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Biomedical subjects

M S Cooper

Publications and source records attributed to M S Cooper.

At least 19 recordsLinked to original sources
PubMed1995

Membrane potential perturbations induced in tissue cells by pulsed electric fields.

Pulsed electric fields directly influence the electrophysiology of tissue cells by transiently perturbing their transmembrane potential. To determine the magnitude and time course of this interaction, electrotonic cable theory was used to calculate the membrane potential perturbations induced in tissue cells by a spatially uniform, pulsed electric field. Analytic solutions were obtained that predict shifts in membrane potential along the length of cells as a function of time in response to an electrical pulse. For elongated tissue cells, or groups of tissue cells that are coupled electrotonically by gap junctions, significant hyperpolarizations and depolarizations can result from millisecond applications of electric fields with strengths on the order of 10-100 mV/cm. The results illustrate the importance of considering cellular cable parameters in assessing the effects of transient electric fields on biological systems, as well as in predicting the efficacy of pulsed electric fields in medical treatments.

Animals↗
PubMed1995

Intercellular signaling in neuronal-glial networks.

Glial cells have recently been found to exhibit electrophysiological and metabolic responses to many neurotransmitters and neuromodulators. These findings have focused attention on the possibility that active signaling between neurons and glia could represent an important form of intercellular communication within the brain. Since glial and neuronal networks are both physically and metabolically interlinked, such intercellular signaling may represent a mechanism for inducing collective changes in the cellular physiology of neuronal and glial cell populations. Within the nervous tissue of both vertebrate and invertebrate organisms, glial cells are known to secrete extracellular signal molecules, modulate carbohydrate metabolism, and control the volume and ionic composition of extracellular space. In this paper, the roles that cytoplasmic [Ca2+] transients may play in regulating these glial cell functions are reviewed. Mechanisms by which intracellular Ca oscillations and intercellular Ca waves may be generated in neurotransmitter-stimulated glial cells are also discussed. In addition, it is proposed that rhythmic glial cell contractions and shape changes, which have been observed for many decades, are linked to Ca-induced secretion of ions, water, and neuroactive compounds. These activities represent mechanisms by which Ca-induced changes in glial cell physiology could potentially alter the excitability of neuronal networks.

Animals↗
PubMed1990

Tubulovesicular processes emerge from trans-Golgi cisternae, extend along microtubules, and interlink adjacent trans-golgi elements into a reticulum.

Morphological dynamics and membrane transport within the living Golgi apparatus of astrocytes labeled with NBD-ceramide were imaged using both electronically enhanced fluorescence video and laser confocal microscopy. In time-lapse recordings, continuous tubulovesicular processes are observed to emerge from trans-Golgi elements and extend along microtubules at average rates of 0.4 microns/s. In addition, discrete fluorescent particles are observed to emerge from the trans-Golgi and subsequently migrate along microtubules at comparable velocities. Frequently, tubulovesicular processes form stable connections that interlink adjacent trans-Golgi elements into an extensive reticulum. Laser photobleaching-recovery experiments reveal that tubulovesicular processes can provide direct pathways for the diffusion of membrane lipids between joined trans-Golgi elements. These results suggest that microtubule-based transport and membrane fusion can operate to interconnect certain cisternal membranes of adjacent Golgi elements within the cell.

Animals↗
PubMed1990

Glutamate induces calcium waves in cultured astrocytes: long-range glial signaling.

The finding that astrocytes possess glutamate-sensitive ion channels hinted at a previously unrecognized signaling role for these cells. Now it is reported that cultured hippocampal astrocytes can respond to glutamate with a prompt and oscillatory elevation of cytoplasmic free calcium, visible through use of the fluorescent calcium indicator fluo-3. Two types of glutamate receptor--one preferring quisqualate and releasing calcium from intracellular stores and the other preferring kainate and promoting surface-membrane calcium influx--appear to be involved. Moreover, glutamate-induced increases in cytoplasmic free calcium frequently propagate as waves within the cytoplasm of individual astrocytes and between adjacent astrocytes in confluent cultures. These propagating waves of calcium suggest that networks of astrocytes may constitute a long-range signaling system within the brain.

Aniline Compounds↗
PubMed1989

Cell intercalation during notochord development in Xenopus laevis.

