The sequential direct and indirect effects of mountain uplift, climatic niche and floral trait evolution on diversification dynamics in an Andean plant clade

Why and how organismal lineages radiate is commonly studied through either assessing abiotic factors (biogeography, geomorphological processes, climate) or biotic factors (traits, interactions). Despite increasing awareness that both abiotic and biotic processes may have important joint effects on diversification dynamics, few attempts have been made to quantify the relative importance and timing of these factors, and their potentially interlinked direct and indirect effects, on lineage diversification. We here combine assessments of historical biogeography, geomorphology, climatic niche, vegetative and floral trait evolution to test whether these factors jointly, or in isolation, explain diversification dynamics of a Neotropical plant clade (Merianieae, Melastomataceae). After estimating ancestral areas and the changes in niche and trait disparity over time, we employ Phylogenetic Path Analyses as a synthesis tool to test eleven hypotheses on the individual direct and indirect effects of these factors on diversification rates. We find strongest support for interlinked effects of colonization of the uplifting Andes during the mid-Miocene and rapid abiotic climatic niche evolution in explaining a burst in diversification rate in Merianieae. Within Andean habitats, later increases in floral disparity allowed for the exploitation of wider pollination niches (i.e., shifts from bee to vertebrate pollinators), but did not affect diversification rates. Our approach of including both vegetative and floral trait evolution, rare in assessments of plant diversification in general, highlights that the evolution of woody habit and larger flowers preceded the colonization of the Andes, but was likely critical in enabling the rapid radiation in montane environments. Overall, and in concert with the idea that ecological opportunity is a key element of evolutionary radiations, our results suggest that a combination of rapid niche evolution and trait shifts were critical for the exploitation of newly available niche space in the Andes in the mid-Miocene. Further, our results emphasize the importance of incorporating both abiotic and biotic factors into the same analytical framework if we aim to quantify the relative and interlinked effects of these processes on diversification.

The norpurpureine alkaloid from Annona purpurea inhibits human platelet activation in vitro

Background

The leaves of Annona purpurea have yielded several alkaloids with anti-aggregation activities against rabbit platelets. This is promising in the search for agents that might act against platelets and reduce the incidence of cardiovascular diseases. Since significant differences in platelet function have been reported between human and animal platelets, a study focusing on the effect of A. purpurea extracts against human platelet activation is necessary.

Methods

The compounds in an A. purpurea ethanolic extract underwent bio-guided fractionation and were used for in vitro human platelet aggregation assays to isolate the compounds with anti-platelet activity. The bioactive compounds were identified by spectroscopic analysis. Additional platelet studies were performed to characterize their action as inhibitors of human platelet activation.

Results

The benzylisoquinoline alkaloid norpurpureine was identified as the major anti-platelet compound. The IC₅₀ for norpurpureine was 80 μM against platelets when stimulated with adenosine 5′-diphosphate (ADP), collagen and thrombin. It was pharmacologically effective from 20 to 220 μM. Norpurpureine (220 μM) exhibited its in vitro effectiveness in samples from 30 healthy human donors who did not take any drugs during the 2 weeks prior to the collection. Norpurpureine also gradually inhibited granule secretion and adhesion of activated platelets to immobilized fibrinogen. At the intra-platelet level, norpurpureine prevented agonist-stimulated calcium mobilization and cAMP reduction. Structure–activity relationship analysis indicates that the lack of a methyl group at the nitrogen seems to be key in the ability of the compound to interact with its molecular target.

Conclusion

Norpurpureine displays a promising in vitro pharmacological profile as an inhibitor of human platelet activation. Its molecular target could be a common effector between Ca²⁺ and cAMP signaling, such as the PLC-PKC-Ca²⁺ pathway and PDEs. This needs further evaluation at the protein isoform level.

Electronic supplementary material

The online version of this article (10.1186/s11658-018-0082-4) contains supplementary material, which is available to authorized users.

Point Mutations at gyrA and gyrB Genes of Levofloxacin-Resistant Helicobacter pylori Isolates in the Esophageal Mucosa from a Venezuelan Population

The treatment of Helicobacter pylori infection is complicated by antibiotic resistance. A high levofloxacin (LVX) resistance rate was previously demonstrated in H. pylori isolates from gastric mucosa (40%) and esophagus (19%) in individual hosts of a Venezuelan population. We aimed to assess the molecular mechanisms of LVX resistance and susceptibility in isolates from the gastroesophageal mucosa, by studying point mutations in the quinolone resistance-determining region of gyrA and gyrB genes. Sequencing of gyrA and gyrB genes (N = 120) helped to identify point mutations in 60 isolates (30 from antrum and 30 from esophagus) of five dyspeptic patients. Double (Asn87Thr and Asp91Asn) and single (Asn87Ile or Asn87Thr) mutations in the gyrA gene were identified in the esophageal mucosa. These mutations have been commonly found in the stomach. Occurrence of a single (Asn87Ile) mutation was associated with high resistance (minimum inhibitory concentration ≥ 32 μg/mL) to LVX. Only a single (Ser479Gly) mutation was found in the gyrB gene in both mucosae. One patient presented isolates with no mutations in the two genes studied. Isolates with the same mutation pattern in individual hosts revealed identical genetic profiles for these genes, confirming that isolates identified in the esophageal mucosa come from isolates colonizing the stomach. Helicobacter pylori resistance to LVX in the esophagus is related to double- and single-point mutations in gyrA and gyrB genes, such as those found in the stomach. Levofloxacin should be applied with caution, because its antibiotic effect on H. pylori is decreasing in Latin America, perhaps owing to high prescription rates.

Multiple cag genotypes of Helicobacter pylori isolates colonize the oesophagus in individual hosts in a Venezuelan population

PURPOSE

Multiple Helicobacter pylori strains colonize and coexist in the stomach of one single patient, carrying heterogeneous distributions of cag genotypes. The oesophagus provides a niche for H. pylori colonization; however, little is known about its adaptive role.

METHODOLOGY

Using PCR for cagA, cagE and virB11 genes from cag-pathogenicity island (PAI) and Etest for antimicrobial susceptibility test, we determined cag-PAI genotypes associated with H. pylori virulence, when positive cultures were matching in both the stomach and the oesophagus (96 isolates; 8 out of 80 dyspeptic patients).

RESULTS

The stomach showed complete cag-PAI islands in 77 % of the isolates, whereas the oesophagus showed complete cag-PAI islands only in 44 % of the isolates. Expression of CagA and interleukin 8 correlated with inflammatory processes and histopathological changes in the stomach, but not in the oesophagus. Different cag-PAI profiles were found in both mucosae of an individual host, and at least one oesophagus profile corresponded to one profile identified in stomach. The antibiotic resistance profiles showed variability in the colonization by single or mixed H. pylori isolates in the gastric and oesophageal mucosa both intra- and inter-individuals.

