PubMed Health⌕ Search

Biomedical subjects

D S Friend

Publications and source records attributed to D S Friend.

At least 55 records · Page 3Linked to original sources
PubMed1993

Extravasation and transcytosis of liposomes in Kaposi's sarcoma-like dermal lesions of transgenic mice bearing the HIV tat gene.

Transgenic mice bearing the HIV tat gene develop dermal lesions resembling a common malignant tumor in AIDS, Kaposi's sarcoma (KS). To evaluate the permeability characteristics of these lesions and the therapeutic potential of drug-carrying liposomes, we have studied the localization of sterically stabilized liposomes, which show long circulation time in blood and increased accumulation in tumors. Liposomes encapsulating colloidal gold were injected intravenously into transgenic mice bearing KS lesions, and tissues were processed 24 hours later for both electron microscopy and for light microscopy with silver enhancement. Liposomes and silver marker were detected predominantly in the dermis surrounding the early and mature KS lesions, which were characterized by a proliferation of fibroblast-like spindle cells and abnormal blood vessels close to the epidermis. The silver-enhanced gold marker often surrounded vascular channels and scattered erythrocytes. As determined by electron microscopy, some spindle cells and macrophages had ingested intact liposomes. Transendothelial transport of liposomes was observed both through open channels between endothelial cells and also through endothelial cells lining intact vessels. Both extravasation and transcytosis of liposomes through irregular endothelium were much higher in KS lesions than in the adjacent normal skin. The high accumulation of sterically stabilized liposomes in KS lesions and their intracellular uptake by some spindle cells enhances their potential as carriers of chemotherapeutic agents against this neoplasm.

Animals↗
PubMed1992

Tumor necrosis factor-alpha and IFN-gamma expression in human thymus. Localization and overexpression in Down syndrome (trisomy 21).

In vitro studies suggest that TNF-alpha and IFN-gamma regulate thymocyte proliferation, but little evidence exists for the constitutive production of these cytokines in normal human thymus. In paired experiments, we examined frozen sections of postnatal human thymus from four control children and four age-matched children with Down syndrome (DS) (trisomy 21) for TNF-alpha and IFN-gamma mRNA expression using in situ hybridization. We studied thymuses from children with DS because this aneuploid condition is associated with a greatly increased incidence of infection and has abnormal thymic anatomy and patterns of thymocyte maturation. We found cells expressing constitutive levels of TNF-alpha mRNA in the trabeculae, corticomedullary junctions, and medulla of both control and DS thymuses and the number of these cells was an average of 3.9-fold higher in DS thymuses than in age-matched control thymuses. DS thymuses also contained an average of 3 fold higher numbers of cells with mast cell morphology, identified by toluidine blue histologic staining and electron microscopy. In both DS and control thymuses the mast cells colocalized with TNF-alpha mRNA-expressing cells. In addition, TNF-alpha protein- expressing cells, identified by immunohistochemistry, displayed a granular pattern of staining that is characteristic of mast cells. These results suggest that mast cells may be one source of TNF-alpha in human postnatal thymus. Discrete cells expressing IFN-gamma mRNA were distinctly localized to the cortical region of both DS and control thymuses and were 2.4-fold more abundant in DS thymuses than in the controls. Our results demonstrate, for the first time, the constitutive production and location of TNF-alpha and IFN-gamma in postnatal human thymus. The overexpression of both of these cytokines in DS thymuses suggests a dysregulation in cytokine production in DS and may provide an explanation for the abnormal thymic anatomy and thymocyte maturation associated with this syndrome.

Down Syndrome↗
PubMed1992

Microscopic localization of sterically stabilized liposomes in colon carcinoma-bearing mice.

