Biomedical subjects

D C Chang

Publications and source records attributed to D C Chang.

At least 55 records · Page 3Linked to original sources

PubMed1991

Reorganization of cytoplasmic structures during cell fusion.

In order to provide a better understanding of the dynamic process of cell fusion, we studied the reorganization of cytoplasmic structures in electro-fused CV-1 cells. Using fluorescence microscopy and double staining methods, we examined correlations between the structural patterns of the major cytoskeletal proteins (microtubules, actin and vimentin intermediate filaments) and the distribution of various organelles (endoplasmic reticulum, mitochondria and nuclei) at different stages of cell fusion. Our results suggest that microtubules appear to play a primary role in the process of cytoplasmic reorganization. At the early stage of cell fusion, microtubules were observed to infiltrate rapidly into the newly formed cytoplasmic bridges and establish a connection between the cytoskeletal networks of fusing cells. The reorganization of microtubules was found to be correlated with the redistribution of endoplasmic reticulum (ER), vimentin intermediate filaments, mitochondria, and the aggregation of nuclei. The F-actin system, on the other hand, appeared to be independent of the reorganization of the other cytoplasmic structures. The principal function of F-actin during cell fusion is probably to widen the cytoplasmic bridges by lamellipodial extension.

Actins↗

PubMed1990

Dynamic changes of microtubule and actin structures in CV-1 cells during electrofusion.

To study the involvement of the cytoskeletal system in the fusion of animal cells, we examined the dynamic changes of cytoskeletal proteins during the various stages of cell fusion. CV-1 cells were fused by applying a radio-frequency electrical pulse. Structural changes of microtubules (MTs) and F-actin were monitored simultaneously by double-label fluorescence microscopy. It was observed that in a few minutes after the initiation of cell fusion, MT bundles began to extend into the cytoplasmic bridges which were formed by fusing the membranes of neighboring cells. Later, a network of parallel MT bundles appeared between the adjacent nuclei of the fusing cells; such MT bundles may provide the mechanical links that are responsible for nuclear aggregation. The structural changes of F-actin during cell fusion were more complicated. We observed many different patterns of actin distribution in the fusing cells, including some giant, ring-shaped structures. Reorganization of actin is unlikely to be involved in the nuclear aggregation process. Instead, actin bundles condensed at the cell edges may help to widen the cytoplasmic bridges to allow merging of cellular contents between the fusing cells.

Actins↗

PubMed1990

Changes in membrane structure induced by electroporation as revealed by rapid-freezing electron microscopy.

Cells can be transiently permeabilized by exposing them briefly to an intense electric field (a process called "electroporation"), but it is not clear what structural changes the electric field induces in the cell membrane. To determine whether membrane pores are actually created in the electropermeabilized cells, rapid-freezing electron microscopy was used to examine human red blood cells which were exposed to a radio-frequency electric field. Volcano-shaped membrane openings appeared in the freeze-fracture faces of electropermeabilized cell membranes at intervals as short as 3 ms after the electrical pulse. We suggest that these openings represent the membrane pathways which allow entry of macromolecules (such as DNA) during electroporation. The pore structures rapidly expand to 20-120 nm in diameter during the first 20 ms of electroporation, and after several seconds begin to shrink and reseal. The distribution of pore sizes and pore dynamics suggests that interactions between the membrane and the submembrane cytoskeleton may have an important role in the formation and resealing of pores.

Electric Stimulation↗

PubMed1990

Normalization of thyroid blood flow in Graves' hyperthyroidism following radioactive iodine therapy.

In a group of 12 patients with Graves' hyperthyroidism, administration of 514 +/- 43 (mean +/- SD) MBq iodine-131 was associated with a fall of superior thyroid artery (STA) blood flow in two at 6 months and in eight at 11 months. The reduction in time-averaged velocity at 11 months correlated with the reduction in FT4 (r = 0.72, P less than 0.01) and in FT3 (r = 0.64, P less than 0.025) at this time. In four patients who had persistent elevated STA blood flow, two were still hyperthyroid. The diameter of the STA was unchanged at 6 months and only half the patients had reduction of their STA size at 11 months after radioiodine (RAI) therapy. These data indicate that normalization of STA blood flow precedes normalization of STA size in patients treated with RAI. Further work is required to determine whether STA blood flow measurements are of predictive value in treatment outcome.