CONCLUSION

These results demonstrate colonization with multiple H. pylori isolates in the oesophageal mucosa, like those found in the stomach of individual hosts. H. pylori was characterized by a dominant partial island, low interleukin 8 induction with lower histopathological damage and lower antibiotic resistance, suggesting that the microenvironmental changes in individual hosts select less virulent isolates in the oesophagus than in the stomach. New approaches to ensure effective eradication therapy in multi-resistant H. pylori strains must be developed.

Anti-inflammatory and antitumoural effects of Uncaria guianensis bark

ETHNOPHARMACOLOGICAL RELEVANCE

Uncaria guianensis (Aublet) Gmell (Rubiaceae) is a medicinal plant from the jungles of South and Central America, used to treat cancer, arthritis, diabetes, and inflammation. Evaluate the anti-inflammatory and anti-tumor effects of Uncaria guianensis preparations.

MATERIALS AND METHODS

Bio-guided fractionation of a hydroethanolic extract of Uncaria guianensis was performed, evaluating the fractions and subfractions for their effect on inflammatory mediators, tumour necrosis factor alpha (TNF-α), interleukin 6 (IL-6) and prostaglandin E2 (PGE2) by ELISA and nitric oxide (NO) by the Griess reaction in cultured supernatant from RAW 264.7 macrophages stimulated with lipopolysaccharide (LPS). The expression of cyclooxygenase 2 (COX-2), inducible nitric oxide synthase (iNOS) and inhibitor of κB (IκB) were investigated in RAW 264.7 macrophages by flow cytometry. The activity of NF-κB in HeLa cells transfected with a luciferase reporter system was determined. The effect of Uncaria guianensis on the inflammatory response in vivo was assessed in BALB/c mice stimulated with LPS, on rat paw oedema induced by carrageenan, and on tumour growth and lung metastasis in BALB/c mice inoculated with 4T1 mammary tumour cells. Immune cell infiltrates and inflammatory mediators were evaluated in the tumour by immunohistochemistry.

RESULTS

Sub-fraction Ug AIV inhibited, to varying degrees, NO, TNF-α, IL-6 and PGE2 production by macrophages in vitro (30 μg/ml) and in the serum of LPS-challenged mice (5 mg/kg). Macrophage expression of Cox-2 was inhibited (35%), IκB degradation was completely inhibited and NF-κB activation was inhibited (70%) by Ug AIV at 30 μg/ml. Ug AIV decreased paw oedema by 86% (5 mg/kg) and serum NO and TNF-α by 45% and 65% respectively. Ug AIV reduced 4T1 mammary tumour growth by 91% on day 33 post-inoculation as well as the levels of serum NO, IL-6 and TNF-α in the same animals. Ug AIV decreased the number of tumour-infiltrating T lymphocytes, macrophages and neutrophils as well as the number of cells positive for COX-2, iNOS, IL-6, TNF-α and p65.

CONCLUSIONS

As Ug AIV was not cytotoxic for tumour cells or macrophages, its anti-tumour effect may be due to a reduction in pro-tumoural inflammatory processes in the tumour microenvironment, possibly mediated through NF-κB.

Saikosaponin-d, a novel SERCA inhibitor, induces autophagic cell death in apoptosis-defective cells

Autophagy is an important cellular process that controls cells in a normal homeostatic state by recycling nutrients to maintain cellular energy levels for cell survival via the turnover of proteins and damaged organelles. However, persistent activation of autophagy can lead to excessive depletion of cellular organelles and essential proteins, leading to caspase-independent autophagic cell death. As such, inducing cell death through this autophagic mechanism could be an alternative approach to the treatment of cancers. Recently, we have identified a novel autophagic inducer, saikosaponin-d (Ssd), from a medicinal plant that induces autophagy in various types of cancer cells through the formation of autophagosomes as measured by GFP-LC3 puncta formation. By computational virtual docking analysis, biochemical assays and advanced live-cell imaging techniques, Ssd was shown to increase cytosolic calcium level via direct inhibition of sarcoplasmic/endoplasmic reticulum Ca(2+) ATPase pump, leading to autophagy induction through the activation of the Ca(2+)/calmodulin-dependent kinase kinase-AMP-activated protein kinase-mammalian target of rapamycin pathway. In addition, Ssd treatment causes the disruption of calcium homeostasis, which induces endoplasmic reticulum stress as well as the unfolded protein responses pathway. Ssd also proved to be a potent cytotoxic agent in apoptosis-defective or apoptosis-resistant mouse embryonic fibroblast cells, which either lack caspases 3, 7 or 8 or had the Bax-Bak double knockout. These results provide a detailed understanding of the mechanism of action of Ssd, as a novel autophagic inducer, which has the potential of being developed into an anti-cancer agent for targeting apoptosis-resistant cancer cells.

[Diagnosis of Helicobacter pylori infection by PCR in gastric juice and gastroesophageal biopsies from dyspeptic patients]

Helicobacter pylori is the main bacterial agent implicated in human gastroduodenal inflammatory pathologies; being one of the most common bacterial pathogens, with a high prevalence in Venezuela. The diagnosis of H. pylori infection is performed primarily in gastric biopsies through PCR; however, string-absorbed gastric juice and esophageal biopsies could be also used as alternative specimens to determine the infection. In this study the H. pylori infection was assessed in different specimens of the upper tract digestive of dyspeptic patients, though the detection by PCR of essential genes (glmM and ureA) and genes encoding virulence factors (cagA). Of 104 patients studied, H. pylori was found in 53.8, 69,2 and 58,7% of gastric juice, and gastric and esophageal biopsies, respectively; with predominance of the strains type I (cagA+) in juice and gastric biopsies, and strains type II (cagA-) in esophageal biopsies. The detection of H. pylori in gastric juice and esophageal biopsies showed high sensitivity and specificity, in comparison with the detection in gastric biopsies, suggesting that both types of specimens may be used efficiently for a secure diagnosis of H. pylori infection.

High frequency of Helicobacter pylori in the esophageal mucosa of dyspeptic patients and its possible association with histopathological alterations

BACKGROUND

Helicobacter pylori gastric colonization is known to be high in symptomatic subjects. However, only a few reports on the presence of H. pylori in the esophageal mucosa have been published. The aim of this study was to assess the frequency of H. pylori in the esophagus of dyspeptic patients and its association with histopathology.

METHODS

The presence of H. pylori in the gastroesophageal mucosa was detected by fluorescence in situ hybridization (FISH) and PCR analysis of DNA extracted from gastric and esophageal biopsies of 82 symptomatic patients, using genus- and species-specific PCR primers. Alterations in the gastroesophageal mucosa were assessed by conventional histological techniques.

RESULTS

H. pylori in the stomach was detected by PCR and FISH, respectively, in 61% (n=43) and 90% (n=63) of dyspeptic patients, and in the esophagus in 70% (n=44) and 73% (n=46). The prevalence of cagA-positive strains by PCR varied from 50% (n=35) in the gastric mucosa to 65% (n=41) in the esophageal mucosa. By combining the results of both methods, H. pylori was present in the gastroesophageal mucosa in 86% (n=68) of patients. The association of the presence of bacteria, including H. pylori, in the esophageal mucosa with histopathological alterations was statistically significant between microabscesses and bacteria (r=0.656, p<0.0001) and PCR detection and pseudogoblet cells (r=0.25, p<0.047).

