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Biomedical subjects

D C Chang

Publications and source records attributed to D C Chang.

At least 73 records · Page 4Linked to original sources
PubMed1980

Nuclear magnetic resonance study of squid giant axon.

Using a spin-echo technique, the spin-lattice and spin-spin relaxation times (T1 and T2) of water protons in a single nerve fiber (giant axon of squid) were determined. Similar measurements were also carried out on axoplasm extruded from these nerve fibers. It was found that the relaxation times of water protons of both the intact fiber and the extruded axoplasm are approximately equal (and much less than those of a free solution), suggesting that the relaxation times of cellular water are shortened mainly by water-protein interactions rather than by water-membrane interactions.

Animals↗
PubMed1980

Intracellular concentration of elements in normal and dystrophic skeletal muscles of the chicken.

In this study, the intracellular concentrations of six elements (mmole/kg dry weight) were directly measured in the muscle fibers of pectoralis major muscles of eight week old, genetically dystrophic and normal chickens by the X-ray microanalysis technique. The extent of muscle degeneration was evaluated by morphometric measurements of muscle fiber diameter and other histological changes. A significant increase in the concentration of intracellular sodium and chlorine was evident in dystrophic muscles. The concentration of intracellular sodium was 127.0 +/- 35.0 in the muscle fibers of dystrophic chicks compared to 65.7 +/- 16.5 in normal controls. The concentration of chlorine was 90.5 +/- 27.5 and 54.1 +/- 5.5 in the muscle fibers of dystrophic and normal chicks respectively. The intracellular concentrations of potassium, magnesium, phosphorous, and sulfur remained unchanged in the dystrophic condition. Morphometric studies revealed that the dystrophic pectoralis muscles contain fewer but thicker fibers per unit area compared to normal pectoralis muscles. The importance of these findings are discussed in relation to the results of earlier investigations.

Animals↗
PubMed1980

Study of anisotropy in nuclear magnetic resonance relaxation times of water protons in skeletal muscle.

The anisotropy of the spin-lattice relaxation time (T1) and the spin-spin relaxation times (T2) of water protons in skeletal muscle tissue have been studied by the spin-echo technique. Both T1 and T2 have been measured for the water protons of the tibialis anterior muscle of mature male rats for theta = 0, 55, and 90 degrees, where theta is the orientation of the muscle fiber with respect to the static field. The anisotropy in T1 and T2 has been measured at temperatures of 28, -5 and -10 degrees C. No significant anisotropy was observed in the T1 of the tissue water, while an average anisotropy of approximately 5% was observed in T2 at room temperature. The average anisotropy of T2 at -5 and -10 degrees C was found to be approximately 2 and 1.3%, respectively.

Animals↗
PubMed1980

Distinction of normal, preneoplastic, and neoplastic mouse mammary primary cell cultures by water nuclear magnetic resonance relaxation times.

Normal, preneoplastic, and neoplastic primary cultures of mouse mammary epithelial cells were distinguishable on the basis of water proton nuclear magnetic resonance (NMR) relaxation times--i.e., spin-lattice relaxation time (T1) and spin-spin relaxation time (T2). T1 values were 916 +/- 24 msec for normal cells, 1,029 +/- 24 msec for preneoplastic cells, and 1,155 +/- 42 msec for neoplastic cells. This method of distinction between normal and neoplastic cells (P less than 0.001) and normal and preneoplastic cells (P less than 0.005) supported previous findings in whole tissues. NMR relaxation times resulted in better distinction between these cell populations than any other technique except direct histology. The T1 and T2 values of water protons in cells grown in primary culture were higher than those of established mouse mammary cancer cell lines. The differences in T1 and T2 did not correlate with cellular hydration. The data suggested a basic difference in water-macromolecular surface interactions among normal, preneoplastic, and neoplastic cells.

Animals↗
PubMed1979

A physical model of nerve axon. II: Action potential and excitation currents. Voltage-clamp studies of chemical driving forces of Na+ and K+ in squid giant axon.

An adsorption model of nerve axon has been extended to account for the origin of membrane currents observed under voltage-clamp conditions. Differing from the Hodgkin-Huxley model, which attributes excitation solely to a change of ionic conductances of the membrane, the present model proposes that a layer of axoplasm attached to the membrane (axon cortex) can undergo conformational changes and hence modulate selectivity for mobile ions. To test the model, a two-step voltage-clamp study was made of the chemical driving forces of Na+ and K+ ions in squid giant axon. The forces were measured by determining the instantaneous current-voltage relation when membrane current is carried by Na+ only or K+ only. The data indicate that the chemical driving force varies as a function of time and does not agree with the Nernst relation during the early phase of excitation. Implications of the observations are discussed.

