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H G Hempling

Publications and source records attributed to H G Hempling.

At least 19 recordsLinked to original sources
PubMed1993

Analyzing an electrogenic cotransporter.

A model for the sodium-dependent accumulation of glutamate by synaptosomes has been presented which fits the data of Wheeler and his coworkers and supports their hypothesis of an electrogenic cotransporter. Since their hypothesis was based on experimental data on the operation of the cotransporter on the outer membrane, the model was expanded to predict events when the cotransporter was operating on both sides of the membrane. The model predicts that the accumulation of glutamate is sensitive to the synaptosomal sodium and emphasizes the importance of the sodium/potassium pump to maintain this value. A model which uses only an electrogenic form of the cotransporter on the external membrane and a neutral form on the inside of the membrane predicts too much or too little accumulation of glutamate at different membrane potentials. A model which uses an electrogenic cotransporter on the external membrane and a concentration-dependent sodium glutamate leak would require a significant increase in the permeability of sodium glutamate when the membrane depolarizes. Only the operation of all four mentioned mechanisms will fit experimental data at two different external sodium concentrations and over the range of membrane potentials measured experimentally.

Amino Acid Transport System X-AG↗
PubMed1991

Osmotic properties of cells: a computer laboratory.

A computer laboratory has been designed to teach the osmotic properties of cells. One program, CELL.BA, is for the teacher to enter values for the volume of cell water and osmotically inactive material, the concentration of impermeant solute in the cell, and the permeability of the plasma membrane to water and a nonelectrolyte. When the program is protected, students use it as a cell with unknown osmotic properties. They run experiments on the computer with different concentrations of impermeant or permeant solutes or combinations of the two. Changes in cell volume or solute concentration are collected as data and analyzed with the program, PERMEABILITY LAB.BA. This program provides a parameter list, and students try to fit the data that are graphed on the screen by choosing values for the unknown cell parameters and generating model curves. Programs are written for the Macintosh computer.

Animals↗
PubMed1989

Analysis of ion channels by modeling the osmotic effects of weak acids and bases.

This paper describes computer programs which may be used to identify and analyze cation and anion channels. Weak acids are used to increase intracellular proton concentrations and by so doing to promote the exchange of osmotically active cations with protons. The time course of cation exchange is readily identified from the changes in cell volume which accompany the net changes in osmotically active cations. Weak bases are used to identify and analyze hydroxyl/anion exchange by a comparable strategy. The model was able to produce data that agreed with experimental data in the literature with an accuracy equal to experimental error. One program, called PROPIONATE, uses the weak acid, propionic acid, to identify cation channels such as the sodium-proton exchanger or the calcium-dependent, potassium channel. A second program, called BASE, is more general because either a weak acid such as propionic acid or a weak base such as ammonia may be used individually or together. When experimental data are available, the programs may be used to calculate permeability coefficients for ion channels and the capacity of intracellular buffers. The programs may be used also in the design of experiments. Initial values may be assigned to intracellular and extracellular electrolyte and proton concentrations. Values for intracellular buffer capacity and channel permeabilities may be chosen. The program will then generate changes in ions, cell volume, and intracellular pH when either a weak acid, a weak base or combination of the two is added to the external medium.

Ammonium Chloride↗
PubMed1989

Mathematical model of edema in the isolated rabbit lung perfused with oleic acid.

The development of edema by the isolated, perfused rabbit lung in response to oleic acid was analyzed with the equations of Kedem and Katchalsky (Biochim. Biophys. Acta 27: 229-246, 1958). A perfused cylinder and annulus surround was chosen as a model. Isolated lungs, perfused with an isosmotic solution containing dextran as an oncotic agent, received a bolus injection of oleic acid into the pulmonary artery, resulting in marked edema without a rise in mean pulmonary arterial pressure. Hydrostatic pressure was kept constant and in the model was converted to its equivalent concentration of osmotically active impermeant solute, with a reflection coefficient (sigma) of 1. Fluid changes could be analyzed with three principal components as follows: the capillary permeability to solute (Pk), the hydraulic coefficient (Lp), and sigma. The equations were solved using Euler's method for integration, and the values for the three coefficients were adjusted to fit the data. The analysis indicated that the edema measured experimentally could be simulated by a progressive increase in Lp at constant or increasing values of Pk and decreasing values for sigma but not after selective increases in Pk and/or decreases in sigma alone. The analysis suggests that an expanding hydraulic conductivity may be the rate-limiting factor in oleic acid-induced pulmonary edema in the isolated, perfused rabbit lung.