CONCLUSIONS

This is the first report of the occurrence of H. pylori in the esophageal mucosa from dyspeptic Venezuelan patients. These results demonstrate the high prevalence of H. pylori in the esophagus, and its presence was correlated with signs of inflammation.

Inhibition of hepatitis B virus and human immunodeficiency virus (HIV-1) replication by Warscewiczia coccinea (Vahl) Kl. (Rubiaceae) ethanol extract

The primary objective of this study was to search for natural products capable of inhibiting hepatitis B virus (HBV) replication. The research design, methods and procedures included testing hydro-alcoholic extracts (n = 66) of 31 species from the Venezuelan Amazonian rain forest on the cell line HepG2 2.2.15, which constitutively produces HBV. The main outcomes and results were as follows: the species Euterpe precatoria, Jacaranda copaia, Jacaranda obtusifolia, Senna silvestris, Warscewiczia coccinea and Vochysia glaberrima exerted some degree of inhibition on HBV replication. The leaves of W. coccinea showed a significant antiviral activity: 80% inhibition with 100 µg mL⁻¹ of extract. This extract also exerted inhibition on covalently closed circular deoxyribonucleic acid (cccDNA) production and on HIV-1 replication in MT4 cells (more than 90% inhibition with 50 µg mL⁻¹ of extract). Initial fractionation using organic solvents of increasing polarity and water showed that the ethanol fraction was responsible for most of the antiviral inhibitory activities of both the viruses. It was concluded that Warscewiczia coccinea extract showed inhibition of HBV and HIV-1 replication. Bioassay-guided purification of this fraction may allow the isolation of an antiviral compound with inhibitory activity against both viruses.

High prevalence of dna from non-H. pylori helicobacters in the gastric mucosa of venezuelan pet dogs and its histological alterations

Non-H. pylori helicobacters (NHPH) have been demonstrated as gastric spiral-shaped bacteria in specimens obtained from dogs; however, their roles in the pathogenesis of upper gastrointestinal disease have not yet been clearly established. The purpose of this study was to evaluate the prevalence of NHPH DNA in the gastric mucosa of dogs and its association with histopathology. Helicobacter was detected through histopathological techniques, PCR, and FISH analysis from fundic biopsies of twenty dogs with or without signs of gastrointestinal disease. PCR and FISH were based on partial 16S rRNA gene sequences. Nineteen dogs showed mild to marked gastritis in the fundus, and only one dog had a healthy gastric mucosa. NHPH DNA was detected in 18 dogs with gastritis and one with normal gastric mucosa. However, there was no significant correlation between the presence of NHPH DNA and the degree of gastritis. These results show a high prevalence of NHPH DNA in the gastric mucosa of dogs from Venezuela. Further studies are necessary to determine a possible association between a specific NHPH species and the degree of gastritis.

Understanding the physiology of pre-fertilisation events in the human spermatozoa--a necessary prerequisite to developing rational therapy

Sperm dysfunction is the single most common defined cause of infertility. One in 15 men is sub-fertile and the condition is increasing in frequency. However, the diagnosis is poor and, excluding assisted conception, there is no treatment. The reason for this is our limited understanding of the biochemical, molecular and genetic functions of the spermatozoon. The underlying premise of our research programme is to establish a rudimentary understanding of the processes necessary for successful fertilisation. In this manuscript, we detail advances in our understanding of calcium signalling in the cell and outline genetic and proteomic technologies that are being used to improve the diagnosis of the condition.

Stomach lysozymes of the three-toed sloth (Bradypus variegatus), an arboreal folivore from the Neotropics

Lysozymes are antimicrobial defences that act as digestive enzymes when expressed in the stomach of herbivores with pre-gastric fermentation. We studied this enzyme in the complex stomach of the three-toed sloth (Bradypus variegatus), a folivore with pre-gastric fermentation. Lysozymes were identified by SDS-PAGE and immunoblotting in all portions: diverticulum, pouch, glandular and muscular prepyloric area with 14.3 kDa of molecular mass. Purified lysozymes from all areas but the diverticulum were characterized by MALDI-TOF, optimal pH, optimal ionic strength, and specific activity. The differences observed suggested at least three isoforms. The optimal pHs were similar to the pH of the stomach portion where the enzymes were isolated. The lysozyme from the pouch (fermentation chamber) exhibited higher specific activity and concentration than the others. The specific activity of the enzyme from the acid muscular prepyloric portion was comparable to that reported in the cow abomasums; however, its concentration was lower than that observed in cow. This distinctive pattern of secretion/specific activity and overall low concentration suggests different roles for the lysozymes in this herbivore compared to Artiodactyla. We postulate that sloth stomach lysozymes may still be antimicrobial defences by protecting the microbial flora of the fermentation chamber against foreign bacteria.

Calcium signalling in human spermatozoa: a specialized 'toolkit' of channels, transporters and stores

Ca(2+) is a ubiquitous intracellular messenger which encodes information by temporal and spatial patterns of concentration. In spermatozoa, several key functions, including acrosome reaction and motility, are regulated by cytoplasmic Ca(2+) concentration. Despite the very small size and apparent structural simplicity of spermatozoa, evidence is accumulating that they possess sophisticated mechanisms for regulation of cytoplasmic Ca(2+) concentration and generation of complex Ca(2+) signals. In this review, we consider the various components of the Ca(2+)-signalling 'toolkit' that have been characterized in somatic cells and summarize the evidence for their presence and activity in spermatozoa. In particular, data accumulated over the last few years show that spermatozoa possess one (and probably two) Ca(2+) stores as well as a range of plasma membrane pumps and channels. Selective regulation of the various components of the 'toolkit' by agonists probably allows spermatozoa to generate localized Ca(2+) signals despite their very small cytoplasmic volume, permitting the discrete and selective activation of cell functions.

Resistance of rumen bacteria murein to bovine gastric lysozyme

BACKGROUND

Lysozymes, enzymes mostly associated with defence against bacterial infections, are mureinolytic. Ruminants have evolved a gastric c type lysozyme as a digestive enzyme, and profit from digestion of foregut bacteria, after most dietary components, including protein, have been fermented in the rumen. In this work we characterized the biological activities of bovine gastric secretions against membranes, purified murein and bacteria.

RESULTS

Bovine gastric extract (BGE) was active against both G+ and G- bacteria, but the effect against Gram- bacteria was not due to the lysozyme, since purified BGL had only activity against Gram+ bacteria. We were unable to find small pore forming peptides in the BGE, and found that the inhibition of Gram negative bacteria by BGE was due to an artefact caused by acetate. We report for first time the activity of bovine gastric lysozyme (BG lysozyme) against pure bacterial cultures, and the specific resistance of some rumen Gram positive strains to BGL.