Aged↗

PubMed1989

Effects of pH on cell fusion induced by electric fields.

Electrofusion has recently become an important area of cell biology research. We studied the effects of pH of the cell medium on the electrofusion of human red blood cells. Cell fusion was monitored by observing the movement of a lipophylic dye between neighboring fused cells using a fluorescence microscope. The cells were first brought into close contact by dielectrophoresis. Fusion was then induced by three pulses of high-intensity electric field. Within minutes following the pulse application, many cells were observed to fuse together to form fusion chains of different lengths. We found that the optimal pH for cell fusion is around pH 7.5. At this pH, the fusion yield was highest (ranging from 57 to 81%) and the average number of cells within a fusion chain was also the largest. The dependence of cell fusion on pH is more sensitive at low than at high pH. The fusion yield was decreased by 40% when the pH was changed from 7.5 to 6.0, but there was only a 20% decrease in yield between pH 7.5 and 10.0. We suspect that the observed pH effects may be caused by a redistribution of fixed charges at the cell surface, or changes in amphipathicity of the surface proteins.

Cell Fusion↗

PubMed1989

Cell poration and cell fusion using an oscillating electric field.

It has been shown in previous studies that cell poration (i.e., reversible permeabilization of cell membrane) and cell fusion can be induced by applying a pulse (or pulses) of high-intensity DC (direct current) electric field. Recently we suggested that such electro-poration or electro-fusion can also be accomplished by using an oscillating electric field. The DC field relies solely on the dielectric breakdown of the cell membrane to induce cell fusion. The oscillating field, on the other hand, can produce not only a dielectric breakdown, but also a sonicating motion in the membrane that could result in a structural fatigue. Thus, a combination of a DC field and an oscillating field is expected to enhance the efficiency of cell poration and cell fusion. This study is an experimental test of such an idea. Here, pulses of high-intensity, DC-shifted RF (radio frequency) electric field were used to induce cell poration and cell fusion. The fusion experiments were done on human red blood cells. The poration experiments were done on a fibroblast cell line using a molecular probe (which is a DNA plasmid containing the marker gene chloramphenicol acetyltransferase, CAT) and assayed by a gene transfection technique. It was found that the pulsed RF field is highly efficient in both cell fusion and cell poration. Also, in comparison with electro-poration using a DC field, the RF field results in a higher percentage of cells surviving the exposure to the electric field.

Cell Fusion↗

PubMed1988

K+-selective microelectrode study of internally dialyzed squid giant axons.

Intracellular potassium activity, (aK)i, and axoplasmic K+ concentration, [K+]i, were measured by means of K+-selective microelectrodes and atomic absorption spectroscopy, respectively, in squid giant axons dialyzed with K+-free dialysis solution and bathed in K+-free artificial sea water. (aK)i measurements indicated that axoplasmic free K+ could be depleted by dialysis, whereas [K+]i measurements on axoplasm extruded from these axons suggest substantial retention of K+ (15.5 +/- 1.7 mmol/kg axoplasm K+; n = 9). In comparison, [K+]i in axoplasm extruded from freshly dissected axons was 330 +/- 16 mmol/kg axoplasm (n = 6). These data suggest that approximately 5% of the axoplasmic K+ ions are not easily removed by dialysis and that these ions are either bound to macromolecular sites or sequestered into membrane-enclosed organelles.

Animals↗

PubMed1988

Estimates for the partial differential-Neumann problem for pseudoconvex domains in C of finite type.

We outline results obtained for the partial differential-Neumann problem for an arbitrary pseudoconvex domain in C(2) of finite type. We obtain an approximation to the Neumann operator. A number of sharp estimates for the solution of partial differentialu = f are a consequence; one of these is an extension of the L(1) estimate of Henkin and Skoda used to characterize the zero sets of functions of the Nevanlinna class.

