PubMed Health⌕ Search

Biomedical subjects

B Chu

Publications and source records attributed to B Chu.

84 records · Page 5Linked to original sources
PubMed1985

Short-term fluctuations and long-term trends in anchorage-independent multiplication among cryopreserved subpopulations of a spontaneously transformed Balb/3T3 clone.

A spontaneously transformed clone of Balb/3T3 cells which produced primitive pleomorphic sarcomas in nude mice was maintained in serial passage without cryopreservation. It was also cryopreserved at an early passage and thawed out at four successive intervals. The capacity of these 5 subpopulations to form colonies while suspended in agar (CFEag) was assayed repeatedly over a period of almost 3 years. The initial CFEag and the subsequent pattern of change were unique for each of the subpopulations. When later passages of the nonfrozen subpopulation were cryopreserved and then thawed, there was only a slight change in CFEag and colony size in agar. There were differences in multiplication rates of 3 of the subpopulations on plastic surfaces in the same rank order as their CFEag, but the differences were smaller. Short-term fluctuations in CFEag, however, were not paralleled by changes in multiplication rate on plastic. The nonfrozen subpopulation assumed the appearance of nontransformed fibroblasts when crowded for several days on plastic, and these "normalized" cells had a greatly reduced CFEag when assayed in agar. Neither the change in appearance nor the decrease in CFEag with prolonged incubation of crowded cells occurred with one of the cryopreserved subpopulations which had the same CFEag and growth rate on plastic as the nonfrozen subpopulation under optimal conditions. The evidence favors an epigenetic rather than a genetic origin of the variations in appearance and behavior of the subpopulations.

Animals↗
PubMed1984

Dynamic laser light scattering of papain-treated thick filaments from limulus striated muscle in suspension.

Using quasielastic light scattering we have previously shown an increase in high frequency internal motion of isolated thick filament upon activation. This we have attributed to cross-bridge motion. Here we show that after cleavage of the S1 moiety of myosin from isolated filaments with papain, calcium ions no longer activate the isolated filaments to produce high-frequency motions.

Animals↗
PubMed1983

Quasi-elastic light scattering of suspensions of Limulus thick myofilaments in relaxed (long) activated and rerelaxed (short) states.

Photoelectron count autocorrelation function of light scattered by Limulus thick myofilament suspensions was measured as a function of scattering angle in the relaxed, activated and rerelaxed states. By using the cumulants method of data analysis, the average linewidth over large ranges of KL (up to 120), has been calculated with K and L being, respectively, the magnitude of the momentum transfer vector and the length of the myofilament. We have observed a dramatic increase in the average linewidth denoting the presence of additional high frequency components for the myofilament suspension on the activated state. By confirming our results on the size of the myofilaments from electron micrographs, we are able to attribute the high frequency (kHz) components to the "correlated" cross-bridge motions, representing, to our knowledge, the first direct experimental evidence of such movements in isolated thick myofilament suspensions.

Animals↗
PubMed1980

Thymidine as a chemotherapeutic agent: pharmacologic, cytokinetic, and biochemical studies in a patient with T-cell acute lymphocytic leukemia.

Biochemical studies suggested that leukemia T-cells have low levels of TTP-catabolizing enzyme activity and are uniquely sensitive to thymidine (dThd). A child with T-cell acute lymphocytic leukemia (ALL), whose peripheral blood lymphoblasts manifested very low TTP catabolic capacity, was treated with 75 g dThd/m2/day by constant iv infusion for two courses of 5 and 8 days. The dThd caused an initial accumulation of peripheral blood blasts in S-phase at the expense of cells in G1, followed by a rapid reversal of this pattern consistent with a block in late G1 and/or early S. Concurrently, a prompt reduction of blasts was found in the peripheral blood. However, dThd treatment neither decreased the number of lymphoblasts in the cerebrospinal fluid (CSF) nor cleared the marrow. No major toxicity was observed, but the effect of dThd on normal marrow elements could not be evaluated in this patient. Blood concentrations of dThd were 1.4-3.0 mM, and concentrations of thymine were in the same range; beta half-life for dThd was 48 minutes. Steady-state CSF dThd was 9% of the simultaneous serum level. Clearance measurements demonstrated that catabolism of dThd was saturated and that renal clearance was a major determinant of total body clearance during high-dose dThd infusion. A good correlation was found between biochemical and cytokinetic parameters and response to dThd for the peripheral blood lymphoblasts. However, dThd did not produce a useful remission in this case of T-cell ALL.

Antineoplastic Agents↗
PubMed1978

Reversible regulation by magnesium of chick embryo fibroblast proliferation.

The rate of 3H-thymidine incorporation and of cell proliferation in chick embryo fibroblast cultures are reduced coordinately when the [Mg2+] of the external medium is reduced below the physiological concentration of about 0.8 mM. These effects of moderately reduced [Mg2+] and the accompanying change in appearance of the cells, resemble the effects produced by lowering the [serum] of the medium. Cells subjected to severe Mg2+ deprivation, especially at low [Ca2+], die and detach from the culture dish. Cells kept at a reduced rate of proliferation for three days by moderate Mg2+ deprivation are quickly restored to rapid proliferation upon restoration of the normal [Mg2+] of the medium. The rate of proliferation of the chick embryo cells is reduced markedly by lowering [Ca2+] about 100-fold, but unlike the case of Mg2+-deprivation this can occur without significant effect on the rate of 3H-thymidine incorporation. More severe Ca2+ deprivation, which does lower the rate of 3H-thymidine incorporation, produces retraction of cells from one another and from the dish, and results in a distinctly abnormal, rounded appearance. The results lend weight to the thesis that free [Mg2+] plays a central role within the cell in the coordinate control of metabolism and growth. They also suggest that the effects produced by varying [Ca2+] in the medium are caused by changes at the external surface of the cell.

Blood↗
PubMedDate not supplied

Study of large DNA fragments in agarose gels by transient electric birefringence.

The pulsed-field gel electrophoresis (PFG) is a newly developing technique used in the fractionation of large DNA fragments. Advances in PFG demand a better understanding in the corresponding mechanisms of DNA dynamics in the gel network. Detailed experiments are needed to verify and to extend existing theoretical predictions as well as to find optimum conditions for efficient separation of large DNA fragments. In the present study, deformation of large DNA fragments (40-70 kilobase pairs) imbedded in agarose gels were investigated by using the transient electric birefringence (TEB) technique under both singular polarity and bipolarity electric pulses at low applied electric field strengths (E less than or equal to 5 V/cm). The steady-state optical retardation (delta s) of DNA molecules is linearly proportional to E2. At a given E, the amplitude of optical retardation [delta(t)] increases monotonically with the pulse width (PW) and then reaches a plateau value [delta(t = 0) = delta s] where t = 0 denotes the time when the applied field is turned off or reversed. The field-free decay time (tau-a few minutes) is several orders of magnitudes slower than that from previous TEB observations using high electric field strengths (E-kV/cm) and short pulse widths (PW-ms). The degree of deformation (stretching and orientation) and the time of restoration to the equilibrium conformation of overall DNA chains have been related to delta and tau. In field inversion measurements, exponentially rising and linearly falling of birefringence signals in the presence of forward/inverse applied fields were observed. The rising and falling of birefringence signals were reproducible under a sequence of alternating pulses. Comparison of our results with literature findings and discussions with theories are presented.

DNA↗