Cardioprotective actions of verapamil on the beta-adrenergic receptor complex in acute canine Chagas' disease

The effect of verapamil treatment on the myocardial beta-adrenergic adenylyl cyclase complex in acute canine Chagas' disease was investigated. Relative to uninfected animals, 30 days of infection with T. cruzi reduced myocardial adenylyl cyclase activity by over 75%. With continuous verapamil treatment, the infection-associated reduction in adenylyl cyclase activity was less than 50%. The individual components of the beta-adrenergic receptor complex were characterized.

INFECTION

(1) increased right ventricular (RV) beta-adrenergic receptor (beta AR) density five-fold; (2) decreased left ventricle beta AR density by 20%; (3) reduced the proportion of high-affinity beta AR receptors to the same extent in both left and right ventricles; (4) reduced alpha s by 50% as determined by Western blot analysis, increased alpha 11-3 but did not change alpha 0; and (5) decreased the magnitude of pertussis-toxin-dependent [32P]ADP ribosylation by 60% as well as the proportion of [32P]ADP-ribose incorporated in alpha 0. Verapamil treatment of infected animals restored RV beta AR receptor density, alpha s and alpha i1-3 to control levels but had no influence on any aspect of pertussis-toxin-dependent [32P]ADP-ribosylation. Verapamil treatment of uninfected animals also: (1) increased beta-adrenergic adenylyl cyclase activity; (2) increased beta AR density in the RV but not the LV; (3) reduced high- to low-affinity beta-adrenergic receptors; and (4) affected only alpha i2 (50% decrease). The results indicate that the major actions of verapamil on the beta-adrenergic adenylyl cyclase complex in acute canine Chagas' disease may help to account for its cardioprotective effects.

A dynamic model for explaining changes in use of IADL/ADL care in the community

Evidence exists that support services for community elders vary with need. However, few controlled longitudinal analyses have been carried out regarding descriptive profiles of elders experiencing differential change in service levels -- the focus of analysis here. Using a multivariate profile procedure (PC-Group), 1,730 elders followed over an 18-month period were first classified according to change in functional status groupings that predicted change in hours of service over this period, and each group was subsequently subdivided. Five of nine profiles identified (82% of the sample) were relatively stable functionally. In general, changes in service levels reflected change in functional status; profiles reflected differential change in service level depending upon whether functional status declined; the network provided an unusually high level of service (overextended) at baseline; or the informal network consisted exclusively of children.

Compromised microcirculation in acute murine Trypanosoma cruzi infection

Microvascular compromise has been 1 of many factors implicated in the etiology of the cardiomyopathy associated with Chagas' disease. To further assess the effect of Trypanosoma cruzi infection on the microcirculation, we examined the cremaster microvascular model in CD-1 male mice infected with the Brazil strain at 20-25 days postinfection. There was a significant decrease in red cell velocity (Vrbc) in first and third-order arterioles and venules, which was reversed by verapamil treatment. Video recordings revealed a marked inflammatory response that was confirmed by transmission electron microscopy. A marked inflammatory response was not seen in verapamil-treated infected mice. Segmental vasospasm and dilatation was evident in the microvascular bed of infected mice. This was not seen in control or verapamil-treated mice. This model provides a readily accessible method to observe directly the effects of T. cruzi infection on the microcirculatory flow in vivo. In addition, it confirms and extends our previous observations regarding T. cruzi-associated microvascular spasm and underscores a role for verapamil, a calcium-channel blocker, in the amelioration of the Chagas' disease.

Release of guanosine triphosphate binding protein alpha subunits from mouse myocardial membranes: basic properties and their alterations in acute murine Chagas disease

OBJECTIVE

The aim was to investigate the arrangement of heterotrimeric alpha beta gamma G proteins in myocardial membranes using GTP gamma S dependent release characteristics of their alpha subunits in acute murine Chagas disease.

METHODS

The properties of GTP gamma S dependent alpha subunit release were monitored immunochemically as well as by cholera toxin and pertussis toxin catalysed [32P]ADP ribosylation.

RESULTS

GTP gamma S, as opposed to other nucleotides, caused optimal and virtually instantaneous release of soluble 40 kDa [32P]ADP ribosylated protein in pertussis toxin treated membranes. When determined immunochemically, infection decreased both the sensitivity to GTP gamma S dependent release of alpha i subunits and appeared to facilitate the appearance of GTP gamma S dependent release of alpha i3. GTP gamma S also caused the release of soluble 45 and 40 kDa proteins as detected by cholera toxin-[32P]ADP ribosylated membranes and immunochemical analysis. With regard to cholera toxin-[32P]ADP ribosylated Gs substrates sensitive to GTP gamma S dependent release, infection (1) decreased the amount of 45 kDa alpha s protein, (2) increased the amount of 40 kDa protein, and (3) enhanced sensitivity to GTP gamma S. In contrast, there was no effect of infection on the magnitude or sensitivity to GTP gamma S dependent release of immunochemical alpha s.

CONCLUSIONS

The diverse characteristics of GTP gamma S dependent release of the very similar alpha subunits from myocardial membranes and their unique sensitivity to infection with T cruzi suggest that these very similar proteins are arranged within the plasma membrane in such a manner as to modify their biochemical behaviour.

Primary structure of the neuronal clathrin-associated protein auxilin and its expression in bacteria

The protein auxilin is a coat component of brain clathrin-coated vesicles. It interacts directly with the heavy chain of clathrin and supports its assembly into regular cages [Ahle, S. & Ungewickell, E. (1990) J. Cell Biol. 111, 19-29]. The combined open reading frames of three cow brain cDNA clones with a total of 4531 nucleotides predict a molecular mass of 99,504 Da for auxilin. The coding region is followed by a very long untranslated region of at least 1670 nucleotides. By Northern analysis, auxilin transcripts are found only in brain tissue. Auxilin is not related to any of the previously sequenced clathrin-binding proteins, but the region of positions 50-350 is 29% identical (similarity 56%) to the corresponding region of the actin-binding protein tensin from chicken fibroblasts. Recombinant auxilin expressed in and purified from bacteria by affinity chromatography is functional with respect to clathrin binding.

Synaptic vesicle recycling. The Ferrari of endocytosis?

After neurotransmission, neurons internalize and recycle the membrane components of synaptic vesicles remarkably quickly; they may have a 'rebuilt, turbo-charged' endocytic engine to achieve these speeds.