Action Potentials↗
PubMed1977

Systemic effect of benign and malignant mammary tumors on the spin-lattice relaxation time of water protons in mouse serum.

The spin-lattice relaxation time (T1) for water protons in sera was significantly (P less than 0.001) elevated above that for normal sera in mice bearing benign ductal papilloma and malignant mammary carcinoma. Serum T1 values did not differ significantly in mice with ductal hyperplasia or preneoplastic alveolar nodules. Elevated serum T1's could not be explained on the basis of serum iron levels or serum protein concentrations. This was the first report of a "systemic effect" of serum T1 elevation by a benign tumor.

Animals↗
PubMed1976

The spin-lattice relaxation times of water associated with early post mortem changes in skeletal muscle.

We studied the spin-echo signal of muscle water in a large time domain and found that the motion of the nuclear magnetic moment of tissue water cannot be characterized by a single spin-lattice relaxation time (T1). The relaxation time T1B, which is the T1 characterized by those protons with a slower relaxation rate, is influenced by the early post mortem changes in skeletal muscle. T1B increased with time after the tissue was taken from the animal and reached a maximum at 3 h. However, the weighted average of T1 of all water protons (T1A) did not change throughout the time course of the experiments.

Animals↗
PubMed1976

Nuclear magnetic resonance measurement of skeletal muscle: anisotrophy of the diffusion coefficient of the intracellular water.

The anisotropy of the spin-diffusion coefficient Ds of water protons in skeletal muscle has been studied by pulsed NMR methods. The mid-portion of the tibialis anterior muscle of mature male rats was placed in a special sample holder by means of which the muscle fiber orientation theta relative to the diffusion direction could be varied over the range 0 degrees less than or equal to theta less than or equal to 90 degrees. The value of Ds(theta) was determined for theta = 0 degrees, 45 degrees, and 90 degrees. The measured anisotropy Ds(0)/Ds(90) was 1.39, and the value of Ds(0) was 1.39 X 10(-5) cm2/s. These results are interpreted within the framework of a model calculation in which the diffusion equation is solved for a regular hexagonal network similar to the actin-myosin filament network. The large anisotropy, and the large reduction in the value of Ds measured parallel to the filament axes lead to two major conclusions: (a) interpretations in which the reduction in Ds is ascribed to the effect of geometrical obstructions on the diffusion of "free" water are ruled out; and, (b) there is a large fraction of the cellular water associated with the proteins in such a way that its diffusion coefficient is substantially reduced.

Animals↗
PubMed1975

Nuclear magnetic resonance studies on human breast dysplasias and neoplasms.

The ability of nuclear magnetic resonance (NMR) spectroscopy to distinguish normal, diseased non-neoplastic, and neoplastic human breast tissues was investigated with T1 and T2 relaxation times used. The results indicated that NMR relaxation times could distinguish between the mean values of breast neoplasms and other diseased or normal tissues, with P values less than 0.001. Given a single sample, the probability of classifying it nonneoplastic or carcinoma could be accomplished with 85% confidence. For human breast tissues, the relaxation time T2 may be more discriminating that T1. These results support the view that the use of NMR spectroscopy in cancer detection may be of significant value and warrants considerable more interest and effort to determine the beneficial applications and limits of this technology.

Adenocarcinoma↗
PubMed1974

Nuclear magnetic resonance transverse relaxation times of water protons in skeletal muscle.

The observation of the spin-echo decay in a long time domain has revealed that there exist at least three different fractions of non- (or slowly) exchanging water in the rat gastrocnemius muscle. These fractions of water are characterized with different nuclear magnetic resonance (NMR) relaxation times and are identified with the different parts of tissue water. The water associated with the macromolecules was found to be approximately 8% of the total tissue water and not to exchange rapidly with the rest of the intracellular water. The transverse relaxation time (T(2)) of the myoplasm is 45 ms which is roughly a 40-fold reduction from that of a dilute electrolyte solution. This fraction of water accounts for 82% of the tissue water. The reduced relaxation time is shown neither to be caused by fast exchange between the hydration and myoplasmic water nor by the diffusion of water across the local magnetic field gradients which arise from the heterogeneity in the sample. About 10% of the tissue water was resolved to be associated with the extracellular space, the relaxation time of which is approximately four times that of the myoplasm. Mathematical treatments of the proposed mechanisms which may be responsible for the reduction of tissue water relaxation times are given in this paper. The results of our study are consistent with the notion that the structure and/or motions of all or part of the cellular water are affected by the macromolecular interface and this causes a change in the NMR relaxation rates.

Animals↗