Humic acid induces oxidative DNA damage,growth retardation,and apoptosis in human primary fibroblasts

Humic acid (HA) has been implicated as an etiological factor of Blackfoot disease endemic in the southwest coast of Taiwan. Dysfunction of endothelial cells and vasculopathy have been proposed to explain the onset of ulcerous changes at extremities. However, little is known about the effect of HA on activities of cells in these nonhealing wounds. In the present study, we demonstrate that HA adversely affects the growth properties of fibroblasts, one of the key players in wound repair. HA treatment caused growth arrest and apoptosis in human foreskin fibroblasts (HFF). This was accompanied by a significant increase in the level of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in cellular DNA. The increased fluorescence in dichlorofluorescin (H2DCF)-stained and HA-treated cells suggests the involvement of reactive oxygen species (ROS) in HA-induced biological effects. Conversely, vitamin E pretreatment, which significantly reduced the 8-OHdG formation in HA-treated cells, alleviated the growth-inhibitory and apoptosis-inducing effects of HA. These results indicate that HA initiates oxidative damages to fibroblasts, and leads to their dwindling growth potential and survival. The present study suggests that HA-induced growth retardation and apoptosis of fibroblasts may play a role in the pathogenesis of Blackfoot disease.     

Norwalk virus-like particle hemagglutination by binding to h histo-blood group antigens

Noroviruses are a major cause of epidemic acute nonbacterial gastroenteritis worldwide. Here we report our discovery that recombinant Norwalk virus virus-like particles (rNV VLPs) agglutinate red blood cells (RBCs). Since histo-blood group antigens are expressed on gut mucosa as well as RBCs, we used rNV VLP hemagglutination (HA) as a model system for studying NV attachment to cells in order to help identify a potential NV receptor(s). rNV VLP HA is dependent on low temperature (4 degrees C) and acidic pH. Of the 13 species of RBCs tested, rNV VLPs hemagglutinated only chimpanzee and human RBCs. The rNV VLPs hemagglutinated all human type O (11 of 11), A (9 of 9), and AB (4 of 4) RBCs; however, few human type B RBC samples (4 of 14) were hemagglutinated. HA with periodate- and neuraminidase-treated RBCs indicated that rNV VLP binding was carbohydrate dependent and did not require sialic acid. The rNV VLPs did not hemagglutinate Bombay RBCs (zero of seven) that lack H type 2 antigen, and an anti-H type 2 antibody inhibited rNV VLP HA of human type O RBCs. These data indicated that the H type 2 antigen functions as the rNV VLP HA receptor on human type O RBCs. The rNV VLP HA was also inhibited by rNV VLP-specific monoclonal antibody 8812, an antibody that inhibits VLP binding to Caco-2 cells. Convalescent-phase sera from NV-infected individuals showed increased rNV VLP HA inhibition titers compared to prechallenge sera. In carbohydrate binding assays, the rNV VLPs bound to synthetic Lewis d (Le(d)), Le(b), H type 2, and Le(y) antigens, and these antigens also inhibited rNV VLP HA of human type O RBCs. Overall, our results indicate that carbohydrate antigens in the gut are a previously unrecognized factor in NV pathogenesis.     

Promoting neoplastic transformation of humic acid in mouse epidermal JB6 Cl41 cells

Humic acid (HA), a group of high-molecular weight polymer, resulting from the decomposition of organic matter has been implicated as a possible etiological factor for Blackfoot disease and cancer. In this study, we evaluate the promotion effect of HA on the transformation in mouse epidermal JB6 clone 41 (JB6 Cl41) cells that have been used to identify the tumor promoting activity of various compounds. Our preliminary assay demonstrated that JB6 Cl41 cells with the treatment of HA at the concentration of 100 microg/ml for 72 and 96 h significantly increased reactive oxygen species (ROS) as compared to the untreated control. In addition, the 48 h cultured cells with HA pretreatment for 48 h also increased ROS as compared to the untreated control. HA-pretreated cells develop highly scattered and spindle-shaped cells with few observable cell-cell contacts, and contain more filopodia. In vitro wound-healing assay showed that JB6 Cl41 cells with HA pretreatment increased the migrating growth. Furthermore, transformed foci of JB6 Cl41 cells following the HA pretreatment were observed after 6 weeks culture. In anchorage-independent growth assay, we found that HA promoted the colony formation and that colonies were inhibited by antioxidant N-acetyl cysteine (NAC). Our results suggest that HA may promote the transformation of epidermal cells and that this process is mediated by the generation of ROS.     