Trypanosoma cruzi induces endothelin release from endothelial cells

The potential role of endothelin-1 (ET-1) in the pathogenesis of focal microvascular spasm, previously implicated in the etiology of Chagas' cardiomyopathy, was investigated. There was an increase in ET-1 in the supernatants of Trypanosoma cruzi--infected human umbilical vein endothelial cells (HUVEC). Infection of HUVEC and vascular smooth muscle cells had no effect on the synthesis of transforming growth factor-beta, which induces ET-1 synthesis. Bioassay studies of isolated rat aortic rings revealed that the increases in ET-1 production were associated with augmented contractile responses, which were significantly attenuated by preincubation with the ETA receptor antagonist, BQ-123. When big ET was incubated with the parasite, there was no conversion of the precursor to the active hormone (ET-1), demonstrating that the parasite did not possess the necessary converting enzyme. These observations suggest the potential importance of ET-1 in the etiology of the microvascular spasm associated with Chagas' disease.

Pneumocandin D0, a new antifungal agent and potent inhibitor of Pneumocystis carinii

Pneumocandin D0 (9), a new member of the echinocandin class of antifungal agents, has been isolated as a minor constituent from fermentation broths of the filamentous fungi Zalerion arboricola (ATCC 20957). The structure of 9 has been determined mainly on the basis of spectroscopic analysis and by comparison with published data for similar compounds. To date, pneumocandin D0 has been found to be the most potent inhibitor of Pneumocystis carinii development in vivo within the natural-occurring echinocandin family of antifungal agents.

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)

Neonatal renal candidiasis

A case is presented of renal candidiasis complicated by obstructive uropathy in a 4 month old infant. Management was successful with surgical decompression combined with peri-operative amphotericin B, followed by 3 weeks of oral ketoconazole and subsequently 6 weeks of oral fluconazole. Fluconazole was substituted for ketoconazole owing to persistent candiduria, and achieved rapid urinary sterilization. Fluconazole is an effective and less toxic alternative to prolonged courses of amphotericin B in the treatment of neonatal renal candidiasis.

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.

Effects of changing contingencies on the behavior of depressed and nondepressed individuals

The effects of rules versus shaping on the behavior of depressed and nondepressed individuals were compared. Extending the findings in the depressive realism literature to a learning paradigm, the behavior of depressed individuals was more sensitive to changing contingencies than was the behavior of nondepressed individuals. Contrary to hypotheses, however, this effect appeared due primarily to the nondepressive Ss' strategy of continuing to follow an experimenter's inaccurate rules. Results suggest the relative absence of self-presentational concerns may lead depressed individuals to be more accurate in judging environmental contingencies.

Adaptations of myocardial beta-adrenergic receptor complex in hibernating marmots

Properties of marmot (Marmota flaviventris) myocardial beta-adrenergic receptor complex (beta-AR) were evaluated during hibernation (H), in summer (S) animals, and in animals aroused from hibernation (C). The results obtained for S and C animals were identical, and only the results for C animals are shown. In H-animal myocardial membrane preparations assayed at 37 degrees C, isoproterenol-dependent adenylate cyclase activity (ACA) was consistently higher, whereas the synergistic contribution of 5'-guanylylimidodiphosphate [Gpp(NH)p] in this reaction was reduced. When assayed at 10 degrees C, only the ACA in H animals responded to the combination of isoproterenol and Gpp(NH)p. In contrast, at 10 degrees C, ACA in response to Gpp(NH)p alone is essentially equal in H and C animals. Hibernation did not change myocardial beta-AR receptor density or affinity. In contrast, analysis of isoproterenol displacement of [125I]iodocyanopindolol revealed that the proportion of beta-AR in the high-affinity state was substantially greater in H than in C animals, and this relationship was retained even in the presence of Gpp-(NH)p. In an evaluation of the role of the GTP binding proteins that couple the beta-AR to the effector adenyl cyclase, we determined that there was no change in the cholera toxin- or pertussis toxin-dependent ADP ribosylation patterns. Immunochemical detection of the individual GTP binding proteins revealed no change in the levels of G alpha i1, G alpha i2, or G alpha i3. In contrast, we observed a hibernation-associated decrease in G alpha o associated with the plasma membrane-enriched particulate fraction. (ABSTRACT TRUNCATED AT 250 WORDS)

Estrogen uncouples beta-adrenergic receptor from the stimulatory guanine nucleotide-binding protein in female rat hypothalamus

The responsiveness of adenylyl cyclase to beta-adrenergic receptor stimulation was investigated in membranes prepared from hypothalamus-preoptic area and cortex of ovariectomized female rats injected with oil vehicle or estradiol benzoate 24 or 48 h before death. Membranes from the hypothalamus-preoptic area of ovariectomized animals displayed a concentration-dependent stimulation of adenylyl cyclase when incubated with the beta-adrenergic receptor agonist, isoproterenol (10(-7)-10(-5) M). This response was suppressed in membranes from estrogen-treated animals. The effect of estrogen was observed 48 h, but not 24 h, after hormone administration. In addition, estrogen had no measurable effect on hypothalamic adenylyl cyclase activation by either GTP (10(-8)-10(-5) M) or forskolin (10(-8)-10(-6) M), on beta-adrenergic receptor density, or on antagonist binding affinity measured with the beta-adrenergic antagonist [125I]iodocyanopindolol. Analysis of isoproterenol displacement of iodocyanopindolol binding revealed that estrogen reduced agonist binding affinity in hypothalamus-preoptic area membranes. In membranes from ovariectomized controls, high affinity agonist binding to the beta-adrenergic receptor was apparent and was abolished by guanine nucleotides. However, membranes from estradiol-treated rats demonstrated only low affinity agonist binding that was unaffected by guanine nucleotides. Estradiol did not detectably alter concentrations of either cholera or pertussis toxin substrates in hypothalamus-preoptic area membranes. These data indicate that estrogen promotes a stable time-dependent desensitization of beta-adrenergic receptor activation of adenylyl cyclase in hypothalamus and preoptic area by uncoupling the receptor from the guanine nucleotide-binding protein, G8.

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.

Effects of changing contingencies on the behavior of depressed and nondepressed individuals

The effects of rules versus shaping on the behavior of depressed and nondepressed individuals were compared. Extending the findings in the depressive realism literature to a learning paradigm, the behavior of depressed individuals was more sensitive to changing contingencies than was the behavior of nondepressed individuals. Contrary to hypotheses, however, this effect appeared due primarily to the nondepressive Ss' strategy of continuing to follow an experimenter's inaccurate rules. Results suggest the relative absence of self-presentational concerns may lead depressed individuals to be more accurate in judging environmental contingencies.

