Electro-osmosis at the surface of phospholipid bilayer membranes

Bioelectric potential gradients may initiate cell cycling: ELF and zeta potential gradients may mimic this effect

When a number of experimental studies in bioelectromagnetics were reviewed, those in which weak, exogenous extremely low frequency (ELF) fields were applied in fixed juxtaposition to their target tissues, were found to initiate mitogenesis or mitogenesis-related signals more successfully than when the target tissue moved freely during the irradiation. It is suggested that ELF fields in fixed juxtaposition to their target tissue and implanted foreign bodies or endogenous tissues with a significant zeta potential, mimic bioelectric fields generated at wounds. When the potential is high enough, they assist healing by moving cells into the wound and stimulating quiescent cells at the wound margin to cycle. Electrophoresis may help the initial migration of cells into the wound to form a clot, and migration of fibroblasts and epithelial cells from the wound margin. When exposed for a long time in a fixed juxtaposition to a potential gradient too weak to show in situ microelectrophoresis along the cell membrane surface, surface particles may coalesce to form microclusters, where like-charged surface particles are in close proximity, and growth factor receptor oligomerization and other cycle-initiating reactions are facilitated.

Carcinogenesis and initiation of cell cycling by charge-induced membrane clusters may be due to mitogen receptors and Na+/H+ antiports

The membrane cluster hypothesis of mitogenesis and carcinogenesis is extended by proposing that much of the Na+ ingress across a cell's plasma membrane at surface charge-induced (SCI) aggregates is due to mitogen-induced activation of Na+/H+ antiports. Intrinsic proteins (including mitogen receptors and antiports) are electrostatically attracted to and become part of the aggregate. In this location, close proximity facilitates antiport activation. Resulting Na+ ingress may cause sustained partial depolarization, cytoplasmic alkalinization, and initiation of cell cycling. Chronic phosphorylation-dephosphorylation at SCI aggregates too weak to induce cycling, may slowly form polyionic bonds between adjacent proteins at the inner lipid layer. These bonds convert the SCI aggregates to 'permanent' clusters that pass to a daughter cell with parental plasma membrane at mitosis, and are associated with malignancy. EGF and PDGF growth factors are used to develop the hypothesis, which is also applied to steroid and dioxin receptors and to oncogene products.

The membrane cluster hypothesis of mitogenesis and carcinogenesis

This paper modifies and extends an earlier one on the same subject. It explains why external (but not internal) surface molecules of plasma membrane clusters may be rapidly scattered by any external challenging bioelectrical field. Temporary clusters from challenges may induce mitosis in cells near wounds and in epithelial stem cells. Weak challenges of much longer duration may initiate carcinogenesis by permanent clusters. Basic intracellular ligand/receptors or oncogene products in sufficient concentration at the membrane inner lipid layer may form permanent clusters rapidly. Additive increase of inner surface clusters by initiating agents is equated to promotion; accelerated cluster growth to progression. As a malignant cell grows, its cluster population increases until its membrane becomes permeable enough to stimulate mitosis. A progression mechanism is suggested that is consistent with the known properties of ras p21 proteins. The effect of long term exposure to power transmission line fields on mitosis and carcinogenesis is discussed. An approach to anticancer therapy is suggested, using a hypothesis-based mechanism for the anti-cancer activity of retinoic acid.

Cell proliferation and carcinogenesis may share a common basis of permeable plasma membrane clusters

Wound potentials increase the surface potential of exposed areas of nearby cells. In these cells, soluble cytoplasmic bases are assumed gradually to move nearer the exposed area. Acidic molecules on the cell surface migrate to points opposite the bases. The image-charged species are mutually attracted to form transmembrane clusters. At clusters, membrane permeability increases and the cell is stimulated to cycle. When the wound heals, its clusters disperse, leaving a small 'permanent' residuum. Permanent clusters initiate cells to malignancy. They have (or develop) lipophilic molecules on both surfaces that help fix them in the membrane. Exposed cells contaminated with polycyclic aromatic hydrocarbon carcinogens (PAH) readily form permanent clusters. At mitosis, clusters on parental plasma membrane pass with that membrane to a daughter cell. Promotion results from many short-term or a single long-term exposure of initiated membranes to abnormal surface charge. Permanent clusters increase on the membrane after repeated wounding, proximity of charged foreign bodies like plastic film or asbestos, or oxidation of surface molecules. Progression requires acceleration of cluster growth so the daughter cell membranes become as leaky at maturity as was the parent membrane. One mechanism suggested involves reversible phosphorylation by membrane-bound kinases; another involves attraction of a basic protein (p36) to the membrane.

