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Biomedical subjects

Z Ahmed

Publications and source records attributed to Z Ahmed.

At least 91 records · Page 5Linked to original sources
PubMed1992

Alterations of plasma membrane fatty acid composition modify the kinetics of Na+ current in cultured rat diencephalic neurons.

Properties of inward Na+ currents (INa) were examined in dissociated diencephalic neurons whose plasma membrane fatty acid composition had been altered. These neurons were grown in a defined medium supplemented with essential fatty acids (EFA) of either the w3 class (linolenic acid, 18:3w3) or the w6 class (linoleic acid, 18:2w6), which resulted in a two-fold increase in the plasma membrane phospholipid polyunsaturated fatty acid (PUFA) concentration. The properties of the inward INa of these neurons were compared with those of control neurons grown in the absence of any supplemented fatty acids. The INa of neurons supplemented with a non-essential fatty acid (NFA) of w9 class (oleic acid, 18:1w9) was also examined. Several properties have been modified to different degrees. The ratio of the amplitudes between the fast and the slow decay components as well as the time constant of the fast decay component changed consistently and reversibly with the membrane phospholipid PUFA composition. The current-voltage relationships, channel selectivity, rates of inactivation and recovery from inactivation did not change. Other parameters, such as time-to-peak and steady-state inactivation curves, have changed in EFA- and NFA-supplemented cultures and did not reverse completely. These findings demonstrate that the kinetics of INa can be modified by fatty acid supplementation. These effects can be correlated, in part, with alterations in plasma membrane phospholipid fatty acid composition.

Animals↗
PubMed1991

Cholinergic stimulation produces oscillations of cytosolic Ca2+ in a secretory epithelial cell line, T84.

The effects of carbamylcholine (carbachol) on intracellular Ca2+ concentration ([Ca2+]c) of T84 cells were examined using the fluorescent Ca2+ indicator fura-2 and microfluorometric techniques. In single isolated cells, carbachol (100 microM) caused a rapid increase in [Ca2+]c of 184 +/- 15 nM (SE, n = 44) from a resting value of 56 +/- 7 nM. This initial transient was followed by a series of oscillations in 68% of the cells. Atropine (10 microM) blocked this response. Removal of bath Ca2+ did not inhibit the rise in [Ca2+]c or oscillations, but the response duration was shortened in 47% of the cells. The amplitude and latency of the initial Ca2+ rise, frequency of oscillations, and number of responding cells varied with the agonist concentration. We have previously shown that carbachol induces an oscillating K+ conductance in T84 cells [D. Devor, S. Simasko, and M. Duffey. Am. J. Physiol. 258 (Cell Physiol. 27): C318-C326, 1990]. Simultaneous measurement of membrane K+ current and fura-2 fluorescence in the same cell demonstrated a correlation between the rise in [Ca2+]c and increase in K+ current. These results show that a rise in [Ca2+]c and oscillations is likely to underlie the membrane K+ current responses to carbachol in T84 cells. Responses from a single cell within a subconfluent monolayer were different from those of isolated cells. In cells of a monolayer the initial [Ca2+]c rise (111 +/- 8 nM; n = 41) was followed by a decline to a stable plateau, and oscillations were not seen. Removal of bath Ca2+ both reduced the initial transient and eliminated the plateau phase of the response. These results suggest that cell-to-cell contact or differentiation during monolayer formation influences the Ca2+ handling mechanisms of T84 cells.

Animals↗
PubMed1991

Characterization of sodium current in developing rat diencephalic neurons in serum-free culture.