Trace element concentration and arsenic speciation in the well water of a Taiwan area with endemic Blackfoot disease

Blackfoot disease is a peripheral vascular disease resulting in gangrene of the lower extremities. Although extensive epidemiological study has implicated high arsenic content in artesian well water in the endemic area, there is more to learn about the etiology of the disease. In this study, effort is paid on multielement determination and arsenic speciation in order to find out whether the trace element concentration pattern in well water in the Blackfoot disease endemic area is different from those of two control areas. Experimental results indicate that the concentrations of Fe, P, Na, and Ba in well water in the Blackfoot disease endemic area are found to be significantly higher than those of the controls, but they are still below the drinking water standard. The total arsenic in well water in the endemic area (671±149 ppb) is much higher than that of one normal control area of Hsin-Chu (<0.7 ppb), but is a similar level as that of other control areas of I-Lan (653±71 ppb) where no Blackfoot disease has ever been found. It was also found that the insoluble arsenic in the endemic area (21.9 ppb) is much higher than that in two control areas (≤1.8 ppb), and the concentration ratio between As(III) and As(V) species in the endemic area (2.6) is much lower than that in one of the control areas, where the total arsenic is also high (14.7). The possible connection of Blackfoot disease with trace elements, arsenic species, and possibly other as yet undefined environmental factors in the artesian well water, is discussed.     

Arsenic concentration in the urine of patients with Blackfoot disease and Bowen’s disease

Extensive epidemiological study implicates that high arsenic content in artesian well water is the causal factor responsible for Blackfoot disease. We determine the arsenic concentration in urine samples of patients with Blackfoot and Bowen’s diseases and examine whether there exists any discrepancy of urinary arsenic concentrations among patients and the normal population. The analyses were made by hydride atomic absorption spectrophotometry (AAS) and the analytical reliability of the method was checked with a standard urine sample (ORTHO Bi-Level Urine Metal Control). The results show that the mean urinary arsenic concentration in 100 healthy adults is 63.4±29.7 μg/L, and those means for 23 and 11 patients with Blackfoot disease and Bowen’s disease are 75.7±39.1 μg/L (P vs controls >0.05) and 201±58 μg/L (P vs controls <0.001), respectively. From the analytical results obtained, we cannot conclude that urinary arsenic is associated with Blackfoot disease, as was disclosed from the epidemiological studies. However, urinary arsenic concentrations are possibly very closely associated with Bowen’s disease.     

Trace elements in hair of blackfoot disease

Blackfoot disease is a peripheral vascular disease resulting in gangrene of the lower extremities. Though extensive epidemiological study has implicated that high arsenic content in artesian well water of the endemic area, bears some important connection with the disease, the etiology of the disease is still unknown. In this study, attention is paid to multielement determination in order to find out whether the trace elements in hair of Blackfoot disease patients are different from those of the controls. Experimental results indicate that the concentrations of As and Se in hair of patients are significantly higher than those of the controls, but Ca and Zn are significantly lower than those of the controls. The possible connection of these elements with the etiology of the disease is discussed.     

Long-range effects on the binding of the influenza HA to receptors are mediated by changes in the stability of a metastable HA conformation

X-ray studies show that influenza hemagglutinin (HA) forms an elongated structure connecting the influenza virus at one end to cell-surface receptors at the other. At neutral pH, the 20 N-terminal residues of HA2—referred to as the fusion peptide—are buried in a hydrophobic pocket, about 100 Å away from the receptor-binding site, and thus seem unlikely to affect HA binding to the receptor. To test this assumption, we mutated residues in the fusion peptide, heterologically expressed the mutated proteins in COS7 cells, and examined their ability to bind fluorescently labeled red blood cells (RBCs). Surprisingly, a significantly reduced binding was recorded for some of the mutants. Ample experimental data indicate that HA has at least two forms: the native structure at neutral pH (N) that is metastable and the fusogenic form (F), observed at low pH, which is stable. Thus, a simple interpretation of our data is that HA can bind to its receptors at the RBC surface in the N form much more effectively than in the F (or in any other stable) form and that the altered binding properties are due to destabilizing effects of the mutations on the N form. That is, some of the mutations involve reduction in the free energy barrier between the N and F forms. This, in turn, leads to reduction in the population of the N form, which is the only form capable of binding to the cell-surface receptors. To explore this possibility, we estimated the stability free energy difference between HA wild-type (wt) and mutants in the N form using an empirical surface tension coefficient. The calculated stability differences correlated well with the measured binding, supporting the above interpretation. Our results are examined taking into account the available experimental data on the affinity of different soluble and membrane-attached forms of HA to its receptors.     