Animals↗
PubMed1985

The effects of dimethyl sulfoxide on the osmotic properties of a rat megakaryocytopoietic cell line.

Dimethyl sulfoxide (DMSO) at 0.6 M alters the osmotic state of intracellular water in a line of rat megakaryocytopoietic cells. The response is a function of temperature. Maximal structuring of water occurs at 24.7 degrees C, while disorganization occurs at 30 and 37 degrees C. Little effect occurs at 3 and at 18 degrees C. Parallel measurements of membrane permeability to water indicate that DMSO inhibits the osmotic exit of water at all temperatures. Maximal inhibition occurs at 24.7 degrees C, the same temperature at which maximal organization of water occurs. These findings emphasize the possible role which water may play in explaining the diverse functions of DMSO as cryogenic substance, promoter of cell fusion, and stimulator of cell differentiation.

Animals↗
PubMed1984

Permeability of cultured megakaryocytopoietic cells of the rat to dimethyl sulfoxide.

The permeability of the membrane of the rat megakaryocytopoietic cell to dimethyl sulfoxide was measured to assess its availability to the intracellular compartment. The method used was osmotic, and measured the initial loss of cell water followed by a reswelling to isotonic volume when cells were placed in culture media containing 0.6 M DMSO. Values for the hydraulic coefficient, Lp, the permeability of the membrane to DMSO, wRT , and the reflection coefficient were calculated from the equations of Kedem and Katchalsky . The average value at 25 degrees C for Lp was 0.46 micron min-1 atm1 ; wRT was 9.3 micron min-1, and the reflection coefficient was 0.65. At these cell volumes, 50% equilibration occurred in 5 sec. Cells equilibrated in 0.6 M DMSO increased their volume of osmotically inactive water. Coupled with this phenomenon of stabilization of water was a reduction in the hydraulic coefficient by 50%. These findings are discussed in the context of current hypotheses about cellular viability during freezing and thawing in the presence and absence of cryoprotectants.

Animals↗
PubMed1981

State of water and electrolytes in mammalian cells during maturation and differentiation.

The state of water and electrolytes was examined 1) in the rat erythroblastic leukemic cell, as a model of a maturing erythrocyte; 2) in the mouse Ehrlich ascites tumor cell during the cell cycle as a model of the uninhibited proliferating cell; and 3) in a clonal population of proliferating and differentiating precursor cells cultured from the bone marrow of the rat. Methods used were phenomenological and included assessments of the volumes of osmotically active water, content of K+, Na+, and Cl-, volumes of distribution for Na+, urea, and ethylene glycol, and the thermodynamics of transport of water and solutes into and out of the cell. The erythroblastic leukemic cell provided evidence for compartments of osmotically active and inactive water and solute. The synchronized ascites tumor cell indicated that these compartments varied during the cell cycle. Membrane function as defined by its permeability to water also varied during the cell cycle. When proliferating cells matured, changes in membrane permeability to water and to nonelectrolytes also correlated with successive stages of differentiation.

Animals↗
PubMed1980

Osmotic properties of a proliferating and differentiating line of cells from the bone marrow of the rat.