Using light and electron microscopy, we investigated the in vivo distribution of liposomes sterically stabilized by specific lipids which prolong their circulation in blood. Tissue distribution of sterically stabilized liposomes composed of distearoyl phosphatidylcholine:cholesterol:monosialoganglioside GM1 (10:5:1)-encapsulated 67Ga-Desferal indicates that more than 30% of liposomes still remain in the blood at 24 h after tail vein injection. Moreover, such liposomes accumulated in tumors (C-26 colon carcinoma cells implanted s.c.), reaching almost the same level of uptake as liver (approximately 20% injected dose/g tissue). The microscopic localization of liposomes labeled with encapsulated colloidal gold or rhodamine-labeled dextran coincided well with the tissue distribution. To evaluate circulation parameters, two sizes of gold-containing egg phosphatidylcholine:cholesterol:distearoyl phosphatidylethanolamine (derivatized at its amino position with a 1900 molecular weight segment of polyethylene glycol) (10:5:0.8) liposomes were injected. The plasma was examined by electron microscopy of negative-stained preparations at 0.5, 4, and 24 h after liposome injection. It was found that the ratio of small (less than 100 nm diameter) to large (greater than 100 nm) liposomes increased with time, indicating a much faster clearance of the larger liposomes. To detect the localization of liposomes in various tissues, appropriate samples were fixed 24 h after the injection of gold-containing liposomes (between 80 and 100 nm in diameter) composed of egg phosphatidylcholine:cholesterol:monosialoganglioside GM1 (10:5:1) or egg phosphatidylcholine:cholesterol:derivatized distearoyl phosphatidylethanolamine. The tissues examined for this study included normal liver, bone marrow, and implanted neoplasms. Silver-enhanced colloidal gold was found predominantly within Kupffer cells in the normal liver and within macrophages in the bone marrow. Rarely were any silver-enhanced gold particles detected in hepatocytes. In all preparations, electron microscopy revealed the presence of gold in endosomes and lysosomes of fixed sinusoidal lining macrophages in the liver and bone marrow. Peripheral to the implanted tumors, silver enhancement revealed gold in small blood vessels and focally beyond the vessel boundaries in extracellular spaces around tumor cells. Gold particles were not observed within the tumor cell cytoplasm. At the tumor border, nonenhanced gold was occasionally seen by electron microscopy in cells of the mononuclear phagocyte system. We obtained the same localization pattern as with silver enhancement by using an alternative aqueous content marker, rhodamine B isothiocyanate-dextran. We conclude that liposomes of specific composition, which have the ability to remain in circulation with a half-life of 12-24 h, are also able to transverse the endothelium of small blood vessels, including those in tumors, and extravasate into extracellular spaces.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Translation and granule localization of mouse mast cell protease-5. Immunodetection with specific antipeptide Ig.

An antibody to mouse mast cell protease-5 (MMCP-5) was obtained by immunizing a rabbit with a 17-residue synthetic peptide corresponding to the unique amino acid sequence at residues 146 to 162 in this serine protease. After affinity purification, anti-MMCP-5(146-162) Ig reacted in SDS-PAGE immunoblots to recombinant MMCP-5 and to the native MMCP-5 protein present in the lysates of mouse serosal mast cells and the MC5 line of Kirsten sarcoma virus-immortalized mouse mast cells. Immunocytochemical staining localized MMCP-5 to the cytoplasmic granules of serosal mast cells and Kirsten sarcoma virus-immortalized mouse mast cells. Because mouse bone marrow-derived mast cells express abundant amounts of MMCP-5 mRNA, anti-MMCP-5(146-162) Ig was used to study the translation and granule accumulation of this protease when progenitor cells differentiate into these immature mouse mast cells. Maximal expression of MMCP-5 mRNA occurred after bone marrow cells had been cultured for 2 wk in IL-3-rich WEHI-3 cell conditioned medium, and MMCP-5 protein was detected in these cells. However, electron-microscopic analysis with gold-labeled antibody revealed that the amount of MMCP-5 in the individual granules of bone marrow-derived mast cells varied. The highest concentration of MMCP-5 was found in the most electron-dense secretory granules of the cells. These studies demonstrate the ultrastructural localization of the earliest transcribed mouse mast cell chymase, MMCP-5, and its granule accumulation during the differentiation of mouse bone marrow progenitor cells into immature mouse mast cells.

Amino Acid Sequence↗
PubMed1992

Schistosoma mansoni: cell-specific expression and secretion of a serine protease during development of cercariae.

Eukaryotic serine proteases are an important family of enzymes whose functions include fertilization, tissue degradation by neutrophils, and host invasion by parasites. To avoid damaging the cells or organisms that produced them, serine proteases must be tightly regulated and sequestered. This study elucidates how the parasitic blood fluke Schistosoma mansoni synthesizes, stores, and releases a serine protease during differentiation of its invasive larvae. In situ hybridization with a cDNA probe localized the protease mRNA to acetabular cells, the first morphologically distinguishable parasite cells that differentiate from the embryonic cell masses present in the intermediate host snail. The acetabular cells contained vimentin but not cytokeratins, consistent with a mesenchymal, not epithelial, origin. Antiprotease antibodies, localized by immunoperoxidase, showed that the protease progressively accumulated in these cells and was packaged in vesicles of three morphologic types. Extension of cytoplasmic processes containing protease vesicles formed "ducts" which reached the anterior end of fully differentiated larvae. During invasion of human skin, groups of intact vesicles were released through the acetabular cytoplasmic processes and ruptured within the host tissue. Ruptured protease vesicles were noted adjacent to degraded epidermal cells and dermal-epidermal basement membrane, as well as along the surface of the penetrating larvae themselves. These observations are consistent with the proposed dual role for the enzyme in facilitating invasion of host skin by larvae and helping to release the larval surface glycocalyx during metamorphosis to the next stage of the parasite.