1. Dissociated, synchronized (G1 phase of cell cycle), and birth-dated fetal rat diencephalic neurons were grown in a serum-free defined medium. The gigaseal whole-cell voltage-clamp technique was used to measure the inward Na+ currents (INa) from morphologically identified bipolar neurons. The earliest expressed somatic INa has been characterized and compared with that present at a later date. 2. The identity of the INa was established on the basis of its reversal potential and reversible blockade by tetrodotoxin (TTX). Close agreement between the measured reversal potentials (68.5 +/- 1.3 and 38.3 +/- 2.4 mV, mean +/- SE) and calculated Nernst equilibrium potentials (64.6 and 34.7 mV) at two different bath Na+ concentrations (120 and 35 mM, respectively) suggests that the channels are highly selective for Na+. 3. The peak INa density increased from 47.7 +/- 2.9 pA/pF in younger neurons (5-6 days in culture) to 93.9 +/- 6.4 pA/pF in older neurons (12-13 days in culture). The activation voltage and the voltage for peak current were also shifted by 10 mV in the hyperpolarizing direction, from -30 and +10 mV in younger neurons to -40 and 0 mV in older neurons, respectively. However, the reversal potential did not change (69.2 +/- 2.3 and 68.5 +/- 1.3 mV in younger and older neurons, respectively). 4. In older neurons the steady-state inactivation parameters (V1/2, the voltage at which inactivation was 50% of maximum, and kh, the voltage at which there is an e-fold change in inactivation) were significantly altered. V1/2 was shifted from -41.5 +/- 2.3 to -48.8 +/- 1.8 mV, and kh was increased from 6.2 +/- 0.5 to 8.9 +/- 0.4 mV. However, the time course of activation and the rates of inactivation and recovery from inactivation were unchanged. 5. In both groups, the INa decays were best described by a sum of two exponentials. The corresponding time constants were voltage dependent. Also, the amplitudes of the two components were differentially affected by membrane potential and niflumic acid. 6. The extrapolated amplitudes of both the fast and the slow components of INa were larger in older neurons, but the ratio of the amplitudes of the two components did not change with age. The voltage dependencies of the time constants of both components were altered. 7. We conclude that INa in fetal rat diencephalic neurons grown in a defined medium with only essential nutrients undergoes in vitro changes in current density and in some, but not all, kinetic parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

A characterization of glycinergic receptors present in cultured rat medullary neurons.

1. Whole-cell current responses to bath application of glycine, beta-alanine, and taurine were studied in medullary neurons cultured from embryonic rats. 2. Two current components were seen in the responses to bath application of agonist, one component that desensitized and another that did not. 3. The two current components have different dose-response characteristics, with the nondesensitizing component being activated more effectively at lower concentrations than the desensitizing component and also reaching its peak at lower concentrations. The agonist concentrations producing half-maximal responses are 26 +/- 4 (SE, n = 6) and 69 +/- 17 (n = 7) microM for the nondesensitizing and desensitizing components, respectively, for glycine; 54 +/- 7 (n = 9) and 127 +/- 37 (n = 7) microM for beta-alanine; and 153 +/- 24 (n = 9) 443 +/- 99 (n = 3) microM for taurine. Thus, for each component, the order of potency is glycine greater than beta-alanine greater than taurine. 4. When total responses to glycine, beta-alanine, and taurine are compared in the same cells, taurine and beta-alanine are less potent agonists than glycine, with relative potencies of 1:0.4:0.1 for glycine-beta-alanine-taurine. 5. The desensitizing component is more sensitive to strychnine than the nondesensitizing one. The strychnine concentrations that block 50% of the response to a control dose of agonist are 15 and 500 nM for the desensitizing and nondesensitizing components, respectively, for glycine; 60 nM and 1 microM for beta-alanine; and 18 and 500 nM for taurine. 6. The complete occlusion between the responses to glycine and beta-alanine or glycine and taurine suggests that these agonists activate the same receptors. 7. The two current components may be manifestations of one receptor population with complicated kinetics or two independent receptor populations.

Animals↗
PubMed1991

Effect of transfusions.

