellular shunt pathway.

Intestinal parasites in returned travelers

Travelers returning from third-world countries may become infected with a variety of intestinal parasites. Although protozoan infections are more frequently seen, intestinal worms are also encountered. If considered in the differential diagnosis, these infections usually are readily diagnosed and treated.

Imported malaria in the Bronx: review of 51 cases recorded from 1986 to 1991

The cases of 51 patients with malaria seen at the Albert Einstein College of Medicine hospitals from January 1986 to June 1991 are reviewed. Thirty-five patients acquired infection on journeys to their country of origin. Of these 35 patients, 83% of whom had lived in the United States for > or = 2 years, only 17% received antimalarial prophylaxis. Ten of the 51 patients were born and raised in the United States, and 70% received prophylaxis (P < .01). Six of the 51 patients were visitors to the United States from areas endemic for malaria. Overall, 64% of patients acquired malaria in West Africa, south of the Sahara; 20% in Asia; 8% in Ecuador; 6% in Haiti; and 4% in the Middle East. The majority of infections were due to Plasmodium falciparum. Six patients traveled to a zone endemic for malaria while pregnant, and none received prophylaxis. In nine of 13 patients who received prophylaxis, there was inadequate dosing or poor compliance. Individuals born in regions endemic for malaria are at high risk of acquiring malaria on return to their countries of origin and are less aware of the need for malaria prophylaxis than are other travelers.

Detection of HIV-1 protein and nucleic acid in enterochromaffin cells of HIV-1-seropositive patients

Diarrhea contributes significantly to the morbidity and mortality of patients with the acquired immunodeficiency syndrome (AIDS). Up to 50% of AIDS patients have diarrhea, and an etiologic agent for this cannot be identified in all of them. Recent evidence suggests that enterochromaffin cells may be infected by the human immunodeficiency virus type 1 (HIV-1) and may contribute to the unexplained diarrhea. To test this hypothesis further, endoscopic biopsies of duodena from 22 HIV-1 seropositive patients [17 with diarrhea (> 500 g/day and > 3 bowel movements/day), five without diarrhea] and from 15 normal controls (no HIV risk factors) without diarrhea were studied. Formalin-fixed and paraffin-embedded 5-microns sections were examined by immunocytochemistry, using a monoclonal antibody to the HIV-1 gp41 protein, and by in situ hybridization with a full-length biotinylated HIV-1 DNA probe. Positive staining for gp41 was detected in crypt cells, consistent with the location, size, and morphology of enterochromaffin cells, in 11 of 17 HIV-1-seropositive patients with diarrhea, and in none of five without diarrhea. Nucleic acid hybridization staining was performed in five of the 11 patients who had positive gp41 staining; all showed HIV nucleic acid sequences in similar cells. All three of the five patients with positive staining for HIV nucleic acid sequences had diarrhea for which no etiologic agent for diarrhea could be found, and one each had cryptosporidia or microsporidia. No staining was observed in any of the samples from normal control tissues. These results suggest that HIV-1 may infect enterochromaffin cells and possibly alter their function. This, in turn, may contribute to the diarrhea associated with AIDS.

Diagnosis of Encephalitozoon cuniculi infection by western blot and the use of cross-reactive antigens for the possible detection of microsporidiosis in humans

Microsporidia are very primitive, eukaryotic, obligate, intracellular, protozoan parasites. Encephalitozoon cuniculi, a microsporidian originally described from a rabbit infection, has been described in humans as well as in many species of laboratory animals. We report the detection of E. cuniculi by Western blotting in a rabbit with torticollis that was obtained from an Encephalitozoon-free colony. Cross-reactivity of this serum was observed with antigens prepared from several genera of microsporidia. Identical Western blotting patterns were obtained with sera obtained from a rabbit immunized with E. cuniculi that was purified from tissue culture cells. In addition, we were able to demonstrate cross-reactivity between E. cuniculi rabbit antisera and Enterocytozoon bieneusi antigens by indirect immunofluorescent assay techniques in human intestinal biopsy samples. These cross-reactions between microsporidia may be useful in developing diagnostic tests for non-cultivatable microsporidia such as Enterocytozoon bieneusi.