CONCLUSIONS

Some Gram+ rumen bacteria showed resistance to abomasum lysozyme. We discuss the implications of this finding in the light of possible practical applications of such a stable antimicrobial peptide.

An endogenous inhibitor of Ca++-ATPase from human placenta

Intracellular free calcium is regulated by Ca(++)-ATPase, one form present on the plasma membrane (PM Ca(++)-ATPase) and the other on sarcoplasmic (endoplasmic) reticulum (SR/ER Ca(++)-ATPase). An endogenous inhibitor of SR Ca(++)-ATPase from human placenta was shown to be present in normal placenta and the activity was not detectable in placenta from preeclamptic patients. The inhibitor was distributed in cytosol and microsomes. The inhibition of Ca(++)-ATPase by this inhibitor was concentration- and time-dependent. The inhibitor neither bound to DEAE- nor CM-sepharose resins at pH 7.5 and 8.5. Furthermore, it was heat stable for 15 min up to 55 degrees C and completely destroyed at 80 degrees C in a few minutes. It was also observed to be stable at room temperature for at least 3 months. The purification and characterization of this inhibitor would be valuable in achieving an understanding of the normal regulation of Ca(++)-ATPase in the placenta during pregnancy.

Requirement for vacuolar H+ -ATPase activity and Ca2+ gradient during entry of rotavirus into MA104 cells

The mechanism by which rotavirus and other nonenveloped viruses enter the cell is still not clear. We have proposed an endocytosis model where the critical step for virus uncoating and membrane permeabilization is the decrease in Ca(2+) concentration in the endosome. In this paper, we monitored rotavirus entry by measuring alpha-sarcin-rotavirus coentry and infectivity in MA104 cells. The participation of endocytosis, acidification, and endosomal Ca(2+) concentration on virus entry was studied by inhibiting the endosomal H(+)-ATPase with bafilomycin A1 and/or increasing the extracellular calcium reservoir by addition of 10 mM CaEGTA. Rotavirus-alpha-sarcin coentry was inhibited by bafilomycin A1 and by addition of 10 mM CaEGTA. These effects were additive. These substances induced a significant inhibition of infectivity without affecting virus binding and postentry steps. These results are compatible with the interpretation that bafilomycin A1 and CaEGTA block rotavirus penetration from the endosome into the cytoplasm and support our hypothesis of a Ca(2+)-dependent endocytosis model.

Are goats naturally resistant to gastric Helicobacter infection?

Gastric Helicobacter species are widespread and have been reported in wild and domestic mammals of different dietary habits such as humans, dogs, cats, macaques, mice, cheetahs, ferrets, swine and cattle. All have been associated with gastric pathologies. Recently, gastric Helicobacter species were shown to be widespread in cattle and swine in Europe, and there is a report of Helicobacter pylori in sheep in Italy. However, there are no reports of Helicobacter infection in the goat, another important domestic animal of human consumption. The aim of our study was to assess whether Helicobacter abomasal infection was common in goats slaughtered for human consumption. Infection was detected through PCR analysis of DNA extracted from gastric biopsies, using genus- and species-specific primers. Bovine and porcine gastric samples were also analyzed as positive controls. None of the 70 goats were positive for Helicobacter spp.; however, Candidatus Helicobacter bovis and Candidatus Helicobacter suis were detected in 85% of the bovine and 45% of the porcine samples, respectively. We discuss the possibility that goats may exhibit natural resistance to abomasal infection by Helicobacter spp.

Curcumin: a new cell-permeant inhibitor of the inositol 1,4,5-trisphosphate receptor

Curcumin (diferuoylmethane or 1,7-bis (4-hydroxy-3-methoxyphenol)-1,6-hepatadiene-3,5-dione) is the active ingredient of the spice turmeric. Curcumin has been shown to have a number of pharmacological and therapeutic uses. This study shows that curcumin is a potent inhibitor of the inositol 1,4,5-trisphosphate-sensitive Ca2+ channel (InsP3 receptor). In porcine cerebellar microsomes, the extent of InsP3-induced Ca2+ release (IICR) is almost completely inhibited by 50 microM curcumin (IC50 = 10 microM). As the extent of IICR cannot be restored back to control levels by the addition of excess InsP3 and since it has little effect on [3H]InsP3 binding to cerebellar microsomes, this inhibition is likely to be non-competitive in nature. IICR in cerebellar microsomes is biphasic consisting of a fast and slow component. The rate constants for the two components are both reduced by curcumin to similar extents (by about 70% of control values at 40 microM curcumin). In addition, curcumin also reduces agonist (ATP)-stimulated Ca2+ mobilization from intact HL-60 cells, indicating that curcumin is cell permeant. However, since it also affects intracellular Ca2+ pumps and possibly ryanodine receptors, it may lead to complex Ca2+ transient responses within cells, which may well explain some of its putative therapeutic properties.

Simultaneous measurement and imaging of intracellular Ca(2+) and H(+) transport in isolated rabbit gastric glands

1. Activation of H(+) secretion in the intracellular canaliculi of parietal cells occurs on an unknown time scale with ill-defined kinetics for the coupling of H(+) secretion and the elevation of intracellular calcium ([Ca(2+)](i)) stimulated by secretagogues. 2. We developed a method to determine H(+) secretion in isolated rabbit gastric glands with spatio-temporal resolution, using the fluorescent indicator Lysosensor Yellow-Blue (LYB). Glands accumulated the dye exclusively in the intracellular canaliculi of parietal cells and the gland lumen. Dye fluorescence in the acid spaces of the glands increased upon stimulation of acid secretion by carbachol, histamine and forskolin. Simultaneous fluorescence measurements of acid secretion and [Ca(2+)](i) at 1 s resolution were made by joint loading of LYB and Fluo-3. 3. Carbachol-stimulated H(+) secretion was detected in the gland lumen as early as 3 s after the onset of the [Ca(2+)](i) spike. H(+) accumulation appeared to be transient and paralleled the release component of the [Ca(2+)](i) spike. Short and repetitive stimulations with carbachol elicited repetitive responses in [Ca(2+)](i) and H(+) secretion. 4. Histamine or forskolin stimulated H(+) secretion with a delayed onset (around 2 min) and a sustained response. Acid secretion was temporally unrelated to the oscillatory Ca(2+) responses. 5. The striking difference in the kinetics of activation of H(+) secretion by cholinergic and cAMP-dependent secretagogues indicates that two distinct mechanisms are operating in the final stimulation of the pump, in spite of both eliciting a [Ca(2+)](i) response.