Animals↗
PubMed1992

Fusion activity and inactivation of influenza virus: kinetics of low pH-induced fusion with cultured cells.

The kinetics of fusion of influenza virus (A/PR/8/34) with human promyelocytic leukaemia (HL-60), human T lymphocytic leukaemia (CEM) and murine lymphoma (S49) cells were investigated. Fusion was demonstrated by electron microscopy, and monitored by fluorescence dequenching of octadecylrhodamine incorporated in the virus membrane. Rapid fusion was induced upon mild acidification of the medium. At pH 5, all virus particles were capable of fusing with the cells. The initial rate and the extent of fusion were maximal between pH 4.9 and 5.2 and declined sharply below and above this range. The rate constants of adhesion of influenza virus to cells or erythrocyte ghosts were large, indicating a diffusion-controlled process. The rate constants of fusion of the virus with cells were smaller than those found previously for fusion with various liposomes. Although preincubation of the virus at acidic pH in the absence of target membranes almost completely inactivated the virus in its ability to fuse with erythrocyte ghosts, it reduced the extent of fusion with cultured cells by only 20 to 40%. Kinetic analysis of fusion revealed a mode of inactivation of the virus bound to erythrocyte ghosts or suspension cells, below pH 5.4, different from that of the virus preincubated at low pH without target membranes.

Cell Membrane↗
PubMed1992

Efficacies of liposome-encapsulated streptomycin and ciprofloxacin against Mycobacterium avium-M. intracellulare complex infections in human peripheral blood monocyte/macrophages.

Current treatments of disseminated infection caused by the Mycobacterium avium-M. intracellulare complex (MAC) are generally ineffective. Liposome-mediated delivery of antibiotics to MAC-infected tissues in vivo can enhance the efficacy of the drugs (N. Düzgüneş, V. K. Perumal, L. Kesavalu, J. A. Goldstein, R. J. Debs, and P. R. J. Gangadharam, Antimicrob. Agents Chemother. 32:1404-1411, 1988; N. Düzgüneş, D. A. Ashtekar, D. L. Flasher, N. Ghori, R. J. Debs, D. S. Friend, and P. R. J. Gangadharam, J. Infect. Dis. 164:143-151, 1991). We investigated the therapeutic efficacies of liposome-encapsulated streptomycin and ciprofloxacin against growth of the MAC inside human peripheral blood monocyte/macrophages. Treatment was initiated 24 h after infection of macrophages with the MAC and stopped after 20 h, and the cells were incubated for another 7 days. The antimycobacterial activity of streptomycin was enhanced when the drug was delivered to macrophages in liposome-encapsulated form, reducing the CFU about threefold more than the free drug did throughout the concentration range studied (10 to 50 micrograms/ml). With 50 micrograms of encapsulated streptomycin per ml, the CFU were reduced to 11% of the initial level of infection. Liposome-encapsulated ciprofloxacin was at least 50 times more effective against the intracellular bacteria than was the free drug: at a concentration of 0.1 microgram/ml, liposome-encapsulated ciprofloxacin had greater antimycobacterial activity than the free drug at 5 microgram/ml. With liposome-encapsulated ciprofloxacin at 5 micrograms/ml, the CFU were reduced by more than 1,000-fold at the end of the 7-day incubation period, compared with untreated controls. These results suggest that liposome-encapsulated ciprofloxacin or other fluoroquinolones may be effective against MAC infections in vivo.

Ciprofloxacin↗
PubMed1992

Prolonged transgene expression in rodent lung cells.