Chagas' disease

Chagas' disease, caused by Trypanosoma cruzi, is an important cause of morbidity in many countries in Latin America. The important modes of transmission are by the bite of the reduviid bug and blood transfusion. The organism exists in three morphological forms: trypomastigotes, amastigotes, and epimastigotes. The mechanism of transformation and differentiation is currently being explored, and signal transduction pathways of the parasites may be involved in this process. Parasite adherence to and invasion of host cells is a complex process involving complement, phospholipase, penetrin, neuraminidase, and hemolysin. Two clinical forms of the disease are recognized, acute and chronic. During the acute stage pathological damage is related to the presence of the parasite, whereas in the chronic stage few parasites are found. In recent years the roles of tumor necrosis factor, gamma interferon, and the interleukins in the pathogenesis of this infection have been reported. The common manifestations of chronic cardiomyopathy are arrhythmias and thromboembolic events. Autoimmune, neurogenic, and microvascular factors may be important in the pathogenesis of the cardiomyopathy. The gastrointestinal tract is another important target, and "mega syndromes" are common manifestations. The diagnosis and treatment of this infection are active areas of investigation. New serological and molecular biological techniques have improved the diagnosis of chronic infection. Exacerbations of T. cruzi infection have been reported for patients receiving immuno-suppressive therapy and for those with AIDS.

Cytokine gene expression of endothelial cells infected with Trypanosoma cruzi

Coronary microvascular spasm and platelet hyperreactivity have been implicated in the pathogenesis of Chagas' cardiomyopathy. To clarify further the role of the microvasculature in this disease, alterations in cytokine gene expression due to Trypanosoma cruzi infection of human umbilical vein endothelial cells were examined. Northern blot analysis of total RNA from endothelial cells demonstrated that interleukin (IL)-1 beta, IL-6, and colony-stimulating factor 1 (CSF-1) mRNA expression was absent or minimal in uninfected cells but significantly increased in infected cells. c-sis mRNA levels diminished with increased time of infection. In situ hybridization studies also demonstrated high levels of IL-6 mRNA in individual infected cells. Significant levels of IL-6 and IL-1 beta protein were detected in the supernatants of infected endothelial cells. The serum of an acutely infected individual contained high levels of IL-6 protein, suggesting the potential importance of cytokines secreted by the vascular endothelium in the pathogenesis of Chagas' cardiomyopathy.

Trypanosoma cruzi: mechanisms of intracellular calcium homeostasis

Regulation of intracellular Ca2+ homeostasis was characterized in epimastigote forms of Trypanosoma cruzi using the fluorescence probe Fura-2. Despite an increase in extracellular Ca2+, [Ca2+]o, from 0 to 2 mM, cytosolic Ca2+, [Ca2+]i, increased only from 85 +/- 9 to 185 +/- 21 nM, indicating the presence of highly efficient mechanisms for maintaining [Ca2+]i. Exposure to monovalent Na+ (monensin)-, K+ (valinomycin, nigericin)-, and divalent Ca2+ (ionomycin)-specific ionophores, uncouplers of mitochondrial respiration (oligomycin), inhibitors of Na+/K(+)-ATPase (ouabain), and Ca(2+)-sensitive ATPase (orthovanadate) in 0 or 1 mM [Ca2+]o resulted in perturbations of [Ca2+]i, the patterns of which suggested both sequestration and extrusion mechanisms. Following equilibration in 1 mM [Ca2+]o, incubation with orthovanadate markedly increased [Ca2+]i, results which are compatible with an active uptake of [Ca2+]i by endoplasmic reticulum. In contrast, equilibration in 0 or 1 mM [Ca2+]o did not influence the relatively smaller increase in [Ca2+]i following incubation with oligomycin, suggesting a minor role for the mitochondrial compartment. In cells previously equilibrated in 1 mM [Ca2+]o, exposure to monensin or ouabain, conditions known to decrease the [Na+]o/[Na+]i gradient, upon which the Na+/Ca2+ exchange pathways are dependent, markedly increased [Ca2+]i. In a complementary manner, decreasing the extracellular Na+ gradient with Li+ increased [Ca2+]i in a dose-dependent manner. Finally, the calcium channel blockers verapamil and isradipine inhibited the uptake of Ca2+ by greater than 50%, whereas diltiazem, nifedipine, and nicardipine were ineffective. The results suggest that epimastigote forms of T. cruzi maintain [Ca2+]i by uptake, sequestration, and extrusion mechanisms, with properties common to eukaryotic organisms.