Inhibition of the SERCA Ca2+ pumps by curcumin. Curcumin putatively stabilizes the interaction between the nucleotide-binding and phosphorylation domains in the absence of ATP

Curcumin is a compound derived from the spice, tumeric. It is a potent inhibitor of the SERCA Ca2+ pumps (all isoforms), inhibiting Ca2+-dependent ATPase activity with IC50 values of between 7 and 15 microm. It also inhibits ATP-dependent Ca2+-uptake in a variety of microsomal membranes, although for cerebellar and platelet microsomes, a stimulation in Ca2+ uptake is observed at low curcumin concentrations (<10 microm). For the skeletal muscle isoform of the Ca2+ pump (SERCA1), the inhibition of curcumin is noncompetitive with respect to Ca2+, and competitive with respect to ATP at high curcumin concentrations ( approximately 10-25 microm). This was confirmed by ATP binding studies that showed inhibition in the presence of curcumin: ATP-dependent phosphorylation was also reduced. Experiments with fluorescein 5'-isothiocyanate (FITC)-labelled ATPase also suggest that curcumin stabilizes the E1 conformational state. The fact that FITC labels the nucleotide binding site of the ATPase (precluding ATP from binding), and the fact that curcumin affects FITC fluorescence indicate that curcumin must be binding to another site within the ATPase that induces a conformational change to prevent ATP from binding. This observation is interpreted, with the aid of recent structural information, as curcumin stabilizing the interaction between the nucleotide-binding and phosphorylation domains, precluding ATP binding.

Inositol 1,4,5-trisphosphate receptor isoforms show similar Ca2+ release kinetics

The inositol 1,4,5-trisphosphate receptor (InsP3R) is an intracellular Ca2+ release channel which upon activation initiates many cellular functions. Multiple InsP3R subtypes are expressed in most cell types but the physiological significance of this heterogeneity is poorly understood. This study has directly compared the functional properties of the three different InsP3R isoforms by analyzing their InsP3-induced Ca2+ release (IICR) properties in cell lines which predominantly express each isoform subtype. The InsP3-dependence of the amount or extent of IICR was InsP3R isoform-specific, with the type III isoform having the lowest affinity with respect to Ca2+ release. The transient kinetics of IICR, measured using stopped-flow spectrofluorimetry, however, were similar for all three InsP3R isoforms. At maximal InsP3 concentrations (20 microM) the rate constants where between 0.8 and 1.0 s(-1) for the fast phase and 0.25-0.45 s(-1) for the slow phase. The concentration of InsP3 required to induce half-maximal rates of Ca2+ release (EC50) were also similar for the three isoforms (0.2-0.4 microM for the fast phase and 0.75-0.95 microM for the slow phase). These results indicate the InsP3R channel does not significantly differ functionally in terms of Ca2+ release rates between isoforms. The temporal and spatial features of intracellular Ca2+ signals are thus probably achieved through InsP3R isoform-specific regulation or localization rather than their intrinsic Ca2+ efflux properties.

Inhibition of the type 1 inositol 1,4,5-trisphosphate-sensitive Ca2+ channel by calmodulin antagonists

This study describes the effects of a number of calmodulin antagonists on the cerebellar type 1 inositol 1,4,5-trisphosphate (InsP3) receptor. All the antagonists tested (trifluoperazine, fluphenazine, chlorpromazine and calmidazolium) inhibited the extent of InsP3-induced Ca2+ release (IICR) with similar IC(50) values (between 60 and 85 microM). They did not affect the efficacy of InsP3 to release Ca2+, since the concentrations of InsP3 required to cause half-maximal release was little affected in the presence of these agents. In addition, these agents did not affect InsP3 binding to its receptor. Stopped-flow studies to determine the rate constants of IICR showed this process to be biphasic with a fast and slow component. All the calmodulin antagonists appeared to reduce the rate constants for Ca2+ release in a phase-specific manner, preferentially reducing the fast phase component. Chlorpromazine (75 microM) appeared to have the most potent effect on the fast phase rate constant, reducing it from 1.0 to 0.08 s(-1), while only reducing the rate constant for the slow phase about twofold (0.2-0.08 s(-1)). The fact that calmodulin itself inhibits both IICR and InsP3 binding, while these calmodulin antagonists also reduce Ca2+ release and do not affect InsP3 binding, suggests that the mechanism of action of these agents is unlikely to be due to the reversal of the modulatory action of calmodulin on this receptor.

The effects of phenothiazines and other calmodulin antagonists on the sarcoplasmic and endoplasmic reticulum Ca(2+) pumps

The effects of a number of phenothiazines and other calmodulin antagonists on the Ca(2+)-ATPase activity of sarcoplasmic reticulum (SR) and endoplasmic reticulum (ER) were investigated. The drugs used in this study were trifluoperazine, calmidazolium, fluphenazine, chlorpromazine, W-7, and calmodulin-binding peptide. Our results showed that calmidazolium and calmodulin-binding peptide were the most potent inhibitors of skeletal muscle SR Ca(2+)-ATPase activity (isoform SERCA 1) (IC(50) values of 0.5 and 7 microM, respectively), while W-7 was the least potent inhibitor (IC(50), 125 microM). All of the antagonists had little effect on the cerebellar ER Ca(2+)-ATPase activity (isoform SERCA 2b), except for trifluoperazine, which had a biphasic effect, causing stimulation at low concentrations and inhibition at higher concentrations. Our results suggest that the effects of these calmodulin antagonists are independent of calmodulin and that they inhibit the Ca(2+)-ATPase in an isoform-specific manner. It was found that these antagonists inhibit the skeletal muscle isoform of the Ca(2+) pump by altering the Ca(2+) affinity and the associated Ca(2+)-binding steps, as well as possibly stabilising the E1 conformational state of the enzyme.

Subtype identification and functional properties of inositol 1,4, 5-trisphosphate receptors in heart and aorta

One of the major mechanisms by which hormones elevate intracellular Ca(2+)levels is by generating the second messenger inositol 1,4, 5-trisphosphate (InsP(3)), which activates a Ca(2+)channel (InsP(3)receptor) located in the endoplasmic reticulum (ER). This study undertakes to identify the InsP(3)receptor subtypes (isoforms) in heart and aorta and to characterize their functional properties. The InsP(3)receptor isoforms were identified from rat heart and aorta tissues using both reverse-transcriptase polymerase chain reaction (RT-PCR) to assess the presence of mRNA for the different isoforms and immunochemistry using InsP(3)receptor isoform-specific antibodies. Functional studies included ligand binding experiments using [(3)H]InsP(3)and InsP(3)-induced Ca(2+)release studies using Fluo-3 as the Ca(2+)sensing dye. All three isoforms of the InsP(3)receptor were identified using RT-PCR and immunochemical analyses. [(3)H]InsP(3)binding studies using microsomes derived from these tissues showed that heart had a 3-fold lower abundance of InsP(3)receptors than aorta, while both have considerably lower abundance than the well characterized cerebellar microsomes. The affinity of the InsP(3)binding to the receptor was also different in the three tissues. In cerebellum the K(d)was 60 nM, while aorta had a much higher K(d)of 220 nM. Heart microsomes, appeared to show two classes of binding affinity with K(d)s of 150 nM and 60 nM. Furthermore, the effects of free [Ca(2+)] on [(3)H]InsP(3)binding levels were also different for the three tissues. InsP(3)binding to both cerebellar and aorta microsomes decreased by 90% and 60%, respectively, above 30 nM free [Ca(2+)], while InsP(3)binding to heart was relatively insensitive to changes in [Ca(2+)]. At maximal InsP(3)concentrations, aorta microsomes were able to release about 5% of the accumulated Ca(2+), compared to 25% by cerebellar microsomes. Heart microsomes, however, showed only very little InsP(3)-induced Ca(2+)release ( <0.5%). The EC(50)concentration for InsP(3)-induced Ca(2+)release was 1.2 micro M for aorta while that for cerebellum was 0.3 micro M. Known agonists of the cerebellar InsP(3)receptor such as 3-deoxy InsP(3)and adenophostin A were also able to mobilize Ca(2+)from aorta microsomes. In addition, the competitive antagonist heparin and the non-competitive antagonists of the cerebellar InsP(3)receptor, tetracaine and tetrahexylammonium chloride, were also able to block InsP(3)-induced Ca(2+)release from aorta microsomes.