We tested the efficiency of several different cationic liposome formulations, complexed to one of two different chloramphenicol acetyltransferase (CAT) reporter plasmids, in transfecting freshly isolated, highly purified rat lung alveolar type II cells, alveolar macrophages, and three different human lung carcinoma cell lines, as well as NIH 3T3 cells, a rapidly dividing, transformed mouse fibroblast line. Our results demonstrated that several different cationic liposome formulations can mediate high-level CAT gene expression in all the cell types tested. Electron microscopic analysis confirmed that cationic liposome-DNA complexes are avidly bound and internalized by lung cells. The time course of expression of transfected genes in nontransformed cell types with low mitotic indices, such as type II cells, is poorly characterized. NIH 3T3 cells expressed maximal CAT activity by day 4 following transfection, with virtual disappearance of activity by day 11. Conversely, type II cells expressed maximal CAT activity between days 5 and 11, and CAT activity was still clearly present 35 days after transfection. Southern blot analysis of DNA isolated from transfected type II cells revealed that the CAT gene was largely present in an extrachromosomal form, rather than integrated into genomic DNA. These observations indicate that following cationic liposome-mediated transfection, rat alveolar type II cells (the majority of which do not divide in culture) can express transfected genes for prolonged periods, apparently mediated by expression of the transgene in an episomal form.

3T3 Cells↗
PubMed1991

Light microscopic localization of silver-enhanced liposome-entrapped colloidal gold in mouse tissues.

Silver-enhanced liposome-entrapped colloidal gold was developed for light microscopic localization of liposomes. Preparation of colloidal gold entrapped in liposomes was achieved by a modified method of Hong, et al. (1983) Biochim. Biophys. Acta 732, 320-323). In this report, a gold chloride/citrate solution of low pH (3.4) was used to inhibit the formation of gold granules during the liposome preparation. The diameter of most liposomes ranged from 80 to 100 nm. Following liposome preparation, the pH was adjusted to 6, and the temperature increased to 55 degrees C. The majority of the liposomes contained one to three gold particles. Liposomes were injected into mice via tail vein; 24 h later, tissues were collected. Sections were processed for silver enhancement of the gold particles and examined by light microscopy. Silver-enhanced gold particles were clearly observed in both liver and implanted tumor. Localization was confirmed by electron and fluorescence microscopy. Thus, we have shown that silver enhancement of colloidal gold liposomes is a direct and sensitive method for tracing the fate of liposomes in vivo, providing minimal background interference and a good definition of various cell types.

Animals↗
PubMed1991

A mechanism for differential release of acrosomal enzymes during the acrosome reaction.

To study the organization of fertilization enzymes in the sperm acrosome, we isolated and characterized two physicochemically distinct acrosomal fractions of guinea-pig spermatozoa. A soluble fraction contained the 25,000-Mr acrosomal autoantigen, AA1, and most of the acrosomal hyaluronidase and dipeptidyl peptidase II activity. A particulate fraction, designated acrosomal matrix (AM), consisted of membraneless crescent-shaped structures, and contained most of the acrosomal proacrosin. The AM also contained a 28,000-Mr putative proacrosin-binding protein, and a very-high-Mr component which, on reduction, was dissociated into 48,000-Mr and 67,000-Mr subunits. Autoproteolytic dissolution of the AM correlated with proteolysis by acrosin of the 28,000-Mr and 48,000-Mr AM molecules. Components of both the AM and the soluble fraction were localized by immuno-electron microscopy to the electron-dense region of the guinea-pig sperm acrosome. We conclude that acrosomal molecules are segregated into soluble and matrix compartments. This segregation is a function of disulphide bonding and non-covalent interactions among the relatively few components of the AM. Association of acrosin with the AM may be the mechanism by which this enzyme's release from the spermatozoon during the acrosome reaction is delayed relative to the release of other acrosomal molecules.

Acrosin↗
PubMed1991

Chloride ion transport in transformed normal and cystic fibrosis epithelial cells.

The inability of beta-adrenergic agonists (eg. isoproterenol) to activate a specific apical membrane chloride channel in epithelial cells is characteristic of cystic fibrosis (CF). The study of these channels has been facilitated by the transformation of human airway epithelial cells. Clonal populations of SV40 large T-antigen transformed airway epithelial cells from both normal and cystic fibrosis individuals have been established. A limitation in the use of these cell lines has been the loss of the ability to form tight junctions after multiple subcultures. In particular, this loss appears to be associated with cell "crisis". A selection protocol that involves growing cells in medium that is high in Ca2+ and supplemented with fetal bovine serum (FBS) has been employed to facilitate progression through crisis. One cell line (1HAEo-) that has a normal phenotype and retains tight junctions post-crisis has been produced using this protocol. Immunofluorescent staining with a monoclonal antibody to the E-cadherin adhesion molecule shows a characteristic pericellular localization, indicating the presence of the junctional complex. The presence of tight junctions has been confirmed by electron microscopy. These cells produce elevated (greater than 30 fold) levels of cAMP in response to exposure to isoproterenol or forskolin. Chloride ion transport, as measured by 36Cl- efflux, is stimulated greater than 2 fold by these agents. Three post-crisis CF cell lines which grow in serum-containing medium have been established. These do not exhibit tight junctions. Elevated (greater than 25 fold) levels of cAMP are detected in these cells after addition of isoproterenol or forskolin, but this increase in cAMP is not accompanied by an increase in 36Cl-efflux. Both normal (1HAEo-) and CF cells show increased 36Cl-efflux following addition of the calcium ionophore A23187. (ABSTRACT TRUNCATED AT 250 WORDS)

