Chloride Transport in Biological Membranes

Synthetic ion transporters can induce apoptosis by facilitating chloride anion transport into cells
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Historical Collection. You do not have JavaScript enabled. Please enable JavaScript to access the full features of the site or access our non-JavaScript page. Issue 18, Previous Article Next Article. From the journal: Chemical Communications. Molecular ferries: membrane carriers that promote phospholipid flip-flop and chloride transport. Bradley D. Lambert a.

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You have access to this article. Please wait while we load your content Something went wrong. Try again? Unlike diffusion of a substance from where it is more concentrated to less concentrated, filtration uses a hydrostatic pressure gradient that pushes the fluid—and the solutes within it—from a higher pressure area to a lower pressure area. Filtration is an extremely important process in the body.

Chloride Transport in Biological Membranes

For example, the circulatory system uses filtration to move plasma and substances across the endothelial lining of capillaries and into surrounding tissues, supplying cells with the nutrients. Filtration pressure in the kidneys provides the mechanism to remove wastes from the bloodstream. For all of the transport methods described above, the cell expends no energy. Membrane proteins that aid in the passive transport of substances do so without the use of ATP. During active transport, ATP is required to move a substance across a membrane, often with the help of protein carriers, and usually against its concentration gradient.

One of the most common types of active transport involves proteins that serve as pumps. Similarly, energy from ATP is required for these membrane proteins to transport substances—molecules or ions—across the membrane, usually against their concentration gradients from an area of low concentration to an area of high concentration.

These pumps are particularly abundant in nerve cells, which are constantly pumping out sodium ions and pulling in potassium ions to maintain an electrical gradient across their cell membranes. An electrical gradient is a difference in electrical charge across a space. In the case of nerve cells, for example, the electrical gradient exists between the inside and outside of the cell, with the inside being negatively-charged at around mV relative to the outside. This process is so important for nerve cells that it accounts for the majority of their ATP usage.

Active transport pumps can also work together with other active or passive transport systems to move substances across the membrane. For example, the sodium-potassium pump maintains a high concentration of sodium ions outside of the cell. Therefore, if the cell needs sodium ions, all it has to do is open a passive sodium channel, as the concentration gradient of the sodium ions will drive them to diffuse into the cell. In this way, the action of an active transport pump the sodium-potassium pump powers the passive transport of sodium ions by creating a concentration gradient.

When active transport powers the transport of another substance in this way, it is called secondary active transport. Symporters are secondary active transporters that move two substances in the same direction. Because cells store glucose for energy, glucose is typically at a higher concentration inside of the cell than outside. However, due to the action of the sodium-potassium pump, sodium ions will easily diffuse into the cell when the symporter is opened. The flood of sodium ions through the symporter provides the energy that allows glucose to move through the symporter and into the cell, against its concentration gradient.

Conversely, antiporters are secondary active transport systems that transport substances in opposite directions. Other forms of active transport do not involve membrane carriers. Once pinched off, the portion of membrane and its contents becomes an independent, intracellular vesicle. A vesicle is a membranous sac—a spherical and hollow organelle bounded by a lipid bilayer membrane. Endocytosis often brings materials into the cell that must to be broken down or digested.

Many immune cells engage in phagocytosis of invading pathogens. Like little Pac-men, their job is to patrol body tissues for unwanted matter, such as invading bacterial cells, phagocytize them, and digest them. Phagocytosis and pinocytosis take in large portions of extracellular material, and they are typically not highly selective in the substances they bring in. Cells regulate the endocytosis of specific substances via receptor-mediated endocytosis.

Receptor-mediated endocytosis is endocytosis by a portion of the cell membrane that contains many receptors that are specific for a certain substance.

Iron, a required component of hemoglobin, is endocytosed by red blood cells in this way. Iron is bound to a protein called transferrin in the blood. Specific transferrin receptors on red blood cell surfaces bind the iron-transferrin molecules, and the cell endocytoses the receptor-ligand complexes. Many cells manufacture substances that must be secreted, like a factory manufacturing a product for export.

These substances are typically packaged into membrane-bound vesicles within the cell. When the vesicle membrane fuses with the cell membrane, the vesicle releases it contents into the interstitial fluid. The vesicle membrane then becomes part of the cell membrane. Cells of the stomach and pancreas produce and secrete digestive enzymes through exocytosis Figure Endocrine cells produce and secrete hormones that are sent throughout the body, and certain immune cells produce and secrete large amounts of histamine, a chemical important for immune responses.