Infant onset subacute necrotizing encephalomyelopathy (Leigh's disease)

We reviewed six cases of proven or probable subacute necrotizing encephalomyelopathy with an onset under 12 months of age. All children had been investigated at the Adelaide Children's Hospital in the period 1975-90. Seizures (five of six) and cortical blindness (five of six) were more prominent clinical features at presentation than the literature would suggest, while respiratory abnormalities and developmental delay were also frequent. Flash visual evoked responses, brain-stem auditory evoked responses, and the interictal electroencephalogram did not contributed to diagnosis. Computerized tomography brain scans were abnormal in three of four cases with typical basal ganglia lesions in one case and brain atrophy in two cases. The diagnosis was suspected in four cases with raised blood or cerebrospinal fluid lactate concentrations. The importance of obtaining a blood or cerebrospinal fluid lactate in all infants with unexplained seizures, cortical blindness or apnoea is emphasized.

Purification and separation of holo- and apo-forms of Saccharopolyspora erythraea acyl-carrier protein released from recombinant Escherichia coli by freezing and thawing

Saccharopolyspora erythraea acyl-carrier protein, highly expressed from a T7-based expression plasmid in Escherichia coli, can be selectively released from the cells in near-quantitative yield by a single cycle of freezing and thawing in a neutral buffer. Electrospray mass spectrometry was used to confirm that the recombinant S. erythraea acyl-carrier protein over-expressed in E. coli is present predominantly as the holo-form, with variable amounts of apo-acyl-carrier protein, holo-acyl-carrier protein dimer and holo-acyl-carrier protein glutathione adduct. The holo- and apo-acyl-carrier proteins are both readily purified on a large scale from the freeze-thaw extracts and can be separated from one another by octyl-Sepharose chromatography. The holo-acyl-carrier protein obtained in this way was fully active in supporting the synthesis of acyl-acyl-carrier protein by extracts of S. erythraea.

Direct coupling of opioid receptors to both stimulatory and inhibitory guanine nucleotide-binding proteins in F-11 neuroblastoma-sensory neuron hybrid cells

Evidence is presented for linkage of opioid receptors directly to the stimulatory G protein (guanine nucleotide-binding protein), Gs, in addition to the generally accepted linkage to the inhibitory and "other" G proteins, gi and Go, in F-11 (neuroblastoma-dorsal root ganglion neuron) hybrid cells. Treatment of intact F-11 cells with cholera toxin decreased specific binding of the opioid agonist [D-Ala2,D-Leu5]enkephalin to F-11 cell membranes by 35%, with the remaining binding retaining high affinity for agonist. Under these conditions cholera toxin influenced the alpha subunit of Gs (Gs alpha) but had no effect on the alpha subunit of Gi/o (Gi/o alpha), based on ADP-ribosylation studies. Pertussis toxin treatment decreased high-affinity opioid agonist binding by about 50%; remaining binding was also of high affinity, even though pertussis toxin had inactivated Gi/o alpha selectively and essentially completely. Simultaneous treatment with both toxins had an additive effect, reducing specific binding by about 80%. While opioid agonists inhibited forskolin-stimulated adenylate cyclase activity of F-11 cells as expected, opioids also stimulated basal adenylate cyclase activity, indicative of interaction with Gs as well as Gi. Cholera toxin treatment attenuated opioid-stimulation of basal adenylate cyclase, whereas pertussis toxin treatment enhanced stimulation. In contrast, inhibition by opioid of forskolin-stimulated activity was attenuated by pertussis toxin but not by cholera toxin. It is concluded that a subset of opioid receptors may be linked directly to Gs and thereby mediate stimulation of adenylate cyclase. This Gs-adenylate cyclase interaction is postulated to be responsible for the novel excitatory electrophysiologic responses to opioids found in our previous studies of sensory neurons and F-11 cells.

Clathrin assembly protein AP180: primary structure, domain organization and identification of a clathrin binding site

Binding of AP180 to clathrin triskelia induces their assembly into 60-70 nm coats. The largest rat brain cDNA clone isolated predicts a molecular weight of 91,430 for AP180. Two cDNA clones have an additional small 57 bp insert. The deduced molecular weight agrees with gel filtration results provided the more chaotropic denaturant 6 M guanidinium thiocyanate is substituted for the weaker guanidinium chloride. The sequence and the proteolytic cleavage pattern suggest a three domain structure. The N-terminal 300 residues (pI 8.7) harbour a clathrin binding site. An acidic middle domain (pI 3.6, 450 residues), interrupted by an uncharged alanine rich segment of 59 residues, appears to be responsible for the anomalous physical properties of AP180. The C-terminal domain (166 residues) has a pI of 10.4. AP180 mRNA is restricted to neuronal sources. AP180 shows no significant homology to known clathrin binding proteins, but is nearly identical to a mouse phosphoprotein (F1-20). This protein, localized to synaptic termini, has so far been of unknown function.

Opposing influences of dexamethasone and retinoic acid on adenylate cyclase activity in ROS 17/2.8 cells

Exposure of ROS 17/2.8 cells to dexamethasone (DEX) or retinoic acid (RA) increases and decreases, respectively, adenylate cyclase activity (ACA) in response to isoproterenol, forskolin, guanylylimidodiphosphate, or NaFl. Despite dramatic changes in ACA, there were no significant changes in levels of cholera toxin- or pertussis toxin (PT)-dependent ADP-ribosylation of membranes prepared from cells after DEX or RA exposure as compared to controls. Similarly, immunochemical detection of alpha S, alpha i1-3, and alpha O, as well as Northern blot analysis of messenger RNA for each of the respective GTP binding proteins, also failed to demonstrate an influence of DEX or RA when contrasted with controls. In a novel use of the cyc- reconstitution assay, wherein the influence of inhibitory guanine nucleotide binding proteins in the extracts of control, DEX-, and RA-treated membranes is removed by a previous 24-h incubation with PT in the intact cell, we demonstrate that this PT treatment markedly enhances ACA in the cyc- reconstitution assay for all three preparations, but that the fold-increase due to PT-treatment is greatest in RA-treated cells. The greater magnitude of the effect of PT on RA-treated ROS 17/2.8 cells, in the absence of any obvious quantitative changes in the levels of the PT substrates, suggests that the effect of RA on ROS 17/2.8 cells appears to be an augmentation of the influence of inhibitory guanine nucleotide binding proteins, ultimately leading to reduced ACA.

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.