Morphometric data from scanning electron micrographs (SEM) of cells in intact embryos and high-resolution time-lapse recordings of cell behavior in cultured explants were used to analyze the cellular events underlying the morphogenesis of the notochord during gastrulation and neurulation of Xenopus laevis. The notochord becomes longer, narrower, and thicker as it changes its shape and arrangement and as more cells are added at the posterior end. The events of notochord development fall into three phases. In the first phase, occurring in the late gastrula, the cells of the notochord become distinct from those of the somitic mesoderm on either side. Boundaries form between the two tissues, as motile activity at the boundary is replaced by stabilizing lamelliform protrusions in the plane of the boundary. In the second phase, spanning the late gastrula and early neurula, cell intercalation causes the notochord to narrow, thicken, and lengthen. Its cells elongate and align mediolaterally as they rearrange. Both protrusive activity and its effectiveness are biased: the anterioposterior (AP) margins of the cells advance and retract but produce much less translocation than the more active left and right ends. The cell surfaces composing the lateral boundaries of the notochord remain inactive. In the last phase, lasting from the mid- to late neurula stage, the increasingly flattened cells spread at all their interior margins, transforming the notochord into a cylindrical structure resembling a stack of pizza slices. The notochord is also lengthened by the addition of cells to its posterior end from the circumblastoporal ring of mesoderm. Our results show that directional cell movements underlie cell intercalation and raise specific questions about the cell polarity, contact behavior, and mechanics underlying these movements. They also demonstrate that the notochord is built by several distinct but carefully coordinated processes, each working within a well-defined geometric and mechanical environment.

Animals↗
PubMed1989

Electrophoretic repatterning of charged cytoplasmic molecules within tissues coupled by gap junctions by externally applied electric fields.

Ionic currents and cytoplasmic voltage gradients have been observed in a variety of polarizing cells and developing tissues. In certain cases, it has been determined that these endogenous electric fields can segregate intracellular charged molecules by electrophoresis; in other cases, the endogenous fields are suspected to have such an influence. Separate theoretical suggestions have been made that extracellular electric currents, whether from a biological or a nonbiological source, should be able to electrophorese intracellular molecules after being conducted through cell membranes into the interior of long single cells [L.F. Jaffe and R. Nuccitelli (1977) Annu. Rev. Biophys. Bioeng. 6, 445-476] or extended ensembles of cells coupled electrotonically by gap junctions [M.S. Cooper (1984) J. Theor. Biol. 111, 123-130]. To test whether external electric fields could redistribute intracellular molecules within a tissue coupled by gap junctions, and to quantitatively measure in situ the electrophoretic mobility of a charged intracellular molecule, we injected 6-carboxyfluorescein into the electrotonically coupled lateral giant neurons of the crayfish abdominal nerve cord. When a dc electric field (0.2-3.4 V/cm) was subsequently applied along the length of the cord, the negatively charged fluorescent dye was observed to migrate through both the cytoplasms and the gap junctions of the lateral giant neurons, toward the anode, at a rate directly proportional to the applied electric field strength (electrophoretic mobility = -0.92 +/- 0.27 micron/sec per V/cm). These results suggest that electric fields of a sufficient magnitude, whether of an exogenous or an endogenous origin, can repattern the distribution of charged molecules within the cytoplasm of an extended ensemble of coupled cells. In addition, these results suggest that externally applied electric fields might be used in studies of pattern formation to repattern the intercellular distribution of charged molecules that are permeant to gap junctions within electrically coupled tissues.

Animals↗
PubMed1986

Motility of cultured fish epidermal cells in the presence and absence of direct current electric fields.

The motile behavior and cytoskeletal structures of fish epidermal cells (keratocytes) in the presence and absence of direct current (DC) electric fields were examined. These cells spontaneously show highly directional locomotion in culture, migrating at rates of up to 1 micron/s. When DC electric fields between 0.5 and 15 V/cm are applied, single epidermal cells as well as cell clusters and cell sheets migrate towards the cathode. Cell clusters and sheets break apart into single migratory cells in the upper range of these field strengths. Cell shape and morphology are unaltered when the keratocytes are guided by an electric field. Neither the spontaneous locomotion nor the electrically guided motility were found to be microtubule dependent. 1 mM La3+, 10 mM Co2+, 50 microM verapamil, and 50 microM nitrendipine (calcium channel antagonists) reversibly inhibited lamellipod formation and cell locomotion in both spontaneously migrating and electrically guided cells. Ciba-Geigy Product 28392, which stimulates the opening of calcium channels, and is a competitive inhibitor of nitrendipine, has no effect on the locomotion of keratocytes. Cell motility was also unaffected by hyperpolarizing and depolarizing (low and high K+) media. It is argued that while a tissue cell may accommodate changes in resting membrane potential without becoming more or less motile, the cell may not be able to counterbalance the effects of depolarization and hyperpolarization simultaneously. In this context, a gradient of membrane potential, which is induced by an external DC electric field, will serve as a persistent stimulus for cell locomotion.