Cell: Cystic Fibrosis Cystic fibrosis CF affects approximately 30, people in the United States, with about 1, new cases reported each year. The genetic disease is most well known for its damage to the lungs, causing breathing difficulties and chronic lung infections, but it also affects the liver, pancreas, and intestines.

Only about 50 years ago, the prognosis for children born with CF was very grim—a life expectancy rarely over 10 years. Today, with advances in medical treatment, many CF patients live into their 30s. The symptoms of CF result from a malfunctioning membrane ion channel called the cystic fibrosis transmembrane conductance regulator, or CFTR. In healthy people, the CFTR protein is an integral membrane protein that transports Cl — ions out of the cell. In a person who has CF, the gene for the CFTR is mutated, thus, the cell manufactures a defective channel protein that typically is not incorporated into the membrane, but is instead degraded by the cell.

This characteristic puzzled researchers for a long time because the Cl — ions are actually flowing down their concentration gradient when transported out of cells. Active transport generally pumps ions against their concentration gradient, but the CFTR presents an exception to this rule. In normal lung tissue, the movement of Cl — out of the cell maintains a Cl — -rich, negatively charged environment immediately outside of the cell. This is particularly important in the epithelial lining of the respiratory system. Respiratory epithelial cells secrete mucus, which serves to trap dust, bacteria, and other debris.

Cilia on the epithelial cells move the mucus and its trapped particles up the airways away from the lungs and toward the outside. In order to be effectively moved upward, the mucus cannot be too viscous; rather it must have a thin, watery consistency. This is how, in a normal respiratory system, the mucus is kept sufficiently watered-down to be propelled out of the respiratory system. If the CFTR channel is absent, Cl — ions are not transported out of the cell in adequate numbers, thus preventing them from drawing positive ions.

The absence of ions in the secreted mucus results in the lack of a normal water concentration gradient. Thus, there is no osmotic pressure pulling water into the mucus. The resulting mucus is thick and sticky, and the ciliated epithelia cannot effectively remove it from the respiratory system. Passageways in the lungs become blocked with mucus, along with the debris it carries. A Human breast carcinoma: Z-Score is 4. B Human breast epithelial cells: Z-score is C Human breast carcinoma cell autoclave experiment: cells plated in media made with treated aqueous solution that was autoclaved prior to reconstitution.

Data were tested for normality by development of histograms and were found to be normal and were analyzed with two-tailed unpaired t-tests; mean control D Human breast carcinoma grown in media prepared on day 1 only and then used to replace media daily as opposed to using hypotonic saline solution treated daily by dc-DEP EMF and reconstituted daily. This shows a decrease in the growth inhibitory effect after day 4 when compared to Figure 2A where the media is prepared fresh daily.

In order to determine if the biological effects induced by the dc-DEP force EMF could be replicated without running dc through the device and by simply adding the metal salts noted in the first water analysis in Table 1 , we examined the ionic composition of the water before and after adding the metal salts to the same concentrations treated and after filtering of the metal salt water treated filtered Table 2.

Then ml were removed and placed in a clean plastic container and ml were removed and run through a 0. Percent change in the metal ion content between filtered and unfiltered solutions were calculated. We cultured MDA-MB cells in the DMEM with media that was reconstituted with a hypotonic saline solution that had chromium, nickel and molybdenum salts added to the same concentrations as found in the water analysis in Table 1 and the control groups were cultured in media that was reconstituted with the hypotonic saline solution that had not been treated with the dc-DEP force EMF system.

Figure 3. Metal Salt Experiments. A 3 mM saline solution that was identical to the solution used in all the previous experiments was made.

Instead of treating with the EMF, nickel, chromium and molybdenum salts were added to the hypotonic saline solution in order to achieve their same concentrations as found in the EMF treated-filtered water by the analysis of an independent laboratory. All two cell lines were cultured in standard media and the control and metal salts media were added to the wells on Day 2 and the media was made and replaced daily. Wells were also counted in triplicate daily. Data were analyzed with student's unpaired two-tailed t-tests.

