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Biomedical subjects

Z Ahmed

Publications and source records attributed to Z Ahmed.

At least 109 records · Page 6Linked to original sources
PubMed1987

Determination of the birth date and proliferative state of dissociated cells from fetal rat brain.

The proliferative status and time of origin of dissociated cells from cerebral cortex, basal ganglia, diencephalon, mesencephalon and rhombencephalon of the fetal rat brain have been analyzed. The distributions of cells in different phases of the cell cycle after dissociation and after 7 days in culture have been determined with flow cytofluorometry. Two separate DNA indicators, propidium iodide and Hoechst 33258, have been used. Almost all of the dissociated cells recovered from the 5 brain regions, between embryonic days 15 and 20, are in G1, or growth arrest phase of the cell cycle. In contrast, only about 55% of the liver cells (same fetal age) are in G1, or growth arrest phase. The times of the last in vivo mitoses of the dissociated cells have been determined by maternal injection of [3H]thymidine and autoradiography of cultures. The majority of the cells recovered on embryonic days 16 and 17 from the 5 brain regions appeared to have undergone DNA synthesis within a period of 24 h prior to dissociation. When the fetuses were sacrificed 96 h after the injection, less than 20% of the cells were labelled, and grain density was drastically reduced. Most labelled cells survive in the serum-free culture medium for more than 7 days. Dissociated cultures of synchronized and birth-dated cells from different brain regions of fetal rat should prove particularly useful for the study of cellular development and function.

Animals↗
PubMed1987

DNA glycosylase enzymes induced during chemical adaptation of M. luteus.

Five peaks of DNA glycosylase activity showing a preference for MNNG alkylated DNA have been identified from extracts of adapted M. luteus. They are numerically designated as GI to GV in order of their decreasing molecular weights. The first two of these peaks have been highly purified. GI, is a constitutive heat labile protein, 35% stimulated by the presence of 50 mM NaCl, acts exclusively on 3 MeA residues in alkylated DNA, 60-70% inhibited by the presence of 2 mM free 3MeA and has been designated as 3MeA DNA glycosylase enzyme. GII, which is an inducible protein, is heat stable, 28% inhibited by the presence of 50 mM NaCl, removes 3MeA, 3MeG, 7MeA & 7MeG with different efficiency, and has been designated as 3,7 methylpurine DNA glycosylase enzyme. The rate of release of 3 methylpurines is 30 times that of 7MeG. There is no activity of either enzyme on O2-MeC, O2-MeT, O4-MeT or O6-MeG. The apparent molecular weights of GI and GII proteins are 28 Kd and 22 Kd respectively.

Bacterial Proteins↗
PubMed1987

[Severe pulmonary mycobacteriosis caused by Mycobacterium simiae].

We report a case of pulmonary mycobacterial infection due to Mycobacterium simiae followed between 1968 and 1985 and leading to unilateral pulmonary destruction. Formal bacteriological proof was obtained by culturing from the pneumonectomy specimen. None of the usual features of immunosuppression were found. This is the first case suffering from this germ described in this part of the world.

Female↗
PubMed1986

Expression of membrane currents in rat diencephalic neurons in serum-free culture.

The whole-cell gigaseal voltage clamp technique has been used to investigate the timing of expression and type of voltage-dependent ionic currents in dissociated primary cultures of fetal rat (E17) diencephalic neurons grown in a serum-free defined medium. The expression of membrane currents varied among cells at any particular time in culture. Despite this variability, certain characteristics of the appearance of ionic currents emerge from this study. These are: (i) the earliest appearing membrane current is a voltage-dependent outward current carried by K+. In some cells, it is the classical delayed rectifier current, whereas in others it is the transient outward current (IA). (ii) The earliest appearing inward current is carried by Na+. In some cells the channels are first expressed in the neurites and then in or near the cell body. The early neuritic Na+ channels are blocked by cobalt or cadmium as well as by tetrodotoxin (TTX). In others, the early Na+ channels appear in or near the cell body and are only blocked by TTX. (iii) With additional time in culture, a majority of cells exhibit a Ca2+ current at the time of Na+ channel appearance in or near the cell body as well as a transient Ca2+-dependent outward current. The Ca2+ current is only a small fraction of the total inward current. These inward currents show the classical pharmacologic profile. The complex pattern of expression of ionic current may reflect multiple populations of neurons with different developmental sequences resulting from differences in cell age and lineage.