1. The transfusion effect, which was apparent in 1981, disappeared in 1988, and reversed itself in 1990. In other words, for the first time, transfused patients have started to have lower graft survival rates than nontransfused patients. 2. The proportion of transfused to nontransfused patients has decreased from a ratio of 10:1 in 1981 down to 1:1 in 1990. 3. The transfusion effect in related donors has also disappeared in recent data. 4. Data revealed that HLA-A,B, and DR mismatching had no effect between 1988 and 1990. 5. A small transfusion effect continues to be seen in young recipients. 6. In earlier data, the transfusion effect was most marked in Blacks and Hispanics, but the reverse trend is now shown for these races. White recipients had exactly the same survival rates with and without transfusions. 7. Sensitization occurred more often with transfused patients who had a tendency toward slightly lower graft survival. This was true in males, females, and pregnant females. 8. Recipients who waited on dialysis for more than 2 years had slightly lower graft survival and data showed they had received more transfusions. 9. The loss of the transfusion effect occurred at both large and small centers. The centers with 1-year graft survival under 70% tended to have a transfusion effect, whereas those above 70% had either better or worse results with transfusions.

Actuarial Analysis↗
PubMed1990

Glutamate stimulates release of Ca2+ from internal stores in astroglia.

We report here that, in the absence of external Ca2+, glutamate produces a transient increase in intracellular Ca2+ [( Ca2+]i) in cultured spinal cord astrocytes, by mobilizing internal Ca2+ stores. [Ca2+]i was measured with Fura-2 using the ratiometric method. Astrocytes were identified by immunostaining for glial fibrillary acidic protein. Glutamate and quisqualate consistently caused a transient increase in [Ca2+]i, with both the response amplitude and latency being graded functions of agonist concentration. Some cells produced multiple transients. N-Methyl-D-aspartate, kainate and aspartate were ineffective. We conclude that the quisqualate subtype of glutamate receptors mediates release of Ca2+ from internal stores in mammalian astrocytes.

Animals↗
PubMed1990

Developmental changes in the regulation of glycine-activated Cl- channels of cultured rat medullary neurons.

Glycine-activated currents in 1- to 11-day-old rat medullary neurons were studied using patch clamp techniques. Glycine produced neither repeatable whole-cell current responses nor single-channel activity in the cell-attached mode until cells were in culture for a week or more. However, Cl- channels were present at the early stages because glycine-activated channels were seen in excised, inside-out patches. Furthermore, for cells less than a week in culture, 10 patches which did not exhibit glycine-activated Cl- channels in the cell-attached mode did upon excision. Consequently, the activation properties of these Cl- channels undergo a developmental change in that some cellular factor(s) presumably prevents the Cl- channels from opening in the intact cell during the initial stages in culture.

Animals↗
PubMed1990

Introduction of percutaneous arteriovenous femoral shunt: a new access for continuous arteriovenous hemofiltration.

In most critically ill unstable patients, continuous arteriovenous hemofiltration (CAVH) and continuous arteriovenous hemofiltration with dialysis (CAVHD) offer significant advantages over dialysis and ultrafiltration. Improvements in CAVH methodology have occurred since its introduction, but an ideal vascular access has yet to be designed. Scribner shunts may result in loss of a future access site, while femoral artery and vein catheterization render the patient immobilized. We have developed a percutaneous external arteriovenous femoral shunt to overcome this difficulty. The catheter consists of two single-lumen flexible polyurethane catheters with a subcutaneous Dacron cuff. A percutaneous Seldinger technique is used with a peel-away sheath to insert one catheter in the artery and one in the vein. To minimize infection and ensure durability, a 10-cm tunnel is created so that the exit of the catheters on the upper thigh is away from the groin. Like the Scribner shunt, a connecting tube is used between the catheters to maintain the patency when the shunt is not in use. Our experience with this technique is limited to seven treatments in seven patients (five CAVH, two CAVHD). Good blood flow (average, 80 mL/min), ultrafiltration rate (7 mL/min), and biochemical studies demonstrated the efficiency of the access. The average treatment was 10 days and patients were allowed to do moderate movement without resulting thrombosis or infection of the access. The major advantages of this new and efficient access for CAVH and CAVHD include simple introduction by a nephrologist, lack of potential serious complications, avoidance of sacrifice of major vessels, early ambulation and movement without compromising function, and a design for prolonged usage.