Clathrin-coated vesicles in nervous tissue are involved primarily in synaptic vesicle recycling

The recycling of synaptic vesicles in nerve terminals is thought to involve clathrin-coated vesicles. However, the properties of nerve terminal coated vesicles have not been characterized. Starting from a preparation of purified nerve terminals obtained from rat brain, we isolated clathrin-coated vesicles by a series of differential and density gradient centrifugation steps. The enrichment of coated vesicles during fractionation was monitored by EM. The final fraction consisted of greater than 90% of coated vesicles, with only negligible contamination by synaptic vesicles. Control experiments revealed that the contribution by coated vesicles derived from the axo-dendritic region or from nonneuronal cells is minimal. The membrane composition of nerve terminal-derived coated vesicles was very similar to that of synaptic vesicles, containing the membrane proteins synaptophysin, synaptotagmin, p29, synaptobrevin and the 116-kD subunit of the vacuolar proton pump, in similar stoichiometric ratios. The small GTP-binding protein rab3A was absent, probably reflecting its dissociation from synaptic vesicles during endocytosis. Immunogold EM revealed that virtually all coated vesicles carried synaptic vesicle proteins, demonstrating that the contribution by coated vesicles derived from other membrane traffic pathways is negligible. Coated vesicles isolated from the whole brain exhibited a similar composition, most of them carrying synaptic vesicle proteins. This indicates that in nervous tissue, coated vesicles function predominantly in the synaptic vesicle pathway. Nerve terminal-derived coated vesicles contained AP-2 adaptor complexes, which is in agreement with their plasmalemmal origin. Furthermore, the neuron-specific coat proteins AP 180 and auxilin, as well as the alpha a1 and alpha c1-adaptins, were enriched in this fraction, suggesting a function for these coat proteins in synaptic vesicle recycling.

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.

Hypoxia-induced increased permeability of endothelial monolayers occurs through lowering of cellular cAMP levels

Prolonged exposure to hypoxia, as at high altitude, results in increased vascular permeability that may be ameliorated by administration of glucocorticoids. To understand mechanisms underlying these observations, cultured bovine aortic and pulmonary artery endothelial cells (ECs) were subjected to hypoxia, and changes in monolayer permeability and adenosine 3',5'-cyclic monophosphate (cAMP) levels were assessed. Exposure of both types of cultured ECs to hypoxia (PO2 approximately 14 Torr) led to a time- and dose-dependent increase in monolayer permeability, as measured by diffusion of radiolabeled solutes, which was associated with a progressive decrease in EC cAMP levels from 60 to 15 pmol/mg protein, and a decrease in EC adenylate cyclase activity. The change in endothelial barrier function was prevented by addition of cAMP analogues. Pertussis toxin protected EC monolayers from hypoxia-mediated increase in permeability while maintaining cAMP levels and adenylate cyclase activity. Addition of dexamethasone to EC monolayers before or simultaneously with their incubation under hypoxic conditions blocked the hypoxia-mediated increase in monolayer permeability. Dexamethasone pretreatment also prevented the decline in cAMP and adenylate cyclase levels in oxygen-deprived cultures. These data indicate that hypoxia decreases EC barrier function by lowering adenylate cyclase activity and cellular cAMP levels. They suggest that dexamethasone may exert its protective effect, in part, by preventing the hypoxia-induced decline in adenylate cyclase activity, leading to an increase in cellular cAMP and maintenance of EC barrier function.

Trypanosoma cruzi: alteration of cAMP metabolism following infection of human endothelial cells

We have previously reported that Trypanosoma cruzi infection of endothelial cells results in alterations in the metabolism of Ca2+, inositol triphosphate (IP3), and prostacycline (PGI2). In this report, we demonstrate that infection also alters the metabolism of cAMP. Infection of endothelial cells does not significantly alter beta-adrenergic receptor density or affinity, adenylate cyclase activity, and whole-cell cAMP levels. However, incubation of infected endothelial cells with the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX) resulted in less than a 60% increase in cell cAMP in contrast to the greater than a 100% increase observed in uninfected endothelial cells under otherwise identical reaction conditions. Infected endothelial cells demonstrated a twofold increase in phosphodiesterase activity when measured directly. Moreover, homogenates prepared from infected endothelial cells previously incubated with isoproterenol for 20 min showed little or no change in PDE activity. In contrast, homogenates prepared from uninfected endothelial cells treated under otherwise identical reaction conditions showed a 5.7-fold increase in PDE activity. In the presence of IBMX, isoproterenol-dependent stimulation of cAMP levels in infected endothelial cells reached a maximum level at 5 min of incubation, and thereafter rapidly declined. In contrast, cAMP levels in uninfected endothelial cells reached a maximum at 2 min of incubation, and thereafter remained elevated throughout the duration of the incubation. Infection-associated changes in isoproterenol dependent stimulation of cAMP accumulation appear to relate, in part, to changes in PDE activity.

The influence of detergents on the availability of pertussis toxin substrates

Pertussis toxin-dependent ADP-ribosylation of rat heart and human mononuclear leukocyte membranes was found to be markedly enhanced in the presence of detergents. The order of potency for this effect of detergents was Triton X-100 approximately Lubrol PX greater than digitonin much greater than cholate greater than 3-[(3-cholamidopropyl)dimethylammonia]propanesulfonic acid. Exposure of membranes to increasing concentrations of detergents increased the proportion of pertussis toxin substrate demonstrable in the supernatant fraction whereas the substrate remaining in the pellet fraction demonstrated a complicated relationship with the concentration of detergent. In complementary experiments, it was found that immunochemical detection of G proteins in the pellet fraction from suspensions previously incubated with a maximal concentration of detergent revealed a reduced presence of G proteins with a concomitant increase in the concentration of G proteins in the supernatant fraction; this situation was not observed at submaximal concentrations of detergent during the preincubation of myocardial membranes. The results suggest that the detergent-mediated enhancement of pertussis toxin's action to ADP-ribosylate susceptible G proteins is a complicated process that includes concentration-dependent creation of conditions favorable to the actions of the toxin as well as solubilization of the substrates for the toxin.