Action Potentials↗
PubMed1985

Isolation and characterization of Streptomyces venezuelae mutants blocked in chloramphenicol biosynthesis.

Twelve Streptomyces venezuelae mutants blocked in chloramphenicol biosynthesis were isolated. Two of these (Cm1-1 and Cm1-12) were apparently blocked in the conversion of chorismic acid to p-aminophenylalanine and three (Cm1-4, Cm1-5 and Cm1-8) accumulated p-aminophenylalanine and may have been blocked in the hydroxylation reaction that converted this intermediate to p-aminophenylserine. One mutant (Cm1-2) accumulated D-threo-1-p-nitrophenyl-2-propionamido-1,3-propanediol and D-threo-1-p-nitrophenyl-2-isobutyramido-1,3-propanediol, indicating that chlorination of the alpha-N-acyl group of chloramphenicol was blocked. The remaining six strains did not excrete any detectable chloramphenicol pathway intermediates.

Chloramphenicol↗
PubMed1984

Adaptive response of Micrococcus luteus to alkylating chemicals.

Wild type M. luteus cells have been adapted by a step-wise treatment with sub-lethal concentrations of MNNG. The adapted cells exhibit 5.7 fold increased resistance to the killing effects of the mutagen and a simultaneous efficient removal of various base modifications present in cellular DNA. A protein extract prepared from adapted cells contains inducible repair functions which can reduce 80-90% of the alkylated DNA content of 06-MeG is effected by a transmethylase and there is no concomitant release of the modified base. However, N-3 MeG is released as a free modified base through the action of a DNA glycosylase. The release of N-3 MeA is unaffected by the induction treatment whereas that of N-7 methylpurine is slightly improved in the adapted cells.

Alkylating Agents↗
PubMed1984

Diffusion of ions and indicator dyes in neural cytoplasm.

The dispersion of dye molecules and small cations injected from a point source in the cytoplasm of molluscan neurons has been measured photometrically and compared with dispersion in aqueous solution. The diffusion of phenol red and arsenazo III was at least a factor of five slower in the cytoplasm than in saline. Movement of both dyes was slowed by about the same factor in a given cell. The dispersion rate of arsenazo III was not significantly affected by preloading the cytoplasm to dye concentrations up to 0.5 mM. Calcium and barium dispersion was measured in neurons and saline droplets preloaded with arsenazo III, while phenol red absorbance changes were used to follow the dispersion of injected protons. Ba2+ and H+ moved very slowly in the cytoplasm compared to aqueous solution. Ca2+ movement in all probability underwent a similar retardation in the neurons but high-affinity buffering of the cytoplasm severely restricted the spread of detectable amounts of this ion away from the injection site.

Animals↗
PubMed1983

Properties of neurons from dissociated fetal rat brain in serum-free culture.

Because of the unknown constituents and varying composition of serum, its presence in media used in cell culture unavoidably compromises attempts to study cellular mechanisms of growth and differentiation. To overcome this, we have devised a serum-free, chemically defined medium which maintains primary cultures of fetal rat brain cells for more than 6 weeks. This medium allows expression of characteristic properties of neurons and prevents overgrowth of non-neuronal elements without use of antimitotic agents. Cells prepared and plated without exposure to serum attach in less than 20 min to poly-D-lysine substratum and begin to extend processes within 1 hr. After 2 days in culture, process-bearing cells can be divided into those with characteristic neuronal morphology, including long processes which generally branch at a distance from the perikaryon, and those having the appearance of glial cells with many short, thin processes which branch frequently near the cell body. The remaining non-neuronal cells are large and flat with few or no processes. The presence of neurons and astroglia was demonstrated by immunofluorescence detection of bound tetanus toxin as a neuron-specific surface marker, and glial fibrillary acidic protein as an astroglial marker. By the 3rd day in culture, many cells of neuronal morphology were able to generate action potentials in response to electrical stimulation. The ionic composition of the inward current changes from Ca2+ to predominantly Na+ by about 10 days in culture. The presence of synaptic vesicles and myelin was demonstrated by electron microscopy. The ability of dissociated cells from mammalian brain to grow in defined medium without serum and acquire selected properties of mature cells in vivo demonstrates the potential of this culture system for neurobiological studies at the cellular level.