The mycotoxin paxilline inhibits the cerebellar inositol 1,4, 5-trisphosphate receptor

Paxilline, a tremorgenic alkaloid mycotoxin produced by Penicillium paxilline, is a reversible inhibitor of the cerebellar inositol 1,4, 5-trisphophate (InsP(3)) receptor. It inhibits the amount or extent of InsP(3)-induced Ca(2+) release (IICR), at sub-maximal concentrations of InsP(3), in a biphasic manner consistent with two inhibition constants (K(i)'s 6.7 and > or =400 microM). As paxilline does not affect InsP(3) binding to the receptor, it can be considered a non-competitive inhibitor. The fact that IICR is biphasic has been interpreted as there being two populations of InsP(3)-sensitive Ca(2+) stores, which release Ca(2+) in either a fast or slow fashion. This study has shown that the rate constants for Ca(2+) release from both the fast and slow populations are reduced by paxilline (100 microM) by about 70% and 60%, respectively. Detailed analysis of the way different concentrations of paxilline inhibit the rate constants for Ca(2+) release indicates that the population of Ca(2+) stores that contribute to the slower phase of Ca(2+) release is more sensitive to the inhibitory action of paxilline.

Estrogenic alkylphenols induce cell death by inhibiting testis endoplasmic reticulum Ca(2+) pumps

Industrial alkylphenols in the environment may act as "xenoestrogens" to disrupt testicular development and decrease male fertility. Amongst possible targets for these compounds are testicular Sertoli cells, which nurture the developing sperm cells. We demonstrate that SERCA 2 and 3 Ca(2+) pumps are relatively abundant in rat testis microsomal membranes, and also in Sertoli, myoid, and TM4 cells (a Sertoli cell line). A number of estrogenic alkylphenols such as nonylphenol, octylphenol, bisphenol A, and butylated hydroxytoluene all inhibit testicular Ca(2+) ATPase in the low micromolar concentration range. These agents also mobilize intracellular Ca(2+) in intact TM4 cells in a manner consistent with the inhibition of ER Ca(2+) pumps. Alkylphenols dramatically decrease the viability of TM4 cells, an effect that is reversed by either a caspase inhibitor or by BAPTA, and is therefore consistent with Ca(2+)-dependent cell death via apoptosis. We postulate that alkylphenols disrupt testicular development by inhibiting ER Ca(2+) pumps, thus disturbing testicular Ca(2+) homeostasis.

Role of Ca2+in the replication and pathogenesis of rotavirus and other viral infections

Ca2+ plays a key role in many pathological processes, including viral infections. Rotavirus, the major etiological agent of viral gastroenteritis in children and young animals, provides a useful model to study a number of Ca2+ dependent virus-cell interactions. Rotavirus entry, activation of transcription, morphogenesis, cell lysis, particle release, and the distant action of viral proteins are Ca2+ dependent processes. In the extracellular medium, Ca2+ stabilizes the structure of the viral capsid. During entry into the cell the low cytoplasmic Ca2+ concentration induced the solubilization of the outer protein layer of the capsid and transcriptase activation. Viral protein synthesis modifies Ca2+ homeostasis which, in turn, favours viral morphogenesis and induces cell death. The generation of diarrhea is a multifactorial process involving Ca2+ dependent secretory processes of mediators and water and electrolytes, as well as the induction of cell death in the different cell types that compose the intestinal epithelium. The discovery of the non-structural viral protein NSP4 as a viral enterotoxin and the possible participation of the enteric nervous system in the pathogenesis of diarrhea represent significant advances in its understanding. Ca2+ also plays a role in the replication cycles and pathogenesis of other viral diseases such as poliovirus, Coxsackie virus, cytomegalovirus, vaccinia and measles virus and HIV.

Critical evaluation of ECV304 as a human endothelial cell model defined by genetic analysis and functional responses: a comparison with the human bladder cancer derived epithelial cell line T24/83

Early reports indicated that ECV304 was a spontaneously-transformed line derived from a Japanese human umbilical vein endothelial cells (HUVEC) culture. Many morphological, immunochemical, and genetic studies provided further evidence that ECV304 was a valuable biomedical research tool and could be used to study processes that include angiogenesis in vitro and signal transduction by a variety of G protein-coupled receptors. However, several distinct differences between ECV304 and HUVEC are now apparent and recent reports have indicated genetic similarity between ECV304 and T24/83, a human bladder cancer cell line. To further assess the utility of ECV304 as a human endothelial cell model, we compared the functional responses of ECV304 and T24/83 to a range of G protein-coupled receptor agonists. We also used DNA fingerprinting to karyotype both ECV304 and T24/83. Both ATP and uridine triphosphate (UTP) stimulated inositol phosphate metabolism in ECV304 without alteration of cAMP levels. Comparative data using selective P2Y receptor agonists indicated that this response, leading to calcium mobilization from intracellular stores, was predominantly mediated by the activation of P2Y2 receptors. Similar responses were recorded from both ECV304 and T24/83 cells. ECV304 expressed a relatively high basal activity of NOS that was reduced by L-NAME and stimulated by P2Y2 receptor agonists. In contrast, P2Y2 receptor activation did not induce prostaglandin synthesis in ECV304. Both ECV304 and T24/83 express receptors for adenosine, adrenaline, and calcitonin, which stimulate adenylate cyclase. Proliferation of ECV304 and T24/83 cells, measured by the incorporation of [3H]thymidine into DNA, was largely serum-independent. This was in contrast to parallel experiments with porcine and bovine aortic endothelial cells that indicated a marked serum-dependent increase in DNA synthesis. Genetic analysis confirmed that ECV304 and T24/83 are identical. ECV304 displays some endothelial characteristics and is useful for the study of receptor pharmacology. However, ECV304 is not of HUVEC origin and is therefore an inappropriate cell line to study endothelial cell biology.

