Alzheimer disease amyloid beta protein forms calcium channels in bilayer membranes: blockade by tromethamine and aluminum

Amyloid beta protein (A beta P) is the 40- to 42-residue polypeptide implicated in the pathogenesis of Alzheimer disease. We have incorporated this peptide into phosphatidylserine liposomes and then fused the liposomes with a planar bilayer. When incorporated into bilayers the A beta P forms channels, which generate linear current-voltage relationships in symmetrical solutions. A permeability ratio, PK/PCl, of 11 for the open A beta P channel was estimated from the reversal potential of the channel current in asymmetrical KCl solutions. The permeability sequence for different cations, estimated from the reversal potential of the A beta P-channel current for each system of asymmetrical solutions, is Pcs > PLi > PCa > or = PK > PNa. A beta P-channel current (either CS+ or Ca2+ as charge carriers) is blocked reversibly by tromethamine (millimolar range) and irreversibly by Al3+ (micromolar range). The inhibition of the A beta P-channel current by these two substances depends on transmembrane potential, suggesting that the mechanism of blockade involves direct interaction between tromethamine (or Al3+) and sites within the A beta P channel. Hitherto, A beta P has been presumed to be neurotoxic. On the basis of the present data we suggest that the channel activity of the polypeptide may be responsible for some or all of its neurotoxic effects. We further propose that a useful strategy for drug discovery for treatment of Alzheimer disease may include screening compounds for their ability to block or otherwise modify A beta P channels.

[Juxtapapillary diverticuli and biliary lithiasis]

Duodenal diverticuli has been associated with biliary stones, specially in the common bile duct. Its presence alters the anatomy of the region of the papilla difficulting its identification and cannulation. ERCP was performed in 800 patients with suspicion of bilio-pancreatic disease, 60 (7.5%) of these patients (39 male and 21 female) had juxtapapillary diverticuli (single diverticuli in 52, 2 in 7 and 3 in 1 patient). In these patient cannulation of the common bile duct was possible in 43 (72%), only the pancreatic duct in 5 (8%) and no cannulation in 12 (20%). Common bile duct stones were found in 22 patients, papillotomy was indicated in 14 patients and was performed in 12, in 2 patients it was not possible to position the papillotomy.

Relationship between the degree of poverty and the IgE response to Ascaris infection in slum children

We examined a group of urban slum children in Caracas, Venezuela, and demonstrated the relationship that exists between poverty, conditions of hygiene and the prevalence of helminth infection. Concordant with the high prevalence of helminth infection in these children, the total serum levels of immunoglobulin E (IgE) and blood eosinophilia were elevated and were directly related to the degree of poverty and lack of sanitary facilities. However, in contrast, the reverse pattern was observed for the specific allergic response to these parasites. Thus, the immediate hypersensitivity skin test reactivity to Ascaris antigens, and the serum levels of specific anti-Ascaris IgE antibody, were lowest in the poorest children, who had the highest prevalence of helminth infection and the highest total IgE levels. As allergic-type reactions may participate in protective mechanisms against helminths, these results suggest that poverty and poor sanitary conditions may, by influencing the IgE response, compromise the resistance of such children to parasitic infections.

Effects of progesterone and estradiol on the proliferation of phytohemagglutinin-stimulated human lymphocytes

In this paper we report on a study to elucidate whether the response of human lymphocytes to mitogenic stimulation was modified by physiological changes which occur during the menstrual cycle. Experiments with untreated cultures showed intra-individual variation to mitogen stimulation in female lymphocyte cultures, but a significant correlation between the menstrual cycle and the proliferation kinetics of lymphocytes was not found. Consequently, we performed experiments in which two of the hormones that regulate the menstrual cycle in women, estradiol and progesterone, were added to cultured human lymphocytes obtained from both men and women. The results indicate that both hormones at physiological concentrations have the capacity to modify the proliferation of PHA-stimulated human lymphocytes. Therefore, both hormones could play a role in the induction of the intra-individual variation observed in the untreated female cultures. However, in vivo other factors could also modify the proliferation kinetics of human lymphocytes preventing the demonstration of the effects of a single factor, such as the hormonal changes occurring during the menstrual cycle.