Catheterization, Central Venous↗
PubMed1990

Manipulation of plasma membrane fatty acid composition of fetal rat brain cells grown in a serum-free defined medium.

Modifications of plasma membrane acyl-linked phospholipid fatty acid composition were produced by supplementing the culture medium with essential fatty acids. The plasma membrane fraction was purified by Percoll gradient centrifugation from dissociated fetal rat brain cells grown in a serum-free culture medium. Both the concentration dependence and the time course of the modifications were examined. Supplementation of the medium with essential polyunsaturated fatty acid, linolenic acid (18:3 omega 3) or linoleic acid (18:2 omega 6), produced incorporation of the elongated and desaturated products of omega 3 or omega 6 class, respectively, i.e., the incorporation was class specific. Within each class, the most unsaturated and elongated members, i.e., terminal members, were preferentially incorporated until they reached a maximum concentration within 6-7 days. At higher concentrations of supplemented fatty acids, additional class specific incorporation in plasma membrane was produced by an increase in the concentration of intermediate members. At the same time, the concentration of monounsaturated fatty acids declined and that of saturated fatty acids remained unchanged. The modifications in fatty acid composition were reversible, with the time course similar to that of incorporation. The total plasma membrane phospholipid and sterol contents did not change with alterations of fatty acid composition, but did change with time in culture. This preparation should prove useful for investigating the role of polyunsaturated fatty acids in brain cell functions, including neuronal excitability.

Animals↗
PubMed1990

Health sciences libraries and information services in Bangladesh.

Basic problems relating to the status of health sciences libraries and information centers in Bangladesh are highlighted and discussed; strategies for improving the country's health sciences information services are suggested. A survey of libraries is reported, the country's national science and technology information policy is defined, and recommendations for action are proposed.

Bangladesh↗
PubMed1990

Total and coronary heart disease mortality in relation to major risk factors--Quebec cardiovascular study.

The relationships of blood pressure, smoking, serum cholesterol and education levels on total and coronary artery disease (CAD) mortality were evaluated in 4576 Quebec men aged 35 to 64 years, free from overt CAD at entry and followed for 12 years. From January 1974 to January 1986, there were 417 deaths, 131 due to CAD. A progressive increase in total and CAD mortality was observed from quintile 3 to 5 for both systolic and diastolic blood pressure. In comparison to quintile 1, the adjusted relative risks of quintiles 4 and 5 for systolic blood pressure were significantly elevated (2 P less than 0.01), being 1.5 and 2.0 for total mortality, and 2.6 and 3.5 for CAD mortality, respectively. The relative risks of quintiles 4 and 5 for diastolic blood pressure were also significantly elevated (2 P less than 0.04), being 1.5 and 1.6 for total mortality and 1.9 and 2.7 for CAD mortality, respectively. In comparison to those who never smoked, the relative risks of smoking one to 20, and 21 and more cigarettes per day, were 2.1 (2 P less than 0.003) and 3.1 (2 P less than 0.0001) for overall mortality, and 2.2 (2 P less than 0.08) and 3.5 (2 P less than 0.002) for CAD mortality. Men who had discontinued smoking at least one year before the study, had a relative risk not different from those who had never smoked. Serum cholesterol and education levels were not significantly associated with total or CAD mortality.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

[The incidence of atypical pulmonary mycobacterium infections in Reunion before the era of acquired immunodeficiency syndrome (AIDS)].

The authors analyzed cases of pulmonary non-tuberculous mycobacterial infection observed in the Reunion Island between 1979 and 1986, before any reported case of AIDS in the Island. Isolation of non tuberculous mycobacteria from bronchopulmonary specimens was estimated at 21.4% among all positive cultures (n = 971). The analysis of clinical and biological data from 791 different patients with a positive culture concluded to the responsibility of a non tuberculous mycobacteria in 117 (14.8%); among these 117, only 10 (8.5%) were considered as pathogen. Species repartition, antituberculous drug sensitivity and clinical out come are discussed.

