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K Bhaumik

Publications and source records attributed to K Bhaumik.

11 recordsLinked to original sources
PubMed2005

A possible mechanism of zero-crossing detection using the concept of the extended classical receptive field of retinal ganglion cells.

The extended classical receptive field (ECRF) of retinal ganglion cells has been modelled as a combination of three zero-mean Gaussians at three different scales that has been shown to be equivalent to a Biharmonic or Bi-Laplacian of Gaussian filter. It has also been shown that the ECRF can be approximated by a combination of Laplacian of Gaussian (LoG) and the Dirac-delta function. Zero-crossings detected with this operator are more informative than those detected by the traditional filters like LoG or Difference of Gaussians (DoG) that had been devised using the classical receptive field of the ganglion cells. We have also explained that such an additional information processing is not in contradiction with the recent experimental findings on the physiology of retinal ganglion cells.

Animals↗
PubMed1997

On the dynamics of synaptic vesicles: effects on the rate of neurotransmitter release.

Release of transmitter substances during synaptic communication in a biological process of great importance, and it is worthwhile to ascertain the basic molecular events underlying this process. We present a minimal model of synaptic vesicle (SV) dynamics, with which most of the major experimentally observed features of evoked neurotransmitter release can be reproduced. The effect of different parameters on the time course of evoked release as well as the effect of repetitive stimulation on this model system has been examined.

Animals↗
PubMed1994

Fetal hemoglobin synthesis in sickle cell anemia: some molecular considerations.

An ability to maintain high levels of fetal hemoglobin (Hb F) has been associated with the amelioration of the clinical severity of the sickle cell disease (SS). Clinical efforts to increase the Hb F level of the patients have, however, yielded variable therapeutic response. In an attempt to further elucidate the underlying molecular basis, in vitro Hb F synthesis was studied in erythroid progenitor (BFU-E) cells obtained from SS patients and their heterozygous (AS) relatives with varying genetic backgrounds. This allows us to study the Hb F biosynthesis pattern uncomplicated by the influence of the preferential survival of "F cells" in vivo. The Hb F levels and the relative concentrations of its constituent gamma globin chains, G gamma and A gamma, were assayed using the reversed phase HPLC method. A percentage increase in the fetal hemoglobin content was observed in the lysates of the erythroid progenitor cells relative to the circulating peripheral blood erythrocyte values in SS patients and their AS relatives with different beta S haplotypes reflecting the intrinsic capacity of fetal hemoglobin synthesis in these subjects. No such increase was observed in the patient with the Mor haplotype. Furthermore, the Hb F synthesized in the BFU-E colonies was more of the adult type, as evidenced by the decrease in the percent G gamma level relative to the corresponding peripheral blood values of the subjects in all the haplotype groups studied. The Mor haplotype was again an exception, synthesizing fetal hemoglobin more of the fetal type.

Anemia, Sickle Cell↗
PubMed1991

K562 cells: a source for embryonic globin chains.

A combination of DEAE-cellulose chromatography and reversed-phase high-performance liquid chromatography (HPLC) has been used to devise a method for generating large quantities of embryonic as well as fetal globin chains. The identity of these globin chains was further confirmed by their tryptic peptide mapping. This technique could, therefore, provide a reliable source for these polypeptides for both analytical and immunological purposes. Moreover, the study of human hemoglobin switching, particularly embryonic to fetal, has been greatly hampered by the absence of a suitable model. K562 cells, due to their potential for differential induction of embryonic and fetal hemoglobin synthesis, can thus be used for this purpose and the various hemoglobins produced can then be effectively monitored using this method.

Chromatography, DEAE-Cellulose↗
PubMed1991

Evidence for the synthesis of embryonic globin chains in adult erythroid progenitor cells.

Embryonic globin chains were found to be synthesized in vitro by the BFU-E colonies derived from adult sickle cell anemia (SS) patients, their heterozygous relatives as well as a few normal controls. In the absence of sufficient material for conducting direct structural analyses of these peptides, they were confirmed by evaluating the co-migration of the epsilon and zeta-chains with the corresponding structurally characterized globin chains obtained from K562 cell lysates on a reversed phase high performance liquid chromatogram. The presence of zeta-chain was also confirmed using an immunologic procedure. Furthermore, significant 35S-methionine incorporation peak was observed corresponding to the zeta-chain synthesized by the BFU-E-derived colonies implying an active synthesis of this embryonic globin chain in BFU-E cells obtained from hemopoietically adult persons.

Anemia, Sickle Cell↗
PubMed1989

Application of high-performance liquid chromatographic methodology to the analysis of hemoglobins synthesized in erythroid progenitor cells.

High-performance liquid chromatography (HPLC) has been successfully used in the quantitation of the relatively minute amounts of hemoglobin types recovered from in vitro cultures of hemoglobin-synthesizing erythroid progenitor (BFU-E) cells. This reversed-phase HPLC method uses the Vydac C4 column and water-acetonitrile-trifluoroacetic acid as mobile phases; it has been applied to the study of fetal hemoglobin synthesis patterns in ten homozygous sickle cell anemia patients and a similar number of their heterozygous relatives along with a few normal control subjects. A significant increase in the total gamma chain level was observed in the BFU-E lysate samples corresponding to the whole blood lysates of all the patients and their heterozygous relatives, except in one patient with the beta S haplotype Mor. On the other hand, the relative level of the G gamma chains appeared to be decreased in the BFU-E lysate samples of all except the individuals carrying the Mor haplotype, where it is reversed. The method has considerable advantages over other chromatographic and electrophoretic procedures; it is extremely sensitive and allows quantitation of all different globin chains in one single chromatogram.

Adolescent↗
PubMed1989

Hemoglobin synthesis in BFU-E colonies derived from transfused blood in a sickle cell anemia patient.

In an in vitro progenitor cell culture system, a significant amount of normal hemoglobin (Hb A) synthesis was observed in a transfused sickle cell anemia (SS) patient, indicating the contribution of stem cells obtained from the normal donor's blood cells. As this study was done long after the last blood transfusion (greater than 100 days), the survival of the donor's stem cells would indicate their repopulating the recipient's bone marrow. On extending the study to a few other transfused SS patients who had received multiple blood transfusions at frequent intervals, no such synthesis of Hb A was observed. A loss of repopulating ability of the donor's stem cells with frequent transfusions at short intervals is suggested as a possible explanation, with a gradual development of immune response against these cells as a second possibility. The differences in the survival of the donor's stem cells would thus appear to have some reflection on the frequency of blood transfusions required by an individual patient.

Anemia, Sickle Cell↗