Chemical speciation of arsenic in urine of patients with blackfoot disease

Blackfoot disease is a peripheral vascular disease resulting in gangrene of the lower extremities. Although extensive epidemiological study has implicated high arsenic content in artesian well water of the endemic area bears some important connection with the disease, the etiology of the disease is still not clarified. In this study, attention is paid to chemical speciation of arsenic in order to find out whether the concentrations of arsenic species in urine of Blackfoot disease patients are different from those of controls. Experimental results indicate that the total arsenic, inorganic arsenic, monomethylarsonic acid, and other forms of arsenic in the urine of patients are significantly higher than those of the contols. The possible connection of those arsenic species with the etiology of the disease is discussed.     

Arsenic,selenium, and zinc in patients with blackfoot disease

Blackfoot disease is a peripheral vascular disease resulting in gangrene of the lower extremities. Extensive epidemiological study implicates that high arsenic content in artesian well water is the responsible causal factor of the disease. In the present study the concentrations of arsenic, selenium, and zinc in the body fluids and hair of patients with Blackfoot disease, in comparison to age- and sex-matched normal controls, are investigated. Two analytical techniques that include atomic absorption spectrometry and neutron activation analysis were used for the analysis of urine, serum, hair, and whole blood. The analytical results indicate that hair arsenic of the patients is significantly higher than that of the controls, but still below the critical value of 1 μg/g. In addition, the patients showed significantly lower concentrations of Se and Zn in the urine and blood than the normal controls. The possible connection of these elements with the etiology of the disease is discussed.     

Inner but Not Outer Membrane Leaflets Control the Transition from Glycosylphosphatidylinositol-anchored Influenza Hemagglutinin-induced Hemifusion to Full Fusion

Cells that express wild-type influenza hemagglutinin (HA) fully fuse to RBCs, while cells that express the HA-ectodomain anchored to membranes by glycosylphosphatidylinositol, rather than by a transmembrane domain, only hemifuse to RBCs. Amphipaths were inserted into inner and outer membrane leaflets to determine the contribution of each leaflet in the transition from hemifusion to fusion. When inserted into outer leaflets, amphipaths did not promote the transition, independent of whether the agent induces monolayers to bend outward (conferring positive spontaneous monolayer curvature) or inward (negative curvature). In contrast, when incorporated into inner leaflets, positive curvature agents led to full fusion. This suggests that fusion is completed when a lipidic fusion pore with net positive curvature is formed by the inner leaflets that compose a hemifusion diaphragm. Suboptimal fusion conditions were established for RBCs bound to cells expressing wild-type HA so that lipid but not aqueous dye spread was observed. While this is the same pattern of dye spread as in stable hemifusion, for this “stunted” fusion, lower concentrations of amphipaths in inner leaflets were required to promote transfer of aqueous dyes. Also, these amphipaths induced larger pores for stunted fusion than they generated within a stable hemifusion diaphragm. Therefore, spontaneous curvature of inner leaflets can affect formation and enlargement of fusion pores induced by HA. We propose that after the HA-ectodomain induces hemifusion, the transmembrane domain causes pore formation by conferring positive spontaneous curvature to leaflets of the hemifusion diaphragm.     

Protective role of Spirulina feed in a freshwater fish (Poecilia reticulata Peters) exposed to an azo dye-methyl red