Journal Article↗

PubMed1987

The effect of preoperative Lugol's iodine on thyroid blood flow in patients with Graves' hyperthyroidism.

A study was conducted to investigate the effect of Lugol's iodine on the superior thyroid artery (STA) blood flow with use of a Duplex ultrasound scanner for 12 patients with Graves' disease. All patients were treated with antithyroid drugs until they were euthyroid and then, with randomization, the patients received either Lugol's iodine, 0.3 ml thrice daily, or placebo for 9 days in a double-blind fashion. Antithyroid drugs were continued throughout the study. Reduction in the diameter, time-averaged velocity (TAV), and volume flow (VF) of the STAs was demonstrated in all patients in the treatment group, whereas there were no consistent trends in the placebo group. The changes in TAV and VF were significantly different between the placebo and treatment groups (p less than 0.01 for TAV and p less than 0.005 for VF). These changes were more marked in patients with high initial VF and minimal in patients with low initial VF. On the basis of these results, we recommend that patients with high thyroid blood flow before thyroidectomy should receive Lugol's iodine preoperatively.

Adult↗

PubMed1986

Axonal transport and the movement of 45Ca inside the giant axon of squid.

45Ca was microinjected directly into the giant axon of squid, and the radioisotope profile along the axon was determined after 2-12 h. Our results indicated that the intracellular Ca ions at the axon, unlike those at the cell body, were not axonally transported at a fast rate. The implication of this finding on the involvement of Ca in the axonal transport system is discussed.

Animals↗

PubMed1986

Ultrastructure of the squid axon membrane as revealed by freeze-fracture electron microscopy.

The structure of the axolemma of the squid giant axon was studied by freeze-fracture electron microscopy. Three types of preparations were examined: intact axons, axons with their Schwann cell sheaths stripped off prior to freezing, and axons with their Schwann cell sheaths chemically detached but not mechanically removed. Because of a problem of cross-fracturing, the first two types of preparations revealed very few membrane faces of the axolemma. This cross-fracturing problem, however, was eliminated when we used a complementary replication method to fracture the third type of preparation. We found that the E-face of the axon membrane was smooth relative to the P-face, which showed many prominent intramembrane particles (IMP). The diameters of the typical IMP range from 6 to 15 nm. The P-face of the adjacent Schwann cells also showed many large IMP. The sizes and heights of the Schwann-cell IMP, however, appear to be more homogeneous than the P-face axolemma.

Animals↗

PubMed1986

Is the K permeability of the resting membrane controlled by the excitable K channel?

To test whether or not the potassium permeability of the resting membrane is controlled by the excitable K channels (delayed rectifier), we examined changes in the Na and K permeability ratio, PNa/PK, of the squid axon before and after the excitable K channels were blocked. The blockage of the K channels was accomplished by three independent methods: internal application of tetraethylammonium, internal application of 4-aminopyridine plus Cs, and prolong internal perfusion of NaF solution. The permeability ratio was determined using two different methods: the conventional electrophysiological method and a new method based on the measurements of the hyperpolarizing effect of Na removal. We found that blocking the K channels did not cause a proportional decrease in the K permeability of the resting membrane, suggesting that the semipermeable property of the resting membrane is not determined by the excitable K channels.

Animals↗

PubMed1985

A comparative study of the effects of tetrodotoxin and the removal of external Na+ on the resting potential: evidence of separate pathways for the resting and excitable Na currents in squid axon.

To investigate whether the Na permeability of the resting membrane is determined predominantly by the excitable Na channel, we examined the effects of tetrodotoxin (TTX) and the complete removal of external Na+ on the resting potential. In the intact squid axon bathed in K-free artificial seawater, both TTX and the removal of Na+ produced small hyperpolarizations. The effect of Na removal, however, was larger than that of TTX. In the perfused squid axon, the hyperpolarization produced by the removal of external Na+ was greatly enhanced when the internal K concentration ([K+]i) was reduced. The effect of TTX, on the other hand, was not sensitive to the [K+]i or to the membrane potential. For [K+]i = 50 mM and [K+]o = 0, the average hyperpolarization produced by TTX was 1.2 mV, while the hyperpolarization produced by Na removal was approximately 21 mV. The difference between these two effects suggests that the majority of the resting Na current passes through pathways other than the excitable Na channel.

