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Biomedical subjects

S M Friedman

Publications and source records attributed to S M Friedman.

At least 163 records · Page 9Linked to original sources
PubMed1977

Glass electrode measurement of net Na+ and K+ fluxes in erythrocytes of the spontaneously hypertensive rat.

The exchange of Na+ and K+ in rat red cells at 40% hematocrit incubated in a physiological salt solution containing 1 MM ouabain was monitored with ion-specific glass electrodes. Because this system measures a change in the activity of an ion as a logarithmic function of its preexisting level, delta[K+]o is more accurately measured than delta[Na+]o; within this limitation, the downhill ion movements were close to 1:1 over the temperature span from 37 to 3 degrees C. These transmembrane movements are reasonably well expressed in terms of first-order kinetics and an Arrhenius plot constructed for K+ as the accurate indicator of the exchange yields an activation energy of 12 kcal/mol. A well-defined reversal of the usual direct relation of temperature to exchange rate was observed between 6 and 3 degrees C. The net ion movements were distinctly faster at low temperature in cells from rats with spontaneous hypertension (SHR-Okamoto) than in cells from matched controls (Woodlyn and WKY).

Animals↗
PubMed1976

Increased erythrocyte permeability to Li and Na in the spontaneously hypertensive rat.

Red blood cells incubated in a physiological medium in which Li replaces Na (LiPSS) gain Li in exchange for Na and K. The rate of Li uptake is modestly but significantly increased in the spontaneously hypertensive rat (SHR) at 37 degrees C and at 22 degrees C. The slow rate of Na gain and K loss during cooling at 2 degrees C was about doubled in unmodified whole blood samples from the SHR.

Animals↗
PubMed1976

Surface topography of the Bacillus stearothermophilus ribosome.

The surface topography of the intact 70S ribosomes and free 30S and 50S subunits from Bacillus stearothermophilus strain 2184 was investigated by lactoperoxidase-catalyzed iodination. Two-dimensional polyacrylamide gel electrophoresis was employed to separate ribosomal proteins for analysis of their reactivity. Free 50S subunits incorporated about 18% more 125I than did 50S subunits derived from 70S ribosomes, whereas, free 30S subunits and 30S subunits derived from 70S ribosomes incorporated similar amounts of 125I. Iodinated 70S ribosomes and subunits retained 62-78% of the protein synthesis activity of untreated particles and sedimentation profiles showed no gross conformational changes due to iodination. The proteins most reactive to enzymatic iodination were S4, S7, S10 and Sa of the small subunit and L2, L4, L5/9, L6 and L36 of the large subunit. Proteins S2, S3, S7, S13, Sa, L5/9, L10, L11 and L24/25 were labeled substantially more in the free subunits than in the 70S ribosome. Other proteins, including S5, S9, S12, S15/16, S18 and L36 were more extensively iodinated in the 70S ribosomes than in the free subunits. The locations of tyrosine residues in some homologous ribosomal proteins from B. stearothermophilus and E. coli are compared.

Electrophoresis, Polyacrylamide Gel↗
PubMed1976

Cell permeability, sodium transport, and the hypertensive process in the rat.

The tail artery of the spontaneously hypertensive rat (SHR) (Carworth Farms), excised rapidly and immersed immediately in cold (2 degrees C) Li-substituted physiologic salt solution (LiPSS), continues to exchange cell Na+ and K+ for Li+, this exchange is negligible to the control (Carworth Farms normotensive) CFN). In the incubated artery at 37 degrees C, when the vascular smooth muscle cell is slack, the leakiness of the cell membrane in the SHR is more than offset by increased Na+ pumping activity, so that cell Na+ is subnormal. A high precision technique with ion-specific electrodes was developed to follow the passive downhill and active uphill phases of Na+-K+ exchange in the perfused artery exposed to K+-free physiologic salt solution (K+-free PSS) followed by physiological salt solution (PSS). The exchange was found to be fully reversible and sufficiently equimolar to be definable in terms of movements of K+ alone. The rates of ionic movement across the vascular smooth muscle cell were found to be about 6 times faster for the vessel perfused at low pressure (less than 3 mm Hg) than for the slack incubated artery. The rate of passive downhill movement was significantly accelerated in the mature SHR compared with CFN, and the net active transport activity much enhanced. Similar changes were seen as early as 3 weeks after treatment with DOCA and were pronounced at 8 weeks. It is proposed that conditions favoring a sustained accumulation of Na+ in the vascular smooth muscle cell are countered by an enhanced synthesis of transport protein, of contractile protein, and of paracellular matrix protein which progressively restructure the wall.

Animals↗
PubMed1976

Triggering of human peripheral blood B cells: polyclonal induction and modulation of an in vitro PFC response.