Action Potentials↗
PubMed1981

Cirrhosis of liver.

Clinical analysis of 293 cases of cirrhosis from two moderate sized hospitals in the city of Dacca has been presented. Maximum number of cases were in the age group over 40 with 150 (51.2%) males and 19 (5.8%) females. Significant past history included viral hepatitis (21.5%), kala-azar (11.6%) and malaria (10.24%). History of alcoholism was present only in 16 (5.5%) cases. Weakness (84.3%), weight loss (72%) and anorexia (39.3%) constituted the most common symptoms. Ascites (45%), haematemesis (11.6%) and melaena (28.7%) were the next common symptoms. Hepatosplenomegaly was found in about one-third of the cases. Testicular atrophy was recorded in 41.63% cases whereas gynaecomastia was relatively less common (5.5%). Scanty body hair and white nails were present in almost equal number of cases (14.7% and 18%). The cases presented here are those with overt manifestation. Nevertheless, the clinical features are not materially different from those reported by other authors. In the absence of alcoholism, viral hepatitis is presumably the most important aetiological factor in our cases and the clinical features compare favourably with non-alcoholic cirrhosis of the western writers. Cryptogenic cirrhosis has been considered to be most common type constituting 43.7% of our cases.

Adult↗
PubMed1980

Stoichiometry and apparent dissociation constant of the calcium-arsenazo III reaction under physiological conditions.

In vitro and in situ tests have been run to characterize the reaction of the mettalochromic indicator, arsenazo III, with calcium. Job plots as well as plots of indicator absorbance vs. [Ca2+] at different indicator concentrations show a 1:1 reaction stoichiometry. Equilibrium analysis and analysis using Adair's equation are also consistent with 1:1 complexes being formed and give estimates of 34 and 45 muM for the apparent dissociation constant. In situ tests were carried out using giant neurons from Archidoris monteryensis, a marine gastropod mollusc. Dye absorbance changes were measured during voltage clamp pulses which produced a fixed calcium influx. The dependence of absorbance change on total dye concentration is consistent with the formation of a 1:1 complex of Ca with ArIII if measurements are made during the initial period of the loading pulse, less than 300 ms, although the apparent dependency changes with longer delay in measurements from the onset of the pulse.

Animals↗
PubMed1980

Intracellular pH changes induced by calcium influx during electrical activity in molluscan neurons.

Simultaneous measurements of electrical activity and light absorbance have been made on nerve cell bodies from Archidoris monteryensis injected with indicator dyes. pH indicators, phenol red and bromocresol purple, and arsenazo III, which under normal conditions is primarily a calcium indicator have been employed. Voltage clamp pulses which induced calcium influx caused an absorbance decrease of the pH dyes indicating an internal acidification. The onset of the pH drop lagged the onset of Ca2+ influx by 200-400 ms, and pH continued to decrease for several seconds after pulse termination which shut off Ca2+ influx. Trains of action potentials also produced an internal pH decrease. Recovery of the pH change required periods greater than 10 min. The magnitude of the pH change was largely unaffected by external pH in the range 6.8-8.4. The voltage dependence of the internal p/ change was similar to the voltage dependence of calcium influx determined by arsenazo III, and removal of calcium from the bathing saline eliminated the pH signal. In neurons injected with EGTA (1-5 mM), the activity-induced internal Ca2+ changes were reduced or eliminated, but the internal pH drop was increased severalfold in magnitude. After the injection of EGTA, voltage clamp pulses produced a decrease in arsenazo III absorbance instead of the normal increase. Under these conditions the dye was responding primarily to changes in internal pH. Injection of H+ caused a rise in internal free calcium. The pH buffering capacity of the neurons was measured using three different techniques: H+ injection, depressing intrinsic pH changes with a pH buffer, and a method employing the EGTA-calcium reaction. The first two methods gave similar measurements: 4-9 meq/unit pH per liter for pleural ganglion cells and 13-26 meq/unit pH per liter for pedal ganglion cells. The EGTA method gave significantly higher values (20-60 meq/unit pH per liter) and showed no difference between pleural and pedal neurons.