Myocardial beta-adrenergic adenylate cyclase complex in a canine model of chagasic cardiomyopathy

Infection of beagles with an opossum-derived strain of Trypanosoma cruzi (Tc-O) results in features of early and chronic chagasic cardiomyopathy, that is, increases in PR interval, atrioventricular block, and frequent ventricular premature contractions, ventricular tachycardia, and decreased left ventricular ejection fraction. These signs are not observed in animals infected with a canine strain of T. cruzi (Tc-D). To understand the biochemical basis for these early cardiac effects, we examined the beta-adrenergic adenylate cyclase complex in myocardial membranes prepared from animals infected with either of the two strains. In animals infected with Tc-O (symptomatic), the maximum velocity (Vmax) decreased and concentration of agonist resulting in 50% of Vmax (Kact) increased for isoproterenol-dependent adenylate cyclase activity; in animals infected with Tc-D (asymptomatic), Vmax and Kact for isoproterenol were unchanged from control, uninfected animals. beta-Receptor density decreased by 20% in symptomatic animals with no change in affinity, whereas no differences were observed between uninfected and infected asymptomatic animals. A complex pattern of changes was apparent in the guanine nucleotide binding protein, Gs, in the setting of infection. Alterations in cholera toxin-dependent ADP-ribosylation patterns as well as immunochemical detection with anti-G alpha s antisera suggested a change in the biochemical nature of the Gs species and not necessarily a physical loss of this protein. Reconstitution of adenylate cyclase activity in cyc- membranes demonstrated a decrease in hormone-sensitive Gs activity in membranes prepared from symptomatic animals without a change in activity demonstrable in the presence of Gpp(NH)p. Collectively, the results suggest that the depression in beta-adrenergic adenylate cyclase activity associated with symptomatic infection of beagles with T. cruzi occurs primarily as a result of changes in the Gs protein complex, most likely resulting in an uncoupling of the beta-adrenergic receptor from the Gs protein.

Modulation of host cell metabolism by Trypanosoma cruzi

Chagas disease, caused by the hemoflagellate Trypanosoma cruzi, is a complicated and devastating disease. It is hypothesized that an important target of infection may be the endothelial cell and that both the acute and chronic forms of the disease involve abnormalities in the microcirculation. Stephen Morris and colleagues suggest that endothelial cell dysfunction occurs as a consequence of amastigote-associated interference in host cell metabolism.

Pathophysiological insights into the cardiomyopathy of Chagas' disease

The evidence gained from both human and animal studies of chronic chagasic cardiomyopathy suggests that the disease occurs as a consequence of several discrete and progressive pathophysiological processes occurring after infection, the ultimate expression of which depends on a host of unidentified factors. Collectively, the infection-associated events compromise microvasculature function and result in hypoperfusion, with consequences indistinguishable from those observed in other, nonparasitological cardiomyopathic diseases secondary to hypoperfusion. Therefore, chronic chagasic cardiomyopathy may share similar pathophysiological abnormalities with other chronic congestive cardiomyopathic states.

Extracellular matrix derived from Trypanosoma cruzi infected endothelial cells directs phenotypic expression

Infection of confluent human umbilical vein endothelial cells by the parasite Trypanosoma cruzi results in the appearance of an altered heparan sulfate proteoglycan (HSPG) isolated from the extracellular matrix of infected endothelial cells (ECMi). HSPG from ECMi differed from HSPG obtained from the extracellular matrix of uninfected endothelial cells (ECMu) by virtue of an 8-10-fold increase in sulfation and a different elution pattern using DEAE Sepharose chromatography. Analysis of the HSPG that binds to acidic fibroblast growth factor (aFGF) revealed that infection increased the proportion of HSPG that binds to aFGF by 35%. Heparitinase and alkaline borohydride treatment of aFGF-binding HSPG and chromatographic resolution on Sepharose CL4B column revealed an infection-associated 10-fold increase in sulfation of the GAG side chain with no significant change in the migration of the core protein. In addition, the aFGF binding HSPG isolated from ECMi demonstrated a markedly attenuated synergistic mitogenic activity with aFGF in a cell proliferation assay. All of the infection associated changes in HSPG could be demonstrated in HSPG obtained from uninfected endothelial cell cultures grown on ECMi. Hence, the ECMi is associated with signals capable of modulating the ECM associated metabolism of uninfected endothelial cells. This facility of ECMi was also shown to extend to patterns of Gs protein synthesis as revealed by Western blot analysis. The observation that the ECM produced by infected endothelial cells can direct the synthetic patterns of uninfected endothelial cells in a manner uniquely observed in infected endothelial cells suggests a plausible pathway by which infection of only a few cells can ultimately result in the coordinate responses of neighboring uninfected cells.

Enhanced platelet adherence and aggregation in Chagas' disease: a potential pathogenic mechanism for cardiomyopathy

Spasm and thrombosis of the coronary microcirculation has been implicated in the pathogenesis of the cardiomyopathy of Chagas' disease. We demonstrate that increases in platelet adherence and aggregation accompany Trypanosoma cruzi infection and may contribute to the observed microvascular pathology. Scanning electron microscopy and radiolabeled platelets studies revealed that platelet adherence to T. cruzi-infected human endothelial cells was significantly increased when compared to controls (P = 0.024). In in vitro experiments, we determined the influence of infection on prostacyclin production, a marker of endothelial cell perturbation. The basal levels of 6-keto-prostaglandin F1 alpha was significantly greater in the supernatant of infected endothelial cells than in those of uninfected endothelial cells (P less than 0.05). The influence of infection was assessed on platelet aggregation at days 5 and 12 post-infection in A/J mice. Platelets from T. cruzi-infected mice were 2-6-fold more sensitive to aggregation induced by adenosine diphosphate and sodium arachidonate than controls. Thromboxane B2 levels in the plasma of infected mice were greater than controls. These data support the hypothesis that heightened platelet reactivity and endothelial cell dysfunction are associated with acute Chagas' disease and may cause coronary microvascular spasm and/or occlusion.

Analysis of 100-180-kDa phosphoproteins in clathrin-coated vesicles from bovine brain

Protein kinases which co-purify with clathrin-coated vesicles are known to phosphorylate in vitro the 50-kDa subunit of the HA-II adaptor complex and upon inclusion of polylysine the beta-light chain of clathrin and polypeptides above 100 kDa. Here we relate the high molecular mass phosphoproteins to the known subunits of the adaptor protein complexes and to other clathrin-associated proteins by means of immunoprecipitation with monoclonal antibodies, two-dimensional electrophoresis, or electrophoresis in urea-sodium dodecyl sulfate-polyacrylamide gels. Our results show that some of the labeling of the 100-120-kDa region is accounted for by the beta'- and gamma-subunits of the HA-I adaptor complex, the alpha a-, and, to a lesser extent, by the beta-subunits of the HA-II adaptor complex. In addition, we found the assembly protein AP 180 and a hitherto undescribed 110-kDa coat polypeptide to be heavily phosphorylated upon release of these proteins from the coated vesicle membrane. In all cases, labeling was confined to serine residues.