Animals↗
PubMed1985

Electrical and ionic controls of tissue cell locomotion in DC electric fields.

The motility of fish epidermal cells (keratocytes) was examined in the presence and absence of DC electric fields. In fields of 0.5-15 V/cm, single epidermal cells, cell clusters, and cell sheets migrate toward the cathode. Cell clusters and sheets break apart into single migratory cells in the upper range of these field strengths. During locomotion, keratocytes extend broad lamellipodia, which contain a pervasive actomyosin network. The lamellipodial extension and locomotion of keratocytes are reversibly inhibited by a variety of calcium channel antagonists, whereas their motility is unaffected by hyperpolarizing and depolarizing (low and high K+) media. Microtubule disassembly has no effect on cell morphology, motility or the ability of the cells to be guided by a DC electric field. Using these results, the role that membrane-regulated Ca2+ influx may play in generating cytoskeletal and protrusive activity in keratocytes and other cells is discussed in some detail. Mechanisms by which an external electric field may bias transmembrane ion fluxes and thereby control cell locomotion are also examined.

Animals↗
PubMed1984

Gap junctions increase the sensitivity of tissue cells to exogenous electric fields.

Cells coupled by gap junctions will react as a single unit to an applied electric field. In a given field, the hyperpolarization and depolarization of cell membranes at the ends of an electrotonically coupled tissue are increases by a factor of 10-100 over single, uncoupled cells. Gap junctional coupling therefore increases the likelihood that cells are influenced by the weak electric fields which are commonly found in developing and regenerating tissues.

Amphibians↗
PubMed1984

Perpendicular orientation and directional migration of amphibian neural crest cells in dc electrical fields.

The behavior of cultured neural crest cells of Ambystoma mexicanum and Xenopus laevis in dc electrical fields was studied. In fields of 1-5 V/cm, isolated or confluent cells retract both their anode- and cathode-facing margins. Subsequently, the cells elongate, with protrusive activity confined to their narrow ends. In larger fields (greater than or equal to 5 V/cm), protrusions form on the cathode-facing sides of the perpendicularly oriented cells. The cells then begin migrating laterally, perpendicular to their long axes, towards the cathode. We suggest that the perpendicular alignment and cathode-directed migrations result from cytoskeletal changes mediated by modified ion fluxes through the anode-facing (hyperpolarized) and cathode-facing (depolarized) cell membranes. The breaking of cellular confluence in response to dc electric fields is also discussed.

Ambystoma↗
PubMed1980

Spectroscopic evidence for strong oscillating and static dielectric polarizations in malignant cells.

Analysis of splitting and shifting of malignant cell (mammary carcinoma and virally transformed cells) Raman and microwave spectral lines suggests that the Raman line splittings are due to non-linear second-order coupling of a coherently excited optical polarization wave with other polarization modes within these malignant cells. The microwave splittings are believed due to the non-linear second-order coupling effects of a lower frequency acoustic wave. The spectral line shiftings are believed indicative of a strong static dielectric polarization (ferroelectric state) of the cells.

Animals↗
PubMed1979

Long-range dielectric aspects of the eukaryotic cell cycle.

The phases of the eukaryotic cell cycle are described in terms of H. Fröhlich's theory of long-range coherence in biological systems. A phonon condensation is believed to initiate the S phase of the cycle. Following this event, an increasing polarization of the cell should occur, resulting in a phase transition to a metastable ferroelectric state at the beginning of mitosis. This polarized state is expected to be dissipated after mitosis is completed. It is believed that malignant cells possess a ferroelectric state throughout their life cycles.

Animals↗