Adult↗
PubMed1989

Characteristics of glycine-activated conductances in cultured medullary neurons from embryonic rat.

Characteristics of glycine-activated currents in 10- to 20-day-old neurons were studied using the gigaseal whole-cell technique. Glycine activated a Cl- conductance that was blocked by strychnine acting as a mixed inhibitor, effecting both Imax and Kd. Glycine receptors with at least two different sensitivities to strychnine were found, based on the apparent inhibition constants (Ki). These two Ki values were associated with different Hill coefficients for the glycine responses. Cs+ activated the same receptor and also activated a relatively nonselective cation conductance.

Animals↗
PubMed1988

Expression of membrane currents in rat neocortical neurons in serum-free culture. I. Inward currents.

The gigaseal whole-cell voltage clamp technique has been used to investigate the timing of expression and properties of voltage-dependent inward currents in cultured neocortical pyramidal-shaped neurons. The dissociated primary cultures of synchronized (same cell cycle), growth arrested (G1-phase) and birth-dated neurons from fetal rat (E18) were maintained in a serum-free medium. The earliest inward current is expressed within 24 h. This current is carried by Na+ and the channels are located in distal neurites at discrete sites. The Na+ channels near the cell body are expressed after 5 days in culture, at which time the neuritic Na+ current persists. The magnitude of the current near the soma increases with age of the neuron. The Na+ current is blocked by both tetrodotoxin (TTX) and nitrendipine. The sensitivity to nitrendipine changes with age of the culture. The results suggest that Na channels expressed early during neuronal development have some structural component common also to Ca2+ channels.

Animals↗
PubMed1988

Expression of membrane currents in rat neocortical neurons in serum-free culture. II. Outward currents.

The timing of expression and properties of outward membrane currents in cultured neocortical pyramidal-shaped neurons have been investigated using the gigaseal whole-cell voltage clamp and single-channel recording techniques. Dissociated primary cultures of synchronized (same cell cycle), growth arrested (G1 phase) and birth-dated cells from fetal rat (E18) were maintained in a serum-free medium. The earliest appearing membrane current in the soma is a voltage-dependent outward current carried by K+. The current consists of two components, one rapidly rising component, resembling those associated with the transient outward current (IA) and the other similar to the delayed rectifier current (IK). The ratio between the peak IA and IK was about 0.3 at all membrane voltages. The magnitude of both IA and IK increased with time in culture but the ratio remained unchanged. Direct measurements of unitary currents showed the presence of two voltage-activated outward conductances, 32 pS and 120 pS. The small conductance channel was sparse. The large conductance channel is K+-selective and was sensitive to both voltage and internal Ca2+.

Animals↗
PubMed1988

Calcium regulation by and buffer capacity of molluscan neurons during calcium transients.

The properties of Ca-regulation and -buffering of physiological levels of Ca-transients were examined in the soma of Archidoris monteryensis neurons. The rate of recovery from a Ca-transient was examined with two experimental protocols; in one the pulse duration was kept constant and its amplitude was varied, and in the other the duration was varied while the amplitude was kept constant. These experiments revealed that the recovery from a Ca-transient was approximately a first order process and the apparent first order rate constant was dependent on the duration of Ca-influx. The calcium buffer capacity of the cytoplasm was determined by an indirect method which utilised measured amounts of intracellular EGTA to reduce transient changes in free calcium. An equation for the cytoplasmic buffer capacity was derived on the assumption that the capacities of exogenous and endogenous Ca buffers summate linearly. The resting cytoplasmic Ca buffer capacity was 45.2 microM/delta pCa, when it was assumed that the incoming Ca diffuses a distance of 10 microns into the cytoplasm. For a diffusion distance of 5 microns it was 34.5 microM/delta pCa. In both cases, the buffer capacity increased with an increase in the size of Ca transient.

Animals↗