The mechanism of inhibition of the Ca2+-ATPase by mastoparan. Mastoparan abolishes cooperative ca2+ binding

The amphiphilic peptide mastoparan, isolated from wasp venom, is a potent inhibitor of the sarcoplasmic reticulum Ca2+-ATPase. At pH 7. 2, ATPase activity is inhibited with an inhibitory constant (Ki) of 1 +/- 0.13 microM. Mastoparan shifts the E2-E1 equilibrium toward E1 and may affect the regulatory ATP binding site. The peptide also decreases the affinity of the ATPase for Ca2+ and abolishes the cooperativity of Ca2+ binding. In the presence of mastoparan, the two Ca2+ ions bind independently of one another. Our results appear to support the model that describes the relationship between the two Ca2+ binding sites as "side-by-side," because this model allows the possibility of independent Ca2+ entry to the two sites. Mastoparan shifts the steady-state equilibrium between E1'Ca2 and E1'Ca2.P toward E1'Ca2.P, by possibly affecting the conformational change that follows ATP binding. The peptide also causes a reduction in the levels of phosphoenzyme formed from [32P]Pi. Some analogues of mastoparan were also tested and were found to cause inhibition of the Ca2+-ATPase in the range of 2-4 microM. The inhibitory action of mastoparan and its analogues appears dependent on their ability to form alpha-helices in membranes.

GroEL protects the sarcoplasmic reticulum Ca(++)-dependent ATPase from inactivation in vitro

The molecular chaperone, GroEL, facilitates correct protein folding and inhibits protein aggregation. The function of GroEL is often, though not invariably, dependent on the co-chaperone, GroES, and ATP. In this study it is shown that GroEL alone substantially reduces the inactivation of purified Ca(++)-ATPase from rabbit skeletal muscle sarcoplasmic reticulum. In the absence of GroEL, the enzyme became completely inactive in about 45-60 hours when kept at 25 degrees C, while in the presence of an equimolar amount of GroEL, the enzyme remained approximately 80% active even after 75 hours. Equimolar amounts of BSA or lysozyme were unable to protect the enzyme from inactivation under identical conditions. Analysis by SDS-PAGE showed GroEL was acting by blocking the aggregation of ATPase at 25 degrees C. GroEL was not as effective in protection at -20 degrees C or 4 degrees C. These results are discussed in the context of current models of the GroEL mechanism.

Expression and distribution of the type 1 and type 3 inositol 1,4, 5-trisphosphate receptor in developing vascular smooth muscle

The recent discoveries of inositol 1,4,5-trisphosphate (IP3) receptor subtypes with different affinities for IP3 and their potential involvement in development has important consequences for vascular smooth muscle. This study has examined the expression and distribution of the type 1 and type 3 IP3 receptor subtypes in developing rat vascular smooth muscles. Immunoblotting of portal vein and aorta from neonatal (2 to 4 days) and fully developed (6 weeks) rats revealed significantly higher levels of the type 3 IP3 receptor expression in neonatal, compared with developed, vascular smooth muscles. In contrast, expression of the type 1 IP3 receptor in neonates was lower compared with developed vascular smooth muscles. Immunolocalization of the type 3 IP3 receptors in neonatal tissues revealed that staining corresponded to the distribution of the sarcoplasmic reticulum (visualized by osmium ferricyanide staining of thin tissue sections), which suggested localization of the type 3 IP3 receptor throughout the sarcoplasmic reticulum network. We conclude that type 3 IP3 receptors are the predominant subtype in the development of vascular smooth muscle and are distributed throughout the sarcoplasmic reticulum in these cells. The switch in isoforms of the IP3 receptor during development from the type 3 with low affinity for IP3 to the higher-affinity type 1 receptor may play a role in calcium-mediated regulation of developing vascular smooth muscle.

Characterization of a membrane calcium pathway induced by rotavirus infection in cultured cells

Some viruses induce changes in membrane permeability during infection. We have shown previously that the porcine strain of rotavirus, OSU, induced an increase in the permeability to Na+, K+, and Ca2+ during replication in MA104 cells. In this work, we have characterized the divalent cation entry pathway by measuring intracellular Ca2+ in fura-2-loaded MA104 and HT29 cells in suspension. The permeability to Ca2+ and other cations was evaluated by the change of the intracellular concentration following an extracellular cation pulse. Rotavirus infection induced an increase in permeability to Ca2+, Ba2+, Sr2+, Mn2+, and Co2+. The rate of cation entry decreased over time as the intracellular concentration increased during the first 20 s. This indicates that regulatory mechanisms, including channel inactivation, are triggered. La3+ did not enter the cell and blocked the entry of the divalent cations in a dose-dependent manner. Metoxyverapamil (D600), a blocker of L-type voltage-gated channels, partially inhibited the entry of Ca2+ in virus-infected MA104 and HT29 cells. The results suggest that rotavirus infection of cultured cells activates a cation channel rather than nonspecific permeation through the plasma membrane. This activation involves the synthesis of viral proteins through mechanisms yet unknown. The increase in intracellular Ca2+ induced by the activation of this channel may be related to the increase in cytoplasmic and endoplasmic reticulum Ca2+ pools required for virus maturation and cell death.

Oncosis in MA104 cells is induced by rotavirus infection through an increase in intracellular Ca2+ concentration

Rotavirus infection modifies the metabolism and ionic homeostasis of the host cell. First, there is an induction of viral synthesis with a parallel shutoff of cell protein production, followed by an increase of plasma membrane Ca2+ permeability, thereby inducing an increase of free cytoplasmic and sequestered Ca2+ concentrations. Cell death follows at a later stage. We studied the role of the increase in Ca2+ concentration in cell death. An elevation of extracellular Ca2+ concentration during infection induced an increase in [Ca2+]i and potentiated cell death. Buffering the increases in [Ca2+]i with BAPTA added at 6 h p.i. reduced the cytopathic effect without inhibiting viral protein synthesis and infectious particle production. Metoxyverapamil (D600), a Ca2+ channel inhibitor, added at 1 h p.i. reduced Ca2+ permeability, the increases in [Ca2+]i, and cell death produced by infection without modifying viral protein synthesis and infectious titer. Thapsigargin, the inhibitor of Ca(2+)-ATPase of endoplasmic reticulum, potentiated the increase of [Ca2+]i and accelerated the time course of cell death. Double staining with fluorescein diacetate and ethidium bromide or acridine orange and ethidium bromide showed that infected MA104 cells had lost plasma membrane integrity without DNA fragmentation or formation of apoptotic bodies. These results support the hypothesis that the increase in [Ca2+]i due to a product of viral protein synthesis triggers the chain of events that leads to cell death by oncosis.

The role of inorganic phosphate in regulating the kinetics of inositol 1,4,5-trisphosphate-induced Ca2+ release: a putative role for endoplasmic reticulum phosphate transporters

The effects of phosphate and acylphosphonate phosphate transporter inhibitors were investigated on inositol 1,4,5-trisphosphate (InsP3)-induced Ca2+ release from cerebellar microsomes. Although neither changing the phosphate concentration nor adding phosphate transporter inhibitors affected the percentage (extent) of InsP3-induced Ca2+ release, they did, however, affect the transient kinetics of this process. InsP3-induced Ca2+ release is biphasic in nature, arising from two populations of InsP3-sensitive Ca2+ stores which either release Ca2+ in a fast or slow fashion. Altering phosphate concentration or adding phosphate transporter inhibitors appeared to affect only the fast phase component. We therefore suggest that these observations could be explained by the possibility that phosphate transporters only reside in the fast releasing InsP3-sensitive Ca2+ stores.