Biological Transport, Active↗
PubMed1991

Treatment of Mycobacterium avium-intracellulare complex infection in beige mice with free and liposome-encapsulated streptomycin: role of liposome type and duration of treatment.

Current treatments for Mycobacterium avium-intracellulare complex (MAC) infections are generally ineffective. Thus, the potential of free or liposome-encapsulated streptomycin to treat acute MAC infection was investigated in beige mice. Free streptomycin administered intramuscularly 5 days a week (150 mg/kg) was effective in the liver, spleen, and lungs. At 4 weeks, liposome-encapsulated streptomycin, administered intravenously in weekly doses (15 mg/kg), reduced the colony-forming units in the liver and spleen by about the same extent as a 50- to 100-fold higher dose of free drug. With 4 weekly injections of liposomes, the colony-forming units in the liver and spleen were lower by 2.4 and 2.9 log units, respectively, compared to untreated controls, even by the end of 12 weeks. The effects of unilamellar and multilamellar liposomes were similar. These observations suggest that liposome encapsulation not only targets streptomycin to infected cells but also increases the residual activity of the drug.

Animals↗
PubMed1990

Morphology of mammalian sperm membranes during differentiation, maturation, and capacitation.

The mammalian spermatozoon is a highly polarized cell whose surface membrane can be divided into five functionally, structurally, and biochemically distinct domains. These domains are formed during spermatogenesis, continue to be modified during passage through the epididymis, and are further refined in the female reproductive tract. The integrity of these domains appears to be necessary for the sperm to perform its function--fusion with the egg and subsequent fertilization. The domains can be identified morphologically by their surface contours and texture, the content, distribution, and organization of intramembranous particles after freeze-fracture, and by the density of surface and cytoplasmic electron-dense coatings in thin sections. By using a variety of labels that stain carbohydrates (lectins), lipids (filipin and polymyxin B), and monoclonal antibodies to specific membrane constituents, the biochemical composition of these contiguous membrane regions has also been partly elucidated. We review here what is known about the structure, composition, and behavior of each membrane domain in the mature sperm and include some information regarding domain formation during spermatogenesis. The sperm is an excellent model system to study the creation and maintenance of cell polarity, granule exocytosis, and fertilization. Hopefully this review will provide impetus for future studies aimed more directly at addressing the relationship of its morphology to its functions.

Acrosome↗
PubMed1989

Fusion of liposomes containing a novel cationic lipid, N-[2,3-(dioleyloxy)propyl]-N,N,N-trimethylammonium: induction by multivalent anions and asymmetric fusion with acidic phospholipid vesicles.

The fusion behavior of large unilamellar liposomes composed of N-[2,3-(dioleyloxy)propyl]-N,N,N-trimethylammonium (DOTMA) and either phosphatidylcholine (PC) or phosphatidylethanolamine (PE) has been investigated by a fluorescence resonance energy transfer assay for lipid mixing, dynamic light scattering, and electron microscopy. Polyvalent anions induced the fusion of DOTMA/PE (1:1) liposomes with the following sequence of effectiveness: citrate greater than EDTA greater than phosphate, in the presence 100 mM NaCl, pH 7.4. Sulfate, dipicolinate, and acetate were ineffective. DOTMA/PC (1:1) vesicles were completely refractory to fusion in the presence of multivalent anions in the concentration range studied, consistent with the inhibitory effect of PC in divalent cation induced fusion of negatively charged vesicles. DOTMA/PE vesicles could fuse with DOTMA/PC vesicles in the presence of high concentrations of citrate, but not of phosphate. Mixing of DOTMA/PE liposomes with negatively charged phosphatidylserine (PS)/PE or PS/PC (1:1) vesicles resulted in membrane fusion in the absence of multivalent anions. DOTMA/PC liposomes also fused with PS/PE liposomes and, to a limited extent, with PS/PC liposomes. These observations suggest that the interaction of the negatively charged PS polar group with the positively charged trimethylammonium of DOTMA is sufficient to mediate fusion between the two membranes containing these lipids and that the nature of the zwitterionic phospholipid component of these vesicles is an additional determinant of membrane fusion.