Calcium-independent K(+)-selective channel from chromaffin granule membranes

Intact adrenal chromaffin granules and purified granule membrane ghosts were allowed to fuse with acidic phospholipid planar bilayer membranes in the presence of Ca2+ (1 mM). From both preparations, we were able to detect a large conductance potassium channel (ca. 160 pS in symmetrical 400 mM K+), which was highly selective for K+ over Na+ (PK/PNa = 11) as estimated from the reversal potential of the channel current. Channel activity was unaffected by charybdotoxin, a blocker of the [Ca2+]-activated K+ channel of large conductance. Furthermore, this channel proved quite different from the previously described channels from other types of secretory vesicle preparations, not only in its selectivity and conductance, but also in its insensitivity to both calcium and potential across the bilayer. We conclude that the chromaffin granule membrane contains a K(+)-selective channel with large conductance. We suggest that the role of this channel may include ion movement during granule assembly or recycling, and do not rule out events leading to exocytosis.

Populations of larvae of anopheles spp. in natural breeding sites in western Venezuela, an area of refractory malaria

Studies have been undertaken into on the diversity and relative abundance of larvae of Anopheles (Nyssorhynchus) spp. in 22 permanent or temporary pools in an area of 70 km2 in the eastern piedmont of the Venezuela Andes, between the mountains and the plains, an area in which malaria is refractory and A. nuñeztovari is present. Twelve species were identified, the most frequent, abundant and sympatric being A. triannulatus, A. albitarsis, A. nuñeztovari, A. oswaldoi and A. strodei. The samples from the permanent pools showed greater diversity of species and greater numbers of larvae than the samples from the temporary pools. The existence of the same larval associations in pools of other localities in the eastern piedmont of the Venezuelan Andes suggests the possibility of the making an ecological map of the breeding sites of A. nuñeztovari and for these anophelines in a region extending for 430 km.

Inorganic arsenic effects on human lymphocyte stimulation and proliferation

Lymphocyte cultures from individuals exposed to high levels of hydroarsenicism showed a slower cell cycle kinetics than cultures from low-exposed individuals. Since this difference in proliferation could be due to chronic arsenic exposure, the in vitro effects of inorganic arsenic in human whole blood lymphocyte cultures were investigated. When lymphocytes were exposed to concentrations of arsenite and arsenate similar to those found in the blood of exposed subjects (10(-7), 10(-8) and 10(-9) M) during the last 24 h before harvesting, a dose-related inhibition of proliferation was observed. Cultures were also treated with 10(-9) M of arsenite and arsenate for 2, 6 and 24 h at the beginning of the cultures in the presence or absence of phytohemagglutinin (PHA). Inhibition of stimulation and proliferation was directly related to the length of treatment. The results show that, at the concentrations tested, arsenite and arsenate impair lymphocyte stimulation and proliferation and confirm the fact that chronic arsenic exposure can affect the proliferation of whole blood lymphocytes.

Are mitotic index and lymphocyte proliferation kinetics reproducible endpoints in genetic toxicology testing?

Lymphocyte proliferation kinetics is an endpoint used in genetic toxicology which has recently been proposed as an alternative for the screening of new cytostatic drugs. Although great variability for this parameter has been reported, there are few reports about the intra- and inter-individual variation of the effects of chemicals on this endpoint. For this reason, experiments were conducted to evaluate the reproducibility of the effects of a well-known cytostatic, mitomycin C (MMC), on the proliferation of PHA-stimulated human lymphocytes, both over time and among samples from several donors. Although inter-individual variability was shown in both parameters in untreated and treated cultures, this variation was not significant. Intra-individual variation was significantly detected only in cultures treated with 0.1 microM MMC.