Animals↗

PubMed1985

Transport of Na+ inside the giant axon of squid.

The transport mechanism of Na ions within the nerve cell was studied by measuring the radioactivity distribution profile of 22Na that had been intracellularly injected into the giant axon. Specifically, we tested whether or not the movement of Na ions is coupled with the process of "fast axonal transport." Results of our measurements indicate that the intracellular transport of Na+ and the fast axonal transport are two independent processes. Very few Na ions are irreversibly sequestered into the axoplasmic vesicles involved in axonal transport. The movement of Na+ inside the axon can be modeled by a one-dimension diffusion. The effective diffusion coefficient of the intracellular Na+ was determined in this study.

Animals↗

PubMed1983

A voltage-clamp study of the effects of colchicine on the squid giant axon.

The effects of colchicine applied inside a squid giant axon were studied using voltage-clamp and internal perfusion techniques. It was found that colchicine selectively and reversibly suppresses the sodium conductance during excitation. The possible involvement of the microtubular structure in the functioning of the excitable channel is discussed.

Animals↗

PubMed1983

Dependence of cellular potential on ionic concentrations. Data supporting a modification of the constant field equation.

The resting potential in the squid axon has been measured at various concentrations of Cl, K, Na, and Ca ions. The results of these measurements are compared with the Goldman-Hodgkin-Katz (GHK) equation and a modified constant field equation. This modified equation was derived by including currents carried by divalent ions and the effects of the unstirred layer and the periaxonal space. It is shown that, although the GHK equation can fit the V vs. [K]o data well, it has difficulty explaining the observed dependence of V on [Na]o when the axon is bathed in K-free artificial sea water. The use of the modified constant field equation removes this difficulty.

Animals↗

PubMed1982

Microtubule complexes correlated with growth rate and water proton relaxation times in human breast cancer cells.

Ten established human breast cancer cell lines display patterns of microtubule organization which are characterized by growth rate of the cell populations and the freedom of mobility of cellular water molecules measured by nuclear magnetic resonance spectroscopy. Cell lines with population-doubling times of 1 to 2 days demonstrate rapid mobility of water molecules by proton spin-lattice and spin-spin relaxation times (T1 greater than 750 msec, T2 greater than 120 msec) and have diffuse patterns of tubulin immunofluorescent antibody staining. Moderately fast dividing cells (population-doubling times of 3 to 7 days) have T1 values of 600 to 750 msec and show approximately 50% organized complexes of polymerized microtubules in the cytoplasm. Slow-growing cell lines demonstrate more restricted mobility of water molecules (T1 values of 500 to 600 msec) and contain abundant networks of polymerized microtubules. The three-way correlation of the physical parameter of water proton relaxation times, the structural parameter of microtubule organization, and the physiological parameter of growth suggest a close interaction of water molecules with the cytoplasmic macromolecular network in the performance of physiological function.

Body Water↗

PubMed1981

Nuclear magnetic resonance study of muscle water protons in muscular dystrophy of chickens.

Using the pulsed nuclear magnetic resonance (NMR) spectroscopy, the spin-lattice (T1) and the spin-spin (T2) relaxations times of water protons from samples of pectoralis major muscles of normal (line 412) and homozygous dystrophic (line 413) chickens were measured. Both the T1 and T2 were significantly increased (P less than 0.05) in the dystrophic muscles. The mean values of the relaxation times are given +/- S.D. The T1 values were 654 +/- 22 msec in normal and 692 +/- 41 msec in dystrophic muscles. The T2 values for normal and dystrophic muscles were 39 +/- 4 msec and 52 +/- 7 msec, respectively. Although the water content of dystrophic muscles (78.9 +/- 0.6%) determined by gravimetric methods was significantly higher than normal muscles (74.9 +/- 1.1%), this difference in tissue hydration could not explain quantitatively the increase of T1 and T2 values in the dystrophic muscles. The results of the measurements of the relaxation times seem to suggest that there are changes in the composition and/or conformational state of the proteins.

Animals↗