Effect of verapamil on the development of chronic experimental Chagas' disease

In previous work, we have shown that the chronic administration of verapamil, a calcium channel blocker, ameliorated the mortality, pathology, and biochemical alterations associated with acute murine Chagas' disease. To extend these studies to an established chronic model, C3H/Hej mice were infected with the Sylvio X10/4 clone. This clone does not cause symptomatic acute disease but does induce cardiac pathology incorporating several pathological features of human chagasic cardiomyopathy. Cardiac pathology was assessed at 60, 90, and 180 days postinfection. There was a significant decrease in the degree of inflammation and fibrosis in the group infected and treated with verapamil. Myocardial beta-adrenergic adenylate cyclase (AC) activity was determined 180 days postinfection. In the infected group not treated with verapamil, there was no significant change in the maximum rate of conversion of ATP to cAMP (Vmax) or in the concentration of agonist giving 50% of Vmax (apparent Kact) for isoproterenol (ISPN)-dependent AC activation. The increase in Vmax for ISPN determined in the presence of 5'-guanylylimidodiphosphate (Gpp[NH]p) was consistently lower in infected than in uninfected mice, suggesting that infection altered the potential synergistic activation of AC by the guanine nucleotide. In the infected group treated with verapamil, there was a slight increase in the Vmax for ISPN. However, there was a marked enhancement of the synergistic contribution of Gpp(NH)p. These observations suggest that verapamil had preserved that aspect of the AC complex mediating guanine nucleotide sensitive activation of AC. Collectively, the observations in the acute and chronic models of murine Chagas' disease suggest that verapamil may be a useful adjunct in treatment.

Trypanosoma cruzi: infection of cultured human endothelial cells alters inositol phosphate synthesis

Infection of cultured endothelial cells with Trypanosoma cruzi alters intracellular Ca2+ homeostasis. To help understand the biochemical basis for this phenomenon, we determined the influence of infection on inositol phosphate formation in a broken cell preparation. Inositol phosphates participate in the regulation of cytosolic Ca2+. In uninfected endothelial cells, bradykinin guanosine 5'-O-thiophosphate (GTP tau S), and calcium all stimulated inositol phosphate (IP1), inositol bisphosphate (IP2), and inositol trisphosphate (IP3) formation within 5 sec of incubation. At longer periods of incubation with GTP tau S and bradykinin, formation of IP1 was linear for 30 sec, whereas the rate of IP2 and IP3 generation was maximal at 20 and 5 sec, respectively. Second, infection markedly changed these aspects of inositol phosphate generation. First, unstimulated (basal) levels of IP1 and IP3 were markedly increased over those levels in membranes of uninfected cells. Infection decreased the rate of formation for the three inositol phosphates in response to GTP tau S and bradykinin. Finally, infection diminished the magnitude of inositol phosphate synthesis in response to Ca2+ for IP1, IP2, and IP3, respectively. Studies on G proteins using cholera and pertussis toxin were carried out to determine if the infection-associated changes in inositol phosphate generation could be attributed to functional changes in these regulatory proteins known to participate in the activation of phospholipase C. Infection markedly decreased the magnitude of cholera and pertussis toxin-dependent ADP ribosylation, as compared to control uninfected cells. Incubation of uninfected endothelial cells with cholera and pertussis toxin also decreased the magnitude of cholera and pertussis toxin ADP ribosylation. Despite the similar effects of infection and toxin treatment on subsequent toxin-catalyzed ADP ribosylation, toxin treatment did not influence inositol phosphate generation. Collectively, these results demonstrate an influence of infection on receptor-dependent and -independent synthesis of inositol phosphates, possibly by an action on phospholipase C. The results help to explain the apparent infection-associated increase in basal Ca2+ previously observed and suggest that interference with signal transduction may be a consequence of the presence of the parasite.

Ultracentrifugal analysis of the junction complexes of the red cell membrane cytoskeletal network: application to hereditary spherocytosis and metabolically depleted cells

A method has been developed for the assessment of the number of spectrin dimer units associated with each actin protofilament junction, in the membrane cytoskeletal network (i.e. the degree of branching) of the red cell. Ghosts are first exposed to elevated temperature at low ionic strength to dissociate some 65% of the spectrin tetramers (that link the network junctions) into dimers, without causing their release from the actin filaments. Non-ionic detergent is then added to solubilize the membrane itself with its intrinsic proteins, so as to liberate the cytoskeletal material, and the mixture is immediately examined in the analytical ultracentrifuge. The predominant components observed are isolated junctions (20 S), free spectrin dimers and the residual undissociated cytoskeletal material, with very minor components, probably corresponding to multiple junctions, linked by spectrin tetramers. The junction boundary is homogeneous within the accuracy of measurement and is taken to correspond to a complex containing six spectrin dimers, known to predominate in situ. About 17% of the total network is liberated in this form and 12% as free spectrin dimers. In hereditary spherocytosis both the size of the junction complex (as reflected by its sedimentation coefficient) and the proportion of the complex and of free spectrin liberated are indistinguishable from normal values. We conclude that the reported deficit of spectrin in hereditary spherocytosis is not reflected by a lower degree of branching of the network, and, if the membrane area is not correspondingly reduced, this must mean that the junctions are more widely spaced and the spectrin tetramers therefore more extended. In metabolically depleted cells, in which the cytoskeletal proteins are known to be extensively dephosphorylated, there is no change in the sedimentation pattern and thus no detectable loss of spectrin from the junctions or weakening in the cohesion of the cytoskeletal network.

Verapamil ameliorates clinical, pathologic and biochemical manifestations of experimental chagasic cardiomyopathy in mice

The influence of long-term verapamil administration on the consequences of Trypanosoma cruzi infection in mice was studied with regard to animal mortality, morbidity, myocardial pathologic features and myocardial beta-adrenergic adenylate cyclase activity. Verapamil administration dramatically decreased the mortality rate from 60% to 6% during the 70 day period of infection. Three clinical stages of infection were evident. In the acute stage (17 days after infection with maximal parasitemia), verapamil treatment not only decreased the incidence of myocardial disease (fibrosis and inflammation), but also protected myocardial beta-adrenergic adenylate cyclase activity. In addition, there was no increase in total body weight, which was regarded as an index of right-sided heart failure. In the subacute stage (30 to 60 days after infection), administration of verapamil continued to decrease myocardial disease and preserve beta-adrenergic adenylate cyclase activity. In addition, verapamil ameliorated the morbidity and mortality associated with this stage of infection. The chronic stage of infection was characterized by a decrease in myocardial disease and in beta-adrenergic adenylate cyclase activity. Thus, independent of the state of infection, long-term verapamil treatment enhanced beta-adrenergic adenylate cyclase activity. In addition, verapamil ameliorated the morbidity associated with infection. Although the relation among these various effects of verapamil in the setting of T. cruzi infection remains to be determined, collectively the results suggested that verapamil administration attenuated the consequences of T. cruzi infection.