Integration of cytoplasmic calcium and membrane potential oscillations maintains calcium signaling in pituitary gonadotrophs

Pituitary gonadotrophs exhibit spontaneous low-amplitude fluctuations in cytoplasmic calcium concentration ([Ca2+]i) due to intermittent firing of nifedipine-sensitive action potentials. The hypothalamic neuropeptide, gonadotropin-releasing hormone, terminates such spontaneous [Ca2+]i transients and plasma-membrane electrical activity and initiates high-amplitude [Ca2+]i oscillations and concomitant oscillations in membrane potential (Vm). The onset of agonist-induced [Ca2+]i oscillations is not dependent on Vm or extracellular Ca2+ but is associated with plasma-membrane hyperpolarization interrupted by regular waves of depolarization with firing of action potentials at the peak of each wave. The Vm and Ca2+ oscillations are interdependent during continued gonadotropin-releasing hormone action (greater than 3-5 min), when sustained Ca2+ entry is necessary for the maintenance of [Ca2+]i spiking. The initial and sustained agonist-induced Ca2+ transients and Vm oscillations are abolished by blockade of endoplasmic reticulum Ca(2+)-ATPase, consistent with the role of Ca2+ re-uptake by internal stores in the oscillatory response during both phases. Such a pattern of synchronization of electrical activity and Ca2+ spiking in cells regulated by Ca(2+)-mobilizing receptors shows that the operation of the cytoplasmic oscillator can be integrated with a plasma-membrane oscillator to provide a long-lasting signal during sustained agonist stimulation.

Apamin-sensitive potassium channels mediate agonist-induced oscillations of membrane potential in pituitary gonadotrophs

In cultured rat pituitary gonadotrophs, gonadotropin-releasing hormone (GnRH) induces rapid hyperpolarization of the cell membrane and causes cessation of the spontaneous electrical activity present in non-stimulated cells. This initial response to GnRH is followed by slow oscillations of membrane potential (Vm) which often exhibit brief bursts of action potentials (AP) fired from the peak of the oscillations. The hyperpolarization waves are synchronous with GnRH-induced elevations of cytoplasmic Ca2+ concentration ([Ca2+]i), such that Vm maxima alternate with the peak values of [Ca2+]i. The Vm oscillations result from repetitive activation of apamin-sensitive K+ channels by cytoplasmic Ca2+. Thus, GnRH activation of Ca2+ mobilization can generate a bursting pattern of membrane potential through the activation of K+ channels against a background of spontaneous electrical activity.

Intrinsic anion channel activity of the recombinant first nucleotide binding fold domain of the cystic fibrosis transmembrane regulator protein

The first nucleotide binding fold (NBF-1) from the cystic fibrosis transmembrane regulator (CFTR) has been expressed in bacteria and found to bind ATP and to express anion channel activity when reconstituted onto a planar lipid bilayer. This evidence suggests that the NBF forms the anion-selective portion of the CFTR channel. We also found that the recombinant NBF-1 anion channel is blocked by ATP (1 mM), under which condition it appears to have a minimal conductance of approximately 9 pS and an ohmic current-voltage relationship. We further found that the recombinant NBF-1 bearing the delta F508 mutation has nearly identical anion channel activity to that of the wild-type protein but can be distinguished from wild type under bianionic conditions with chloride and gluconate. We conclude from these data that the anion channel activity of the recombinant NBF-1 could represent all or part of the anion conductance mechanism of CFTR and that the role of the ATP binding by the NBF could be to modulate this anion channel activity.

Quantitative analysis of depolarization-induced ATP release from mouse brain synaptosomes: External calcium dependent and independent processes

We and others have shown previously that ATP is secreted from mouse brain synaptosomes following depolarization of the membrane by high [K+]o and the time course can be monitored accurately by measuring the light emitted from luciferin-luciferase included in the reaction medium. In the present work we have evaluated the relative importance of [Ca2+]o and membrane potential on the ATP secretion process by modelling the time course of ATP release under different conditions. After correction of the records for destruction of released ATP by synaptosomal ecto-ATPase activity, we found that ATP secretion occurs by an apparent first order process. We also established that, in addition to the classical [Ca2+]o-dependent mode, ATP secretion also occurred in the absence of extracellular calcium ([Ca2+]o less than 1 microM). Upon lowering the extracellular Ca2+ concentration, both the rate and the extent of ATP secretion decreased. To assess the contribution of membrane potential to the release rate we measured ATP secretion at membrane potentials determined by extracellular [K+]o (or [Rb+]o) as defined by the distribution of the carbocyanine dye, diSC3(5). Rate constants computed from measured secretion curves revealed that this parameter was essentially independent of membrane potential in the absence of [Ca2+]o. Noise analysis of the light signal showed that the variance increased upon stimulation by high [K+]o, suggesting that both modes of secretion are quantal. Thus, we conclude that the rate of ATP secretion from nerve terminals depends upon Ca2+ entry but not on membrane potential, per se.