Membrane electroporation--fast molecular exchange by electroosmosis

Human and rabbit erythrocyte ghosts loaded with FITC-dextran (mol. mass = 10 kDa) and NBD-glucosamine (mol. mass = 342 Da) in buffers of different ionic strength and composition were subjected to electric pulses (intensity 0.7 kV/mm and decay half-time 1 ms) at 7-10 degrees C and 20-24 degrees C. The transfer of the fluorescent dyes from the interior of the ghosts through the electropores was observed by low light level video microscopy. The pulses caused the fluorescence to appear outside the membranes as a transient cylindrical cloud directed toward the negative electrode during the first video frame (17 ms). It was similar in both rabbit and human erythrocyte ghosts and at both temperatures but differs for the two dyes, the fluorescence cylinder is long and tall for the FITC-dextran and relatively short and thick for the NBD-glucosamine. The molecular exchange was 2-3 orders of magnitude faster within the first 17 ms after the pulse than the diffusional exchange. It decreased with increasing ionic strength. Formulae for the transfer of molecules by electroosmotic flow through the pores are in agreement with these observations. They allow estimation of the total area of pores with radii larger than that of the fluorescent dye during the pulse. The major conclusion is that electroosmosis is the dominating mechanism of molecular exchange in electroporation of erythrocyte ghosts.

Fusion events and nonfusion contents mixing events induced in erythrocyte ghosts by an electric pulse

The mechanism of membrane fusion was studied by using human erythrocyte ghosts held in close contact by alternating current-induced dielectrophoresis and inducing fusion with a single electric field pulse. Individual fusion events were followed visually using either 1,1'-dihexadecyl-3,3,3',3'-tetramethylindo carbocyanine perchlorate as a membrane-mixing label or 10-kD fluorescein isothiocyanate-dextran as a contents-mixing label. However, over a range of variables, the number of contents-mixing events usually considerably exceeded the number of membrane-mixing events, although the discrepancy was less at higher ionic strength. However, when the dielectrophoretic force holding the membranes in contact was turned off after the pulse, Brownian motion caused some of the groups of ghosts in which contents mixing occurred to eventually separate from one another, showing that they could not represent fusion events. Separate experiments showed, conversely, that fusion did occur in the groups that did not separate after the dielectrophoresis was turned off.

Electrokinetic shape changes of cochlear outer hair cells

Rapid mechanical changes have been associated with electrical activity in a variety of non-muscle excitable cells. Recently, mechanical changes have been reported in cochlear hair cells. Here we describe electrically evoked mechanical changes in isolated cochlear outer hair cells (OHCs) with characteristics which suggest that direct electrokinetic phenomena are implicated in the response. OHCs make up one of two mechanosensitive hair cell populations in the mammalian cochlea; their role may be to modulate the micromechanical properties of the hearing organ through mechanical feedback mechanisms. In the experiments described here, we applied sinusoidally modulated electrical potentials across isolated OHCs; this produced oscillatory elongation and shortening of the cells and oscillatory displacements of intracellular organelles. The movements were a function of the direction and strength of the electrical field, were inversely related to the ionic concentration of the medium, and occurred in the presence of metabolic uncouplers. The cylindrical shape of the OHCs and the presence of a system of membranes within the cytoplasm--laminated cisternae--may provide the anatomical substrate for electrokinetic phenomena such as electro-osmosis.

Electro-osmosis and the reabsorption of fluid in renal proximal tubules

The lateral intercellular spaces (LIS) are believed to be the final common pathway for fluid reabsorption from the renal proximal tubule. We postulate that electrogenic sodium pumps in the lateral membranes produce an electrical potential within the LIS, that the lateral membranes bear a net negative charge, and that fluid moves parallel to these membranes because of Helmholtz-type electro-osmosis, the field-induced movement of fluid adjacent to a charged surface. Our theoretical analysis indicates that the sodium pumps produce a longitudinal electric field of the order of 1 V/cm in the LIS. Our experimental measurements demonstrate that the electrophoretic mobility of rat renal basolateral membrane vesicles is 1 micron/s per V/cm, which is also the electro-osmotic fluid velocity in the LIS produced by a unit electric field. Thus, the fluid velocity in the LIS due to electro-osmosis should be of the order of 1 micron/s, which is sufficient to account for the observed reabsorption of fluid from renal proximal tubules. Several experimentally testable predictions emerge from our model. First, the pressure in the LIS need not increase when fluid is transported. Thus, the LIS of mammalian proximal tubules need not swell during fluid transport, a prediction consistent with the observations of Burg and Grantham (1971, Membranes and Ion Transport, pp. 49-77). Second, the reabsorption of fluid is predicted to cease when the lumen is clamped to a negative voltage. Our analysis predicts that a voltage of -15 mV will cause fluid to be secreted into the Necturus proximal tubule, a prediction consistent with the observations of Spring and Paganelli (1972, J. Gen. Physiol., 60:181).