Animals↗
PubMed1989

Red cell deformability and lipid composition in two forms of acanthocytosis: enrichment of acanthocytic populations by density gradient centrifugation.

Whole cell deformability and lipid determinations were performed on red cells from two patients who had acanthocytes in the peripheral blood (10% and 20% to 30%) and normal serum lipoprotein levels. One patient had typical chorea-acanthocytosis and the other had no clinical abnormalities associated with acanthocytosis. Red cells from the patient with chorea-acanthocytosis showed reduced deformability, as measured by a visco-diffractometric method (ektacytometry), which could be explained by the presence of increased numbers of dehydrated cells containing high concentrations of hemoglobin. The total cell population showed a modest increase in potassium efflux, which may be responsible for reduced cation content and dehydration in a subpopulation of cells. When the patients' red cells were separated into different density populations by centrifugation on density gradients, the cells of classic acanthocyte morphology were concentrated in the high-density layers. This was true for both patients, although the subject with acanthocytes and no clinical disorder had a normal red cell density distribution. Lipid analysis of both types of acanthocytes showed an increase in the relative proportion of sphingomyelin with respect to the glycerophospholipids. Total cholesterol and phospholipid levels were reduced in the chorea-acanthocytosis red cells, but the other acanthocytes did not differ significantly in total lipid content from normal control samples. Thus, the one common abnormal feature in these two forms of acanthocytosis is the increase in the proportion of red cell sphingomyelin. Because this is a very stable, immobile component of the membrane, we suggest that its relative enrichment could result from a defect in the transport and maintenance of glycerophospholipids. Further study of the dynamics of glycerophospholipid organization in acanthocytes may be useful in increasing our understanding of the genesis of abnormal, acanthocytic morphology.

Acanthocytes↗
PubMed1987

Primary cultures of the dog's tracheal epithelium: fine structure, fluid, and electrolyte transport.

Cells from the dog's tracheal mucosa formed confluent epithelial sheets in culture. Typical tight junctions separated the apical from the basolateral portion of the cell membrane. The apical portion of the cell contained numerous short microvilli and a pronounced glycocalyx. The basolateral portion of the plasma membrane was unspecialized except for extensive gap junctions between cells. Freeze-fracture showed that the cultured cells lacked the basolateral square (orthogonal) arrays of the original tissue, particles previously implicated in ion transport. Formation of domes indicated the presence of active fluid absorption. Domes appeared between days 4 and 8 of culture and persisted for about 1 week. Cell sheets showed a transepithelial resistance of approximately equal to 400 omega X cm2 and a short-circuit current (Isc) of approximately 5 microA X cm-2. The effects of transport inhibitors indicated that both active Na absorption and active Cl secretion were present. Isc was increased by isoproterenol, prostaglandins E2 and F2 alpha, vasoactive intestinal peptide, dibutyryl cyclic AMP, leukotrienes C4 and D4, and bradykinin. These changes were probably due to stimulation of active Cl secretion.

Animals↗
PubMed1987

Influence of the membrane undercoat on filipin perturbation of the red blood cell membrane.

Filipin, a polyene antibiotic, interacts with beta-hydroxy sterols such as cholesterol in most cell membranes, forming bumps and pits that are visible by electron microscopy of freeze-fracture replicas. The markedly reduced perturbability of the red blood cell (RBC) membrane, compared to other cells, has been attributed to the constraining influence of the red cell membrane skeleton, the undercoat composed of spectrin, actin, and protein 4.1. To test the influence of the membrane skeleton on filipin-induced perturbation of the RBC membrane, we studied the interaction of filipin with red cells that were inherently devoid of spectrin and RBC in which spectrin had been crosslinked or denatured. These spectrin-deficient, crosslinked, and denatured cells have a fivefold increase in the number of filipin-induced perturbations as compared to control cells, despite equivalent membrane cholesterol content. These findings confirm that the spectrin-based membrane skeleton strongly influences the organization of the membrane so as to limit perturbation by filipin:cholesterol interaction and that for membranes in which the cholesterol content is known, filipin is a useful probe for testing the avidity of spectrin-based cytoskeletal attachment.

Animals↗