[Hematologic values and serum enzymes in horses inoculated with snake venoms for the production of antivenins in Costa Rica]

Blood components were studied in six horses immunized with snake venoms for the production of polyvalent antivenom in Costa Rica. No significant changes in hemoglobin or hematocrit throughout the immunization period were observed, whereas a significant increment in total serum proteins occurred in the second half of the immunization process, probably due to an increased synthesis of immunoglobulins. There were no significant changes in creatine kinase, but a slight increment was detected in both transaminases, although they did not exceed normal limits. These findings suggest the absence of relevant tissue damage in skeletal muscle, cardiac muscle and liver. In agreement with these results, horses did not develop signs of systemic poisoning, presenting only minor alterations at the site of venom injection, such as oedema, abscesses and fistulas. The development of anti-phospholipase A2 antibody response showed a prominent individual variability, as previously described.

Calcium signaling and secretory responses in agonist-stimulated pituitary gonadotrophs

In cultured pituitary gonadotrophs, gonadotropin-releasing hormone (GnRH) caused dose-dependent and biphasic increases in cytoplasmic calcium concentration ([Ca2+]i) and LH release. Both extra- and intracellular calcium pools participate in GnRH-induced elevation of [Ca2+]i and LH secretion. The spike phase of the [Ca2+]i response represents the primary signal derived predominantly from the rapid mobilization of intracellular Ca2+. In contrast, the prolonged phase of the Ca2+ signal depends exclusively on Ca2+ entry from the extracellular pool. The influx of Ca2+ occurs partially through dihydropyridine-sensitive calcium channels. Both [Ca2+]i and LH responses to increasing concentrations of GnRH occur over very similar time scales, suggesting that increasing degrees of receptor occupancy are transduced into amplitude-modulated Ca2+ responses, which in turn activate exocytosis in a linear manner. However, several lines of evidence indicated the complexity over the relationship between Ca2+ signaling and LH exocytosis. In contrast to [Ca2+]i measurements in cell suspension, single cell Ca2+ measurements revealed the existence of a more complicated pattern of Ca2+ response to GnRH, with a biphasic response to high agonist doses and prominent oscillatory responses to lower GnRH concentrations, with a log-linear correlation between GnRH dose and the frequency of Ca2+ spiking. In addition, analysis of the magnitudes of the [Ca2+]i and LH responses of gonadotrophs to a wide range of GnRH concentrations in the presence and absence of extracellular Ca2+, and to K+ and phorbol ester stimulation, showed non-linearity between these parameters with amplification of [Ca2+]i-mediated exocytosis. Studies on cell depleted of protein kinase C under conditions that did not change the LH pool suggested the participation of protein kinase C in this amplification, especially during the plateau phase of the secretory response to GnRH.

Isolation and purification of human biliary vesicles with potent cholesterol-nucleation-promoting activity

1. Cholesterol nucleation is a critical step in the formation of cholesterol gallstones. This nucleation takes place after aggregation and fusion of cholesterol-rich biliary vesicles, a process probably modulated by biliary proteins. The present study was conducted to identify specific proteins associated with native cholesterol-rich biliary vesicles and to explore their effect on the cholesterol-nucleation time of supersaturated artificial bile. 2. Hepatic bile was obtained from six patients with cholesterol gallstone disease. Biliary vesicles were isolated by ultracentrifugation and were purified by gel filtration chromatography. A small amount of protein (less than 1% by weight) remained associated with the purified cholesterol-rich biliary vesicles. The electrophoretic profile of these proteins was remarkably similar in all six patients, showing the presence of at least six polypeptides (of molecular mass from 52 to 200 kDa), five of them having carbohydrate residues (except the 52 kDa one). The effect of reconstituted biliary vesicle solutions, containing their specific vesicular proteins, on cholesterol-nucleation time was studied by mixing the vesicle solution with artificial supersaturated bile. A potent cholesterol-pronucleating activity, reflected in a 20-70% reduction in nucleation time, was present in the biliary vesicle solutions compared with control solutions having a similar lipid composition. The pronucleating activity disappeared on heating and was not detected in the micellar fraction containing the major proportion of biliary proteins. 3. These results indicate that cholesterol-rich biliary vesicles containing a unique and defined glycoprotein profile can be isolated and purified from human hepatic bile. The potent cholesterol-pronucleating activity of the biliary vesicles from patients with gallstones was unrelated to their lipid composition or cholesterol content.(ABSTRACT TRUNCATED AT 250 WORDS)