Acute toxicity of an azo dye-methyl red (5-40 ppm) was examined under starving conditions, on two groups of Poecilia reticulata--a freshwater fish, fed on different diets prior to their exposure to dye. Besides natural feed, fish of group-1 also received Spirulina feed for one month (feed population), whereas those of group-2 received only natural feed (non-feed population). The mortality data revealed non-feed population to be more tolerant to feed stress during acute toxicity study, whereas feed population exhibited better tolerance to the combined stress of both feed and methyl red; especially at higher concentrations of the latter. RBCs in methyl red treatments acquired different shapes (poikilocytosis) and an increase in their size (anisocytosis) was also noticed. Percentage of such abnormal RBCs was almost equal in both feed and non-feed populations, except at a lower concentration (5 ppm), at which percentage of poikilocytic RBCs was lesser in the feed population. RBC counts in the control non-feed fish (34.5 x 10(4)/mm3) were significantly lower than control feed population (50.0 x 10(4) /mm3). Their number decreased with an increase in methyl red concentrations in non-feed population (9-26%), but percent reduction in RBC counts was almost similar (20-26%) at various concentrations of methyl red (5-30 ppm) in the feed population. Despite reduction in RBC counts, feed population did not suffer from anemia in methyl red treatments, as evident by their RBC counts which were almost equal to control fish of non-feed population. The results suggest that Spirulina feed improves tolerance of test organism towards methyl red manifested by noticeable reduction in the cytotoxic effects on RBCs and a lower mortality rate at higher concentrations of dye.     

RanBP1 stabilizes the interaction of Ran with p97 nuclear protein import

In this study we tested the hypothesis that fusion mediated by the influenza virus hemagglutinin (HA) is a cooperative event. To so this we characterized 3T3 cell lines that express HA at nine different defined surface densities. HA densities ranged from 1.0 to 12.6 x 10(3) HA trimers/microns2 as determined by quantitative fluorescent antibody binding. The lateral mobility and percent mobile fraction of HA did not vary significantly among these cells, nor did the contact area between HA-expressing cells and target RBCs. The fusion reaction of each HA- expressing cell line was analyzed using a fluorescence dequenching assay that uses octadecylrhodamine (R18)-labeled RBCs. For each cell line we measured the lag time preceding the onset of fusion, the initial rate of fusion, and final extent of fusion. The final extent of fusion was similar for all cell lines, and the initial rate of fusion as a function of HA surface density displayed a Michaelis-Menten-type dependence. However, the dependence of the lag time preceding the onset of fusion on HA surface density was clearly sigmoidal. Kinetic analysis of the data for the reciprocal lag time vs HA surface density, by both a log/log plot and a Hill plot, suggested that the observed sigmoidicity does not reflect cooperativity at the level of formation of HA aggregates as a prerequisite to fusion. Rather, the cooperativity of the process(es) that occur(s) during the lag time arises at a later step and involves a minimum of three, and most likely four, HA trimers. A model is proposed to explain HA cooperativity during fusion.     

Fusion Activity of Transmembrane and Cytoplasmic Domain Chimeras of the Influenza Virus Glycoprotein Hemagglutinin

The role of the sequence of transmembrane and cytoplasmic/intraviral domains of influenza virus hemagglutinin (HA, subtype H7) for HA-mediated membrane fusion was explored. To analyze the influence of the two domains on the fusogenic properties of HA, we designed HA-chimeras in which the cytoplasmic tail and/or transmembrane domain of HA was replaced with the corresponding domains of the fusogenic glycoprotein F of Sendai virus. These chimeras, as well as constructs of HA in which the cytoplasmic tail was replaced by peptides of human neurofibromin type1 (NF1) or c-Raf-1, NF78 (residues 1441 to 1518), and Raf81 (residues 51 to 131), respectively, were expressed in CV-1 cells by using the vaccinia virus-T7 polymerase transient-expression system. Wild-type and chimeric HA were cleaved properly into two subunits and expressed as trimers. Membrane fusion between CV-1 cells and bound human erythrocytes (RBCs) mediated by parental or chimeric HA proteins was studied by a lipid-mixing assay with the lipid-like fluorophore octadecyl rhodamine B chloride (R18). No profound differences in either extent or kinetics could be observed. After the pH was lowered, the above proteins also induced a flow of the aqueous fluorophore calcein from preloaded RBCs into the cytoplasm of the protein-expressing CV-1 cells, indicating that membrane fusion involves both leaflets of the lipid bilayers and leads to formation of an aqueous fusion pore. We conclude that neither HA-specific sequences in the transmembrane and cytoplasmic domains nor their length is crucial for HA-induced membrane fusion activity.     