Composition of the ternary protein complex of the red cell membrane cytoskeleton

The red cell membrane skeletal network is constructed from actin, spectrin and protein 4.1 in a molar ratio of actin subunits/spectrin heterodimer/protein 4.1 of 2:1:1. This represents saturation of the actin filaments, since incubation with extraneous spectrin and protein 4.1 leads to no binding of additional spectrin, either to the inner surface of ghost membranes or to lipid-free membrane cytoskeletons. Partial extraction of spectrin from the membrane is accompanied by release of actin under all conditions. Regardless of the proportion of spectrin extracted, the molar ratio of spectrin dimers/actin subunits is constant at 1:2. This is not the result of release or cooperative breakdown of whole lattice junctions from the network, for the number of actin filaments, judged by capacity to nucleate polymerisation of added G-actin, remains unchanged even when as much as 60% of the total spectrin has been lost. A similar 1:2:1 stoichiometry characterises the complex formed when G-actin is allowed to polymerise in the presence of varying amounts of spectrin and protein 4.1. When this complex is treated with the depolymerising agent, 1 M guanidine hydrochloride, it breaks down into smaller units of the same stoichiometry. After cross-linking these can be recovered from a gel-filtration column. Complexes prepared starting from G-actin appear to be much more stable than those formed when spectrin and protein 4.1 are bound to F-actin.

Structural basis for the high activation energy of spectrin self-association

The association of spectrin hetero-dimer (alpha beta) to the tetramer (alpha 2 beta 2, which predominates in the cell) is marked by an exceptionally high activation energy, so that the reaction does not proceed measurably in the cold. We have tested the hypothesis that this is due to intra-dimer association between the alpha- and beta-chain ends, which must be broken before tetramers can form. Two mutant univalent spectrins with association defects at the alpha and beta ends, respectively, and incapable therefore of intra-dimer bonding, were found to associate rapidly with one another at 4 degrees C. The bimolecular rate constant is greater than for the association of normal dimers by 6 orders of magnitude.

Rapid purification of clathrin-coated vesicles by free-flow electrophoresis

Free-flow electrophoresis was successfully used as the final step in the purification of clathrin-coated vesicles from bovine brain. Based on biochemical analysis, the material obtained in this way was found to be of equal purity with respect to the protein composition and lipid content as that purified by the previously widely used methods of permeation chromatography on controlled pore glass or Sephacryl S-1000. However, as judged by electron microscopy, the electrophoretically purified coated vesicles contained less smooth membranes than the coated vesicle preparations that had been obtained by permeation chromatography. Free-flow electrophoresis offers considerable advantages in speed of purification, in the total amount of material processed and in flexibility of operation. Analysis of the electrophoretic mobility of purified coated vesicles showed that this is governed by the coat proteins rather than by the vesicle contained therein. A shift in electrophoretic mobility of purified coated vesicles was obtained by the binding of coat protein specific monoclonal antibodies. This raises the possibility of purifying subpopulations of coated vesicles with respect to coat protein composition.

Origin of mutation in neoplasia

A hypothesis is presented relating the origin of somatic mutation in neoplasia to intrinsic rates of mitotic error. This implies that the environmental agents which are significant in clinical neoplasia are promoters and mitogenic. The tumorigenic mutations may involve genes which are important in cellular differentiation and senescence of dividing cells.

Alterations in intracellular calcium following infection of human endothelial cells with Trypanosoma cruzi

Trypanosoma cruzi infection in cultured human umbilical vein endothelial cells increased basal cellular calcium levels from 55 to 110 nM, as monitored with the fluorescent probe, fura-2. It also influenced intracellular calcium such that consistently higher total levels were observed in response to bradykinin, angiotensin II and norepinephrine, as compared to similarly treated uninfected cells. However, bradykinin and angiotensin II-dependent increases in calcium, when considered as the absolute increment or fold elevation over basal, were significantly lower in infected endothelial cells. Infection also influenced changes in calcium levels due to agents that operate independently of plasma membrane receptors. In the presence of ionomycin, the magnitude and rate of rise of intracellular calcium were decreased; additionally the calcium peak was delayed and the subsequent decline slowed. Similar to the results with bradykinin and angiotensin II, infection decreased both the increment in and fold stimulation of intracellular calcium in response to ionomycin. In contrast, infection altered only the total calcium stimulated in response to oligomycin; neither the fold stimulation of, nor increment in intracellular calcium was affected. These results indicate that (1) infection by T. cruzi alters calcium homeostasis in endothelial cells under basal and stimulated conditions; (2) both receptor-dependent and receptor-independent mechanisms are affected by infection. The possible contribution of altered calcium homeostasis induced by T. cruzi in the pathogenesis of chagasic cardiomyopathy is considered.

Myocardial adenylate cyclase activity in acute murine Chagas' disease

We have studied the influence of myocardial infection with Trypanosoma cruzi on the beta-adrenergic adenylate cyclase complex in mouse myocardial membranes. The maximal rate of cAMP generation (Vmax) and the concentration of agonist associated with 50% of the maximal activity (apparent Kact) were determined for a series of agents. Six days after infection, the Vmax for isoproterenol significantly declines without a change in the apparent Kact. After 21 days of infection, both the Vmax and apparent Kact for isoproterenol are reduced. At 6 and 21 days of infection, the affinity of the beta-receptor for [125I]iodocyanopindolol declines from 0.84 to 3.6 and 3 nM, respectively, while the receptor density increases with the duration of infection from 33 to 57 and 82 fmol/mg protein, respectively. The Vmax (but not the apparent Kact) for forskolin and Mg2+- and Mn2+-associated activities declines also after 21 days. Another adenylate cyclase activity, which was stimulated by the nonhydrolyzable guanine nucleotide Gpp(NH)p, declines in relation to the duration of infection. Inhibitors of adenylate cyclase activity were also studied. Inhibition of adenylate cyclase activity by adenosine and by Gpp(NH)p (in the presence of forskolin) declines after 21 days of infection. The results suggested that the coupling proteins Ns and Ni, which mediate stimulatory or inhibitory control of receptors to adenylate cyclase activity, might be altered by infection. As monitored by cholera toxin- and pertussis toxin-dependent ADP ribosylation of their respective substrates, which include Ns and Ni proteins, respectively, there are declines in the availability of both substrates as a result of T. cruzi infection. For infected membranes, the addition of NADP enhances the magnitude of cholera toxin-dependent ADP ribosylation and renders the magnitude of pertussis toxin-dependent ADP ribosylation equal to that observed in uninfected membranes. The results support the hypothesis that infection with T. cruzi results in profound generalized alterations of the adenylate cyclase complex at several different sites.