2-Hydroxycarbazole induces Ca2+ release from sarcoplasmic reticulum by activating the ryanodine receptor

2-Hydroxycarbazole was shown to induce Ca2+ release from skeletal muscle and cardiac muscle sarcoplasmic reticulum at concentrations between 100-500 microM. This release was blocked by both 1 mM tetracaine and 30 microM ruthenium red which inhibit the ryanodine receptor or by pre-treatment with 10 mM caffeine which depletes the ryanodine receptor-containing Ca2+ stores. This, in addition to the fact that 2-hydroxycarbazole has little effect on Ca2+ ATPase activity, indicates that it activates Ca2+ release through the ryanodine receptor. The apparent EC50 value for release from both skeletal muscle and cardiac muscle sarcoplasmic reticulum was approximately 200 microM and maximal release occurred at 400-500 microM, making it approximately 20 times more potent than caffeine. The dose-dependency in the extent of Ca2+ release induced by 2-hydroxycarbazole was also apparently highly cooperative for both preparations. That 2-hydroxycarbazole was able to mobilize Ca2+ from non-muscle cell microsomes and in intact TM4 cells (which contain ryanodine receptors), makes this compound a more potent and commercially available alternative to caffeine in studying the role of this intracellular Ca2+ channel in a variety of systems.

Biochemical mechanisms of calcium mobilisation induced by mastoparan and chimeric hormone-mastoparan constructs

Ca2+ efflux, Ca(2+)-ATPase, and membrane permeability measurements were used to investigate the biochemical mechanisms of Ca2+ release induced by mastoparan (MP) and the chimeric hormone-MP constructs incorporating galanin (galparan) or vasopressin antagonist (M375 and M391) moieties. Comparative studies utilised preparations of porcine cerebellar microsomes and rabbit skeletal muscle sarcoplasmic reticulum (SR). MP and chimeric peptides galparan, M375 and M391 induce Ca2+ release over a range of concentrations from 0.3-10 microM. Comparison of MP and three chimeric, N-terminal extended, constructs indicates that N-terminal extension modifies the biological properties of MP, producing changes in efficacy which are enzyme-isoform-specific. Biochemical studies indicate that the chimeric analogues and MP inhibit Ca(2+)-ATPases and directly activate the ryanodine receptor (RyR) to release Ca2+ from both heavy SR (HSR) and microsomes. The same peptides have no effect on the InsP3 receptor (InsP3R). Other actions that include modest changes in membrane permeability may also contribute to the Ca(2+)-mobilising action of MP and chimeric constructs.

Cell lines susceptible to infection are permeabilized by cleaved and solubilized outer layer proteins of rotavirus

It has previously been shown that trypsinized triple-layered particles of rotavirus induce destabilization of liposomes and membrane vesicles in the absence of Ca2+, a condition which leads to solubilization of the outer capsid proteins of the virus. In this work, we have studied the relationship between outer capsid solubilization and permeabilization of membrane vesicles, monitoring particle and vesicle size simultaneously by changes in light scattering. Permeabilization of intact cells induced by solubilized outer capsid proteins was monitored by following the rate of entry of ethidium bromide into the cells. Solubilized outer capsid proteins separated from double-layered particles induced vesicle permeabilization. Solubilization of the outer capsid preceded and was required for vesicle or cell permeabilization. Membrane damage induced by rotaviral outer proteins was not repaired upon addition of 1 mM Ca2+ to the medium. Rotavirus infection and cell permeabilization were correlated in six different cell lines tested. This phenomenon might be related to the mechanism of virus entry into the cell. We propose a new model for rotavirus internalization based on the permeabilizing ability of outer capsid proteins and the cycling of trapped calcium in the endosomal compartment.

Productive penetration of rotavirus in cultured cells induces coentry of the translation inhibitor alpha-sarcin

Internalization of rotavirus in MA104 cells was found to induce coentry of alpha-sarcin, a toxin that inhibits translation in cell-free systems and to which cells are normally impermeable. Entry of the toxin, measured by inhibition of protein synthesis at early times after infection, correlated with virus penetration leading to expression of infectivity, since toxin entry (1) was induced only by trypsin-treated triple-layered virions, to a degree dependent on the toxin and the virus concentration; (2) correlated with the degree of permissivity of different cell lines to rotavirus infection; (3) was inhibited to a similar extent as infectivity by treatment of cells with neuraminidase; and (4) was inhibited by pre- or postadsorption incubation of the virus with neutralizing monoclonal antibodies to VP7 and VP4 (VP8*). Neither the virus infectivity nor the toxin coentry was significantly affected by treatment of cells with bafilomycin A1, an inhibitor of the vacuolar proton ATPase, indicating that both events are independent of the endosomal acid pH. Virus-like particles (VLP), composed of rotavirus proteins 2/6/7/4, but not 2/6/7 or 2/6, were able to induce toxin entry as efficiently as virions. Use of genetically modified VLP in combination with the toxin coentry assay, which measures entry through a productive pathway, should allow identification of the regions of the outer capsid proteins essential for rotavirus penetration.

Effects of thimerosal on the transient kinetics of inositol 1,4,5-trisphosphate-induced Ca2+ release from cerebellar microsomes

Thimerosal, a thiol-reactive reagent, has been shown to increase the cytosolic Ca2+ concentration in a variety of cells by sensitizing inositol 1,4,5-trisphosphate (InsP3) receptors. Thimerosal can have both sensitizing (at concentrations of <2 microM) and inhibitory (at concentrations of >2 microM) effects on InsP3-induced Ca2+ release (IICR) from cerebellar microsomes. Transient kinetic studies were performed by employing a fluorimetric stopped-flow approach using fluo-3. IICR was found to be a bi-exponential process with a fast and a slow component. At a maximal InsP3 concentration (20 microM), the fast phase had a rate constant of 0.9 s-1 and the slow phase had a rate constant of 0.4 s-1. The amplitudes of the two phases were 60% and 40% respectively. When the rate constants for the two phases were plotted as Hill plots, the processes were found to be non-co-operative in both cases (Hill coefficient of 1.0), thus arguing for a simple mechanism linking InsP3 binding to channel opening. At a submaximal InsP3 concentration (0.2 microM), where the sensitizing effects of thimerosal are most pronounced, thimerosal increased the rate constants of both phases in a sigmoidal fashion, with a Hill coefficient of 4.0, suggesting that several cysteine residues (up to four) need to be modified in order for maximum sensitization to occur. The rate constants remained elevated even at thimerosal concentrations that inhibited IICR. The amplitude or extent of Ca2+ release was, however, elevated to a much greater extent in the slow phase, suggesting that the two phases respond differently. At maximal InsP3 concentrations, thimerosal has no effect upon the rate constants but inhibits the amplitude of Ca2+ release.