Effects of sphingolipids overload on red blood cell properties in Gaucher disease

Gaucher disease (GD) is a genetic disease with mutations in the GBA gene that encodes glucocerebrosidase causing complications such as anaemia and bone disease. GD is characterized by accumulation of the sphingolipids (SL) glucosylceramide (GL1), glucosylsphingosine (Lyso‐GL1), sphingosine (Sph) and sphingosine‐1‐phosphate (S1P). These SL are increased in the plasma of GD patients and the associated complications have been attributed to the accumulation of lipids in macrophages. Our recent findings indicated that red blood cells (RBCs) and erythroid progenitors may play an important role in GD pathophysiology. RBCs abnormalities and dyserythropoiesis have been observed in GD patients. Moreover, we showed higher SL levels in the plasma and in RBCs from untreated GD patients compared with controls. In this study, we quantified SL in 16 untreated GD patients and 15 patients treated with enzyme replacement therapy. Our results showed that the treatment significantly decreases SL levels in the plasma and RBCs. The increased SL content in RBCs correlates with abnormal RBC properties and with markers of disease activity. Because RBCs lack glucocerebrosidase activity, we investigated how lipid overload could occur in these cells. Our results suggested that SL overload in RBCs occurs both during erythropoiesis and during its circulation in the plasma.     

Antiproliferative effect of topic hyaluronic acid gel. Study in gingival biopsies of patients with periodontal disease

Hyaluronic acid (HA) is the most abundant glycosaminoglycan of high molecular weight in the extracellular matrix of soft periodontal tissues. Our group recently demonstrated an HA-induced reduction in lymphoplasmocyte inflammatory infiltrate in periodontal disease. The objective of this study was to determine the effect of an HA gel of high molecular weight on cell proliferation, inflammation, and different periodontal lesion parameters. A double-blind clinical trial was conducted on the effect of an HA gel on cell proliferation in gingival biopsies from 28 patients with periodontal disease. A split-mouth design was used, randomly applying the gel to one quadrant and a placebo to the contralateral one. A gingival biopsy was taken for histopathological and immunohistochemical study, in order to determine the expression of cell proliferation antigen Ki-67 and to evaluate the inflammatory infiltrate. HA gel treatment induced a significant reduction in the proliferation index of the gingival epithelium, with 276 (range 234-317) Ki-67-positive cells per mm2 in treated samples versus 514 (range 158-876) per mm2 in controls (Mann-Whitney U test, p<0.003). In 13 patients, the number of Ki-67-positive fibroblastic cells was reduced by the treatment, whereas in 6 patients no differences were found (global difference, p=0.12). In 10 patients, Ki-67-positive cells were decreased in chronic inflammatory infiltrate present in the lamina propria, whereas in 6 patients no differences were found (global difference, p=0.054). We conclude that high molecular-weight HA gel reduces cell proliferation in epithelial cells such as fibroblasts and lymphocytes, abates the inflammatory process, and improves the periodontal lesion in patients with chronic periodontitis.     

Stimulation of human red blood cells leads to Ca2+-mediated intercellular adhesion

Red blood cells (RBCs) are a major component of blood clots, which form physiologically as a response to injury or pathologically in thrombosis. The active participation of RBCs in thrombus solidification has been previously proposed but not yet experimentally proven. Holographic optical tweezers and single-cell force spectroscopy were used to study potential cell-cell adhesion between RBCs. Irreversible intercellular adhesion of RBCs could be induced by stimulation with lysophosphatidic acid (LPA), a compound known to be released by activated platelets. We identified Ca²⁺ as an essential player in the signaling cascade by directly inducing Ca²⁺ influx using A23187. Elevation of the internal Ca²⁺ concentration leads to an intercellular adhesion of RBCs similar to that induced by LPA stimulation. Using single-cell force spectroscopy, the adhesion of the RBCs was identified to be approximately 100 pN, a value large enough to be of significance inside a blood clot or in pathological situations like the vasco-occlusive crisis in sickle cell disease patients.     

Using stable isotope analysis to obtain dietary profiles from old hair: a case study from Plains Indians

Stable isotope composition of human tissue reflects that of foods consumed, and can provide information about diet independent of artifactual remains. Here we refine and test this method by analyzing nitrogen (delta(15)N) and carbon (delta(13)C) isotope ratios in historic North American Plains Indians hair. Gas-source isotope-ratio mass spectrometry provides high-precision data for both delta(15)N and delta(13)C (+/-0.2 per thousand, 1 sigma) in single hair strands as short as 2 cm (100-150 mug). Because hair contains more carbon than nitrogen, if only delta(13)C data are needed, shorter strands (<1 cm) can be analyzed. This reduction in sample size opens new opportunities for analysis of small hair fragments found in archaeological excavations, as well as for analysis of seasonal variations in long hair strands. We find distinct isotope profiles (delta(15)N vs. delta(13)C) for two cultural groups, the Lower Brule reservation Sioux of 1892 and the reservation Blackfoot of 1892 and 1935. The resultant dietary profiles indicate a higher consumption of meat by the Blackfoot and a higher consumption of maize (or of animals that had fed on maize or other C(4) plants) by the Lower Brule. The two groups of Blackfoot yield similar isotopic profiles despite the passage of four decades, suggesting a strong role for cultural preference even as food sources change. Such stable isotope profiles can be used to link samples from the same cultural tradition based on their similar diets.     