A Human breast carcinoma; mean control B Human epithelial cells; mean control First we asked if there were differences in growth between cancerous and noncancerous cells in vitro when grown in the treated and control media. These initial experiments showed the unexpected finding of selective growth inhibition of only the cancerous cells in these two cell lines Figure 2A-B.

We found that conducting these experiments with only the addition of metal salts and no exposure to the dc-DEP force EMF showed no significant growth differences between the cancerous the noncancerous treated and control groups Figure 3A-B. The autoclaving of the hypotonic saline solution prior to reconstitution shows that exposure to the heat appears to nullify the growth inhibitory effect on cancerous cells and suggests a magnetic moment factor could be involved in these results Figure 2C.

Figure 4. Dielectrophoresis of Aqueous Metal Ions with the application of 3. Chloride is a known diamagnetic ion which maintains a negative charge while the other metal ions that were found in the water analysis of the hypotonic saline solution consisted of the positively charged cations: chromium, molybdenum, nickel and sodium Table 2. The 0. The dc-DEP force EMF from the BEFE device appears to both separate the ions and enhance the opposing orientations of the negatively charged chloride and positively charged sodium, chromium, nickel, and molybdenum ions in solution Figure 1.

This re-orientation of the ions in solution possibly allows the negatively charged diamagnetic chloride ions to exhibit both a strong attraction to the diamagnetic hydrophilic properties in the filter membrane and an opposing repulsion to help facilitate movement of the positively charged cations through the 0. The separation of all ions occurs first and then the ions will re-orient to those ions to which they are more similar and therefore more strongly attracted to diamagnetic-chloride ions attract to each other and to diamagnetic-water etc. Also as previously noted, when we tested the ion concentrations of the unfiltered and filtered hypotonic saline solutions that were used for the metal salt experiments, we found that the static charge on the cellulose acetate hydrophilic membrane did not attract the chloride ions that had not been exposed to the dc-DEP force EMF since they readily passed through the 0.

Figure 5. Cells were fixed and stained with DAPI to visualize the nuclei and with an anti-tubulin antibody followed by a rhodamine-conjugated secondary antibody. The human breast carcinoma cells were then grown in control or treated media for one day and were fixed and stained DAPI to visualize the nuclei and with an anti-tubulin antibody followed by a rhodamine-conjugated secondary antibody with fluorescent microscopy.

This data also suggests that exposure of the hypotonic saline solution to this dc-DEP force EMF creates a form of magnetic memory change or field effect in solution as well since the chloride ion completely filters out of the solution prior to reconstitution of growth media. The next question we asked was if this b Cl - completely filters out in the cellulose membrane, then how is this effect translated to these in vitro experiments? Sodium and molybdenum are paramagnetic metal ions and when these ions are exposed to an electromagnetic field, they form induced magnetic fields in the same direction as the field Stohr et al.

Chromium is an anti-ferromagnetic metal ion and it forms an anti-parallel spin that strengthens the field when in combination with parallel spin of the ferromagnetic nickel Camley et al. Ferromagnetic metals nickel are highly susceptible to magnetic fields and retain their magnetism even after the removal of the applied field, while anti-ferromagnetic metal ions tend to change their magnetic behaviors relative to the Neel temperature Ohno et al.

We will now discuss dc-DEP force EMF effects on membrane potential, cell volume, tubulin staining, transcription, translation and chloride ion channel expression Figures 1, Figure 6. The results shown are the means of cell size for days Since chloride ions are known to bind to actin and tubulin, we conducted tubulin staining of the MDA-MB cells which showed approximately 17 percent of the control cells in different stages of mitosis while no treated cells were found to be undergoing mitosis after one day of growth in the treated media Figure 5 Suh, ; Peretti et al. The MDA-MB treated groups showed an increase in cell size on days when compared to control and then appear to have a drop in cell size on day 6 Figure 6.

The MCFA cells measured larger than the MDA-MB cells when initially placed in the treated and control media, but overall kept uniform size between control and treated groups from day Figure 7. Chloride ion channels are also known to be regulators of Vmem. Since fluorescence methods are best suited for high-throughput identification of chloride-channel modulators, we conducted membrane potential analysis with a fluorescent assay Verkman and Galietta, Hyperpolarization of both cell lines was initially observed when exposed to treated media Figure 8.