In the present studies we utilized polyclonal activators to analyze the signals required to induce antibody synthesis by subpopulations of human peripheral blood lymphocytes. The in vitro synthesis of antibody directed against sheep erythrocytes was measured by a modification of the Jerne plaque assay. The plaques observed contained central lymphoid cells, could be inhibited by anti-human immunoglobulin, and were strictly dependent on both the addition of complement and viable B lymphocytes actively synthesizing protein. Kinetic analysis showed that the PFC response developed over time during cell culture with peak activity occurring between days 6 and 7. It was found that human peripheral blood B lymphocytes, isolated by Sephadex G-200 anti-Fab column chromatography, were nonspecifically induced by either PWM or soluble products of antigen-activated human T cells to differentiate into PFC. In contrast, unfractionated peripheral blood lymphocytes. Ig- cells isolated from immunoabsorbant columns, and B cells enriched by nylon wool adherence were not triggered to antibody synthesis even in the presence of polyclonal activators. B cells isolated by nylon wool adherence and further fractionated by binding and elution from anti-Fab columns were then readily triggered by PWM to differentiate into PFC. These results suggest that the interaction of human B cells with anti-Fab columns, presumably at the Ig receptor, serves as a signal important in the differentiation events leading to PFC activity. The anti-Fab interaction alone, although critical, was not sufficient to induce the differentiation of precursor cells into PFC since subsequent triggering by antigen-activated T cell supernatants or PWM was required for the development of an optimal PFC response. Additional experimental data demonstrated that the PFC response could be regulated by autologous peripheral Ig- lymphoid cells in vitro. At low concentrations of PWM, Ig- cells consistently augmented the B cell PFC response whereas at high concentrations of PWM, suppression was observed. Depletion of E rosetting cells from the Ig- population eliminated the subset responsible for augmentation but did not eliminate the suppressor cell activity.

Animals↗
PubMed1975

Comparison of net fluxes of Li and Na in vascular smooth muscle.

The rat tail artery enriched by incubation in a lithium-substituted medium loses Li at three distinct rates upon return to a normal medium at 37 degrees C. The first is very rapid with a single exponential rate constant of the order of 1 min-1, while the second and third are considerably slower with rate constants of the order of 3h-1 and 0.6h-1, respectively. Both slow components are cellular since they combine into a single component when active Na transport is inhibited by the absence of external K, by ouabain, or by low temperature. None of these procedures affects the rapid loss of Li from extracellular locations. It follows that cell Li can be measured simply by washing out extracellular Li at 2 degrees C, a procedure which removes only a small definable amount from cells. The influx of Li into cells during incubation in Li-substituted medium follows 1st order kinetics and exchanges 1:1 with cell K after a delay of about 20 min at 37 degrees C. This delay in influx is associated with active Na transport since it is abolished by the absence of external K, by low temperature, and by ouabain. The activation energy required for the influx of Li and of Na in K-free media is consistent, in the main, the passive diffusion through a restricted area although there is a suggestion in the case of Na that an additional mechanism (e.g. carrier) may be involved.

Animals↗
PubMed1975

Cell Na and K in the rat tail artery during the development of hypertension induced by desoxycorticosterone acetate.

An increase in total Na, due in large part to an increase in cell Na, was measured in the freshly excised rat tail artery during the course of DOCA-saline treatment. Since this change was associated with a fall in cell K, was first observed at 2 weeks, coincident with the rise in blood pressure, and was not sustained during subsequent immersion of the artery at zero pressure, it probably reflects the high in vivo intravascular pressure. In the incubated artery, cell Na is significantly reduced early in the course of treatment, while cell K falls late. Thus, Na transport in the artery is under direct attack from the start, but it is suggested that this leads to hypertrophy rather than to vasoconstriction.

Animals↗
PubMed1973

Ambiguity in a polypeptide-synthesizing extract from Saccharomyces cerevisiae.

Environmental factors known to induce ambiguity in bacterial extracts were tested in an in vitro cytoplasmic polypeptide-synthesizing system derived from Saccharomyces cerevisiae. Increasing concentrations of magnesium, spermine, and spermidine resulted in extensive leucine-phenylalanine ambiguity in polyuridylic acid-directed polypeptide synthesis. Kinetic studies showed that spermine-mediated stimulation of leucine incorporation occurred when phenylalanine was being actively incorporated. In addition to leucine, the amino acids isoleucine and serine were incorporated in the presence of added magnesium and spermine. Ambiguity in the presence of a high Mg(2+) concentration was decreased when the pH of the reaction mixture was lowered. Ethanol and neomycin enhanced ambiguity to a small, but significant, extent. Streptomycin and temperature had no effect on ambiguity. Leucine, isoleucine, and serine were not attached to phenylalanine transfer ribonucleic acid (tRNA) when the aminoacylation reaction was performed at increasing Mg(2+) and spermine concentrations. On the other hand, increasing levels of Mg(2+) and spermine stimulated the incorporation of leucine from tRNA into polypeptide during the transfer reaction. The formal similarity between the findings in the yeast and Escherichia coli systems implies the existence of a tRNA-screening site on the yeast ribosome comparable to that suggested for bacteria. A proposal is made as to the manner in which this site may function to produce the ambiguous codon translation observed.

Acylation↗