Interactions of spectrin in hereditary elliptocytes containing truncated spectrin beta-chains

An abnormal spectrin, in which one subunit is truncated, has been detected in a large German family. The inheritance is autosomal dominant. The affected members of the family suffer in widely varying degree from a microcytic hemolytic anemia. The red cell morphology varies correspondingly from smooth elliptocytes to predominantly poikilocytes. The abnormal spectrin makes up approximately 30% of the total and is almost entirely present as the dimer. The truncated chain is not phosphorylated by the endogenous cAMP-independent kinase, and it has been identified as a chain of beta-type, using monoclonal antibodies. Because a univalent terminal spectrin alpha-chain fragment will bind to normal dimers with an association constant lower by only a factor of two than that for the self-association of the dimers, it would be expected that the mutant dimers (alpha beta') would readily enter into an association with normal (alpha beta) dimers to give alpha 2 beta beta' tetramers (though not with each other). In dilute solution this is indeed observed, and the diminution in tetramer concentration when 30% of normal spectrin is replaced by alpha beta' dimers, amounts to only a small proportion. Moreover, in the membrane skeleton, if there is pairwise apposition of dimer units, only 9% of pairings will be between units that cannot associate. We have shown that the failure of alpha beta' dimers to enter into heterologous associations in situ is not due to the elimination of the ankyrin binding site near the truncated end of the beta-chain: this site is fully functional, as judged by rebinding to spectrin-depleted vesicles. When the spectrin is extracted from the membrane in the cold, the material released initially consists almost entirely of alpha beta' dimers; when the spectrin of normal membranes is partly dissociated to dimers in situ by warming at low ionic strength, extraction in the cold then leads similarly to much more rapid release of the dimer than of the tetramer. The similar rates of liberation of normal and abnormal dimer make it unlikely that the interaction of the latter with the membrane is in any way defective. When mixtures of alpha beta and alpha beta' dimers are bound to spectrin-depleted inside-out membrane vesicles from normal cells and tetramers are allowed to form by equilibration at 30 degrees C, the proportion of the abnormal species appearing in the tetramer is much lower than would be expected on a statistical basis. The relation of the self-association equilibrium on the membrane to that of spectrin in dilute solution is analyzed.

The influence of EDTA on adenylate cyclase activity in membranes from rat and mouse myocardium

Inclusion of EDTA in the homogenization buffer of both mouse and rat myocardium profoundly alters the properties of the adenylate cyclase complex. EDTA leads to an increase in the Vmax for adenylate cyclase activity due to all of the following agents: isoproterenol, Gpp[NH]p, forskolin and Mg2+. For forskolin and Mg2+, the EDTA-associated increase in Vmax is not accompanied by a change in sensitivity to activation. However, EDTA is associated with enhanced sensitivity to activation by isoproterenol and increased sensitivity to the effect of Mg2+ on isoproterenol-dependent adenylate cyclase activity. A result of greater isoproterenol-dependent adenylate cyclase activity, due to the presence of EDTA, is an attenuated synergistic contribution of Gpp[NH]p. Changes in stimulatable adenylate cyclase activity as a result of EDTA occurs in concert with effects of cholera toxin upon ADPribosylation of the guanine nucleotide regulatory protein, Ns. Substantial auto-ADP-ribosylation occurs in a cholera toxin-sensitive 42 kDa band in membranes prepared in the presence of EDTA. In addition, cofactor and substrate requirements in the cholera toxin-dependent ADP-ribosylation reaction depend on the method of membrane preparation. The results suggest that the integrity of the adenylate cyclase complex depends in part on the attention given to proteolysis that may be activated during the course of homogenization.

Infection of L6E9 myoblasts with Trypanosoma cruzi alters adenylate cyclase activity and guanine nucleotide binding proteins

We studied the consequences of infection of L6E9 myoblasts with T. cruzi on the adenylate cyclase complex to test the hypothesis that infection alters the functional properties of the guanine nucleotide regulatory proteins, Ns and Ni. Stimulating activities of adenylate cyclase due to isoproterenol, isoproterenol plus Gpp(NH)p, or forskolin (activities mediated by Ns) are not altered by infection. However, inhibitory activities mediated by Ni [Gpp(NH)p, acetylcholine, and adenosine inhibition of forskolin-dependent adenylate cyclase activity] are compromised by infection. The reduction in adenosine's inhibition of forskolin-dependent adenylate cyclase activity is seen throughout the effective concentration range of adenosine. Pertussis toxin does not change basal or stimulated adenylate cyclase activity in infected cells compared with normal uninfected cells, nor does it alter the inhibiting action of adenosine. To evaluate the coupling proteins (Ns and Ni) involved in the stimulation and inhibition of adenylate cyclase more directly, cholera- and pertussis-toxin-dependent ADP ribosylation studies were performed. The incorporation of [32P]ADP ribose in the presence (specific) or absence (nonspecific) of the toxins was markedly decreased in membranes prepared from infected cells. However, in membranes prepared from infected or uninfected cells previously treated with pertussis toxin, there was a significant reduction in specific pertussis-toxin dependent ADP ribosylation. The infection-associated diminution in toxin-dependent ADP ribosylation complements the impaired inhibition of adenylate cyclase data. Collectively, the data further substantiate an infection-associated alteration in the adenylate cyclase complex, probably at the level of the guanine nucleotide binding proteins.

Specificity of sperm-binding Wolffian duct proteins in the rooster and their persistence on spermatozoa in the female host glands

Unlike those of mammals, chicken spermatozoa can develop their fertilizing ability before they leave the testis to pass into the Wolffian duct; moreover, chicken spermatozoa do not require a period of capacitation in the female tract. A question arises, therefore, as to the significance of secretory proteins shown to bind to the surface of chicken spermatozoa as they pass into and through the Wolffian duct. Using anti-Wolffian duct fluid IgG as a probe visualized by immunoperoxidase staining, the present investigation confirms that testicular spermatozoa of quail and turkey as well as chicken do not have any surface determinants in common with those present in Wolffian duct secretions. By contrast, those in the lower portion of the vas deferens display a strong reaction with anti-Wolffian fluid IgG over their entire surface, and immunoprecipitation studies suggest that this reflects the binding of four Wolffian duct proteins. Since a reaction to the antichicken fluid IgG is shown also by mature quail and turkey, but not duck and pigeon spermatozoa, the Wolffian components that coat spermatozoa in birds appear to have a specificity confined to the same order, in this case the Galliformes. Following vaginal or intramagnal insemination, spermatozoa present 48 hours later in the uterovaginal host glands and infundibulum glands, respectively, still reacted strongly. This finding that Wolffian duct components persist on the surface of spermatozoa in the female tract is consistent with the possibility that they have some role in sperm storage or survival in female birds.