The Lian Site,an Historic Log Shelter in Yellowstone County,Montana

Abstract

Thomas and Alice Kehoe have recently reported on an example of a Blackfoot clay vessel (Kehoe 1961), Their specimen is most interesting due to the fact that it is sun-dried and exemplifies a very late carry-over of the Blackfoot pottery tradition, The Kehoes postulate that this and similar-type specimens were used as specialized containers for the burning of sweet pine before medicine bundles. In support of this contention, and as a probable archaeological example of this practice, the author reports on the occurrence in central Montana of a similartype vessel which was found in a burnedout log shelter of possible Blackfoot construction, The find is analyzed in the light of Blackfoot-Crow relations during the 18th and 19th centuries.     

Ligation of Glycophorin A Generates Reactive Oxygen Species Leading to Decreased Red Blood Cell Function

Acute, inflammatory conditions associated with dysregulated complement activation are characterized by significant increases in blood concentration of reactive oxygen species (ROS) and ATP. The mechanisms by which these molecules arise are not fully understood. In this study, using luminometric- and fluorescence-based methods, we show that ligation of glycophorin A (GPA) on human red blood cells (RBCs) results in a 2.1-fold, NADPH-oxidase-dependent increase in intracellular ROS that, in turn, trigger multiple downstream cascades leading to caspase-3 activation, ATP release, and increased band 3 phosphorylation. Functionally, using 2D microchannels to assess membrane deformability, GPS-ligated RBCs travel 33% slower than control RBCs, and lipid mobility was hindered by 10% using fluorescence recovery after photobleaching (FRAP). These outcomes were preventable by pretreating RBCs with cell-permeable ROS scavenger glutathione monoethyl ester (GSH-ME). Our results obtained in vitro using anti-GPA antibodies were validated using complement-altered RBCs isolated from control and septic patients. Our results suggest that during inflammatory conditions, circulating RBCs significantly contribute to capillary flow dysfunctions, and constitute an important but overlooked source of intravascular ROS and ATP, both critical mediators responsible for endothelial cell activation, microcirculation impairment, platelet activation, as well as long-term dysregulated adaptive and innate immune responses.     

GPI-anchored influenza hemagglutinin induces hemifusion to both red blood cell and planar bilayer membranes

Under fusogenic conditions, fluorescent dye redistributed from the outer monolayer leaflet of red blood cells (RBCs) to cells expressing glycophosphatidylinositol-anchored influenza virus hemagglutinin (GPI- HA) without transfer of aqueous dye. This suggests that hemifusion, but not full fusion, occurred (Kemble, G. W., T. Danieli, and J. M. White. 1994. Cell. 76:383-391). We extended the evidence for hemifusion by labeling the inner monolayer leaflets of RBCs with FM4-64 and observing that these inner leaflets did not become continuous with GPI-HA- expressing cells. The region of hemifusion-separated aqueous contents, the hemifusion diaphragm, appeared to be extended and was long-lived. But when RBCs hemifused to GPI-HA-expressing cells were osmotically swollen, some diaphragms were disrupted, and spread of both inner leaflet and aqueous dyes was observed. This was characteristic of full fusion: inner leaflet and aqueous probes spread to cells expressing wild-type HA (wt-HA). By simultaneous video fluorescence microscopy and time-resolved electrical admittance measurements, we rigorously demonstrated that GPI-HA-expressing cells hemifuse to planar bilayer membranes: lipid continuity was established without formation of fusion pores. The hemifusion area became large. In contrast, for cells expressing wt-HA, before lipid dye spread, fusion pores were always observed, establishing that full fusion occurred. We present an elastic coupling model in which the ectodomain of wt-HA induces hemifusion and the transmembrane domain, absent in the GPI-HA-expressing cells, mediates full fusion.