Bronchoconstriction in helminthic infection

In order to determine whether infection by helminthic parasites can be associated with a state of bronchoconstriction, we evaluated the response to the inhalation of a bronchodilator before and after long-term anthelmintic treatment of children in a urban slum of Caracas, Venezuela. In untreated children, a direct association was found between the degree of helminthic infection and the increase in peak expiratory flow rates caused by the bronchodilator. The elimination of the infections was accompanied by a significant decrease in response to the bronchodilator. These results indicate that helminthic infection could contribute to the development of asthmatic conditions in areas where these parasites are endemic.

[Metacyclics of Leishmania mexicana in the hypopharynx of Lutzomyia youngi experimentally infected]

Although it has been postulated that the natural transmission of leishmaniasis occurs by regurgitation of the parasites from contaminated proboscis of phlebotomine vector recent experimental results seems to oppose this thesis. Wild-caught and laboratory-reared females of Lutzomyia youngi, vector of Leishmania mexicana in the Venezuelan Andes, were infected on tarsal lesion of hamsters, inoculated 6 weeks previously s.c. with 2 x 10(4) amastigotes of L. mexicana s.l., isolated from Venezuelan case of diffuse leishmaniasis. The insects were kept at 23 degrees C and 80% R.H., on a 50% (v:v) solution of "unrefined" cane sugar. The parasites developed through 3 stages: i) differentiation of the amastigotes and exponential growth in the number of promastigotes, ending between 60 and 108 hrs, with a massive fecal elimination of large promastigotes; ii) a stationary phase in growth with flagellar adhesion to the cuticle of the stomodeum and synthesis of a gel that formed a plug between 60 and 120 hrs; iii) differentiation of metacyclics, which invade the hypopharyngeal duct in 7% of the insects, from the 5th day post-infection, and most frequently between the 6th and 9th day. The metacyclics measured 4.2/microns in body length, 1.07/microns in maximum with and the flagellum was 8.8/microns long. The parasites swam freely in the saliva of the hypopharyngeal duct (lumen 6/microns in diameter), from the apex to union with the salivary duct, without invading the latter. Similar results has been obtained in the same vector experimentally infected with other two strains of L. mexicana isolated respectively from wild Lu. flaviscutellata and from another case of diffuse leishmaniasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Endoplasmic reticulum as a source of Ca2+ in neurotransmitter secretion

Depolarization of the synaptosomal membrane by a rapid elevation of [K+]0 induces secretion of adenosine-5'-triphosphate (ATP) as well as the specific neurotransmitters. In addition to the classical [Ca2+]0-dependent mode, we have found that ATP secretion also occurred in the absence of extracellular calcium [( Ca2+]0 less than 1 microM). The extent of both modalities of secretion depended on membrane potential, and the [Ca2+]0-independent secretion proceeded at a rate that was substantially smaller than that of the [Ca2+]0-dependent mode at all membrane potentials examined. We propose that intracellular stores may provide the Ca2+ required for exocytosis in the [Ca2+]0-independent mode of ATP secretion. To test this hypothesis, we searched for the presence of Ca(2+)-release channels gated by intracellular messengers in our synaptosomal preparation. We fused membrane vesicles from lysed synaptosomes with acidic phospholipid bilayers formed at the tip of a patch pipette and found that these membranes contained a Ca(2+)-selective channel. The properties of this channel resemble those of the Ca(2+)-release channel reconstituted from sarcoplasmic reticulum membrane vesicles. These include size of the single open-channel conductance (75 pS Cs+ as the main current carrier), activation by adenine nucleotides (ATP), ryanodine and caffeine, and inhibition by ruthenium red.