Action Potentials↗
PubMed1979

Measurement of calcium influx under voltage clamp in molluscan neurones using the metallochromic dye arsenazo III.

1. The metallochromic indicator dye, arsenazo III, was injected into somata of molluscan neurones from Archidoris monteryensis. Membrane current and dye absorbance change were simultaneously monitored under voltage clamp. 2. Absorbance measured at 660 nm increased during positive-going voltage steps large enough to activate membrane conductances. In situ idifference spectra were qualitatively similar to dye, dye-calcium difference spectra recorded in vitro. The absorbance change was abolished by either a thorough removal of external calcium or internal chelation of calcium by EGTA. It was concluded that the absorbance increase primarily reflected changing internal calcium concentration and that the calcium entered from the outside. 3. Dye absorbance increased in a nearly linear fashion during voltage clamp pulses of 100--300 msec duration. This is in qualitative agreement with electrical stuidies which demonstrated only fractional inactivation of calcium conductance during such periods. Plots of absorbance change vs. Vm peaked at +30 to +40 mV and fell off sharply until approximately +70 mV where the slope became less steep. A null or reversal of the absorbance change was generally observed aroung +110 mV. Evidence is presented that calcium influx was in some cases sufficient to cause sizeable changes in its equilibrium potential. 4. During multisecond voltage clamps the slope of the absorbance change showed a large decline. Where barium substituted for calcium as the influx species in identical clamps, the absorbance at 660 nm also increased but in a much more linear fashion. Except for a slight effect on the initial few pulses, the absorbance signal did not recover after a period of barium influx. These results suggest that part of the slope decline might result from processes related to calcium uptake and not to membrane conductance decrease. 5. Dye absorbance changes during normal and TEA action potentials were measured. Comparison of these changes with voltage clamp records indicated that calcium influx during a spike was capable of raising concentration by roughly 2 X 10(-7) M if the cell were considered to be a uniform sphere with no buffering capacity. Calcium influx during action potentials was increased dramatically by TEA, primarily as a result of a prolonged plateau phase. The existence and duration of the plateau was controlled mainly by potassium conductance systems, however. There was no evidence found for facilitation of the calcium conductance. 6. Following a moderate influx of calcium it required 20--60 sec, depending on the neurone, for the dye absorbance to return to base line (at 9 degrees C). The recovery time course showed a marked difference when examined at different wavelengths. For lambda = 660 nm there was an initial period in which the absorbance decreased rapidly, followed by a slower phase which generally carried the absorbance below the initial (prepulse) value...

Action Potentials↗
PubMed1979

Hypertension in Secretariate population of Bangladesh.

A total of 8,172 persons constituting 98.6% of the total Secretariate Population of Bangladesh were screened for elevated blood pressure. One thousand and ninety cases (13.3%) showed diastolic blood pressure of 90 mmHg or above. Those with diastolic blood pressure of 95 or above constituted 3.7% of the population. More than two-thirds of the latter group (71.6%) remained undetected indicating that vast majority of our hypertensive population remains undiagnosed and untreated. It is recommended that the misconception regarding symptomatic hypertenson should be removed by adequate emphasis on the preventive value of the control of hypertension on cardiovascular and cerebrovascular complication. A plea has also been made for a large-scale survey to determine the extent of the problem in Bangladesh.

Adolescent↗