Changes in the morphology and size of the cancer cells is also noted from phase contrast pictures after one day in treated and control growth media Figure 9. Figure 7. Further analysis show these cells are becoming apoptotic.

The Cell Membrane – Anatomy and Physiology

Microarray analysis identified 1, genes that were up-regulated over 2-fold and genes that were down-regulated over 2-fold in the treated groups grown in the media that was reconstituted with the dc-DEP force EMF-treated hypotonic saline solution compared to the non-treated human breast carcinoma. For comparison, transcripts showed over 2-fold changes in the dc-DEP force EMF-treated versus non-treated human epithelial cells.

There was also a significant increase in mRNA in the treated versus control groups in the human breast carcinoma which also suggests an increase in transcription is occurring in the treated versus control groups Figure Another significant up-regulation was noted in the serine and glycine biosynthesis pathways in both the human breast carcinoma and the human breast epithelial cells Figure It is interesting to note that glycine receptors and chloride channels are intricately linked Lynch, A t-RNA up-regulation of L-cysteine, L-glutamine, L-glutamate, L-alanine, L-tyrosine, L-tryptophan, L-serine, L-proline, L-glycine were also found in the human breast carcinoma and these changes suggests there may be an increase in the initiation of translation of the polypeptide chains on the ribosomes in the treated versus control human breast carcinoma.

These changes in gene expression of serine and glycine biosynthesis and initiation of translation could be sparked by the significant increase in chloride ion channel expression that is a by-product of the b Cl - influence on diamagnetic anisotrophy in the cell membranes. Figure 8. Membrane potential assay. The graphs show change in fluorescence over time. When a cell is depolarized the fluorescence increases and when it is hyperpolarized the fluorescence decreases.

These dyes are permeant and work by a mechanism involving potential-dependent follows cation flow redistribution of the charged dye between the medium and the inside of the cell, organelle or vesicle. Measurements were conducted to at 72 hours and both cell lines maintained in treated media remained in a more hyperpolarized state than controls. CLIC2 and CLIC4 code for chloride intracellular channel proteins and are members of the p64 family that bind to dynamin, tubulin, actin, and creatine kinase and were found to be upregulated by microarray analyses and subsequently validated by RT-qPCR Suh, ; Cromer, ; Peretti et al.

These families of ion channels are known to influence chloride transport, signaling, cytoskeleton integrity, mitosis, cytokinesis and differentiation functions etc. Also, CLIC4 codes for a diverse group of proteins that regulates cellular processes, such as stabilization of cell Vmem Peretti et al. No significant up-regulation of these 2 chloride channels expressions were found in the MCFA cells although expression was noted in both groups. Table 3.

Passive transport

Percent Change in Vmem of Treated vs. Chloride is a diamagnetic metal ion that appears to dissociate from its chloro-metabolites after exposure to the dc-DEP force EMF. The frequency emitted by this device appears to create a b Cl - that shows a strong affinity to the cellulose acetate filter that consists of properties similar to cell membranes Figure 4. The cell membrane exhibits a distinct diamagnetic anisotropy Iwasaka et al.

Structure and Composition of the Cell Membrane

Diamagnetic anisotropy occurs when a field operates in opposition to the applied field and is driven by that applied field. This data suggests that the diamagnetic negatively charged nature of b Cl - is attracted to the diamagnetic hydrophilic domain like attracts like of the filter and most likely the cell membrane possibly causing the spin states and fields from the b Cl - and water to operate in opposition to the positively charged spin states and fields of the paramagnetic, ferromagnetic and anti-ferromagnetic ions.

Chemical shifts involve diamagnetic anisotropy or opposing bi-directional flow of ions and molecules in the membranes of cells.

Table of Several Ion Channel Family Members

THE STUDY OF THE ANION TRANSPORT PROTEIN ('BAND 3 PROTEIN') IN THE RED CELL MEMBRANE BY MEANS OF TRITIATED 4. Chloride transport plays a fundamental role in all cells. However, it is in epithelial cells that chloride movement becomes critical to the primary specialized task of.

The ferromagnetism displayed by the nickel could explain how the applied field continues to exert dc-DEP force EMF in solution before waning after approximately 90 hours as seen in the growth inhibitory effects in Figure 2D. Figure 9.