The effects of cellular differentiation on the osmotic properties of a proliferating line of bone marrow cells has been investigated. This population proliferated and differentiated into distinct maturation phases which have been separated quantitatively by velocity sedimentation at 1g in a Ficoll gradient. Certain osmotic characteristics were evaluated. The volume of osmotically active water increased linearly with maturation. The osmotically inactive volume was variable during proliferation and maturation. Several correlations that concerned the exosmotic movement of water were noted, as follows: 1) membrane permeability to water increased with an increase in the diameter of the nucleus, 2) the ratio of osmotically active water to mean corpuscular volume increased with an increase in the diameter of the nucleus, 3) membrane permeability to water increased with an increase in the osmotically active water normalized to the mean cell volume, and 4) the heat of activation associated with the permeability of the membrane to water increased during maturation and varied inversely with the ratio b/MCV. These results were used to assess the effects of cellular maturation on membrane function and the state of water in a maturing cell population. The permeability data suggest that charged groups on membrane proteins and phospholipids can vary the state of water in the membrane from a thermodynamically mobile state to an "ice-like" state. These unusual properties may be a direct result of a dynamic and functional relationship between cellular water and active biological macromolecules.

Animals↗
PubMed1980

Osmotic properties of differentiating bone marrow precursor cells: membrane permeability to non-electrolytes.

Membrane permeability to the non-electrolyte probes urea and thiourea was measured in a population of differentiating bone marrow precursor cells (Cicoria and Hempling, '80). The phenomenologic equations of Kedem and Katchalsky ('58) were applied. The population of cells, which can be separated by velocity sedimentation, was examined over the maturation range of 400 to 1,000 cubic micra. Several membrane properties were observed: 1) Solute permeability (omega RT) increased linearly as the cell volume increased, while the reflection coefficients (sigma) remained constant. 2) Membrane permeability to urea was significantly greater than to thiourea; however, their respective sigmas did not differ significantly. Solute permeability was independent of sigma at 22 degrees C. 3) In the two maturation phases observed, omega RT varied directly with the volume of osmotically active water. 4) The permeability to urea and to thiourea has provided information on the characteristics of the pathways used for water and non-electrolytes, as well as a description of the phenomenologic membrane events accompanying cellular maturation.

Animals↗
PubMed1980

Electrolyte and non-electrolyte distribution in the Ehrlich ascites tumor cells during the cell cycle.

In a previous study, evidence was presented for changes in the state of water and osmotically active solutes during the cell cycle. Total water was constant at 82% (w/w), while the fraction of water that was osmotically active decreased from a maximum during S to a minimum at mitosis. Total Na+, K+, and C1- in milliequivalents per liter of cell water remained constant. Therefore, electrolytes are sequestered in the osmotically inactive water. Evidence is now presented that Na+ exists primarily as one compartment, with a second, slower compartment appearing during S and disappearing during G2. Na+ is completely exchangeable during the entire cell cycle. The distribution of other penetrating solutes was also investigated. When placed in hyperosmotic ethylene glycol solutions, cells first shrink, then swell to their original volumes. 14C-ethylene glycol distributes in 89% of cell water throughout the cell cycle. However, 14C-urea distributes in anywhere from 86-100% of the cell water, depending on the stage in the cell cycle. Both solutes are at chemical equilibrium in water in which they are distributed, but they differ in their effects on cell volume. The final volume at which cells equilibrate in urea varies with the concentration of urea in the environment and with time into the cell cycle. Results suggest a loss of osmotically active particles or decreased osmotic activity of urea.

Animals↗
PubMed1978

Osmotic properties of Ehrlich ascites tumor cells during the cell cycle.

Ehrlich ascites tumor cells were grown and maintained in continuous spinner culture. The population of dividing cells was synchronized by a double thymidine block technique. Cell cycle phases were determined graphically by plotting mitotic index, cell number, and DNA synthesis against time. Changes in the osmotic properties of Ehrlich ascites tumor cells during the cell cycle are described. Permeability to water is highest at the initiation of S and progressively decreases to its lowest value just after mitosis. Heats of activation for water permeability vary during the cell cycle, ranging from 9-14 kcal/mole. Results may imply changes in the state of water in the membrane during the cycle. The volume of osmotically active cell water is highest during S and early G2 and decreases during the mitotic phase, as cells undergo division. Total water content remains stable at 82% (w/w) during the cycle. Total concentration of the three major ions (Na, K, Cl), expressed as mEq/liter total cell volume, does not change. The fraction of total cell water which is osmotically active (Ponder's R) decreased gradually from 0.75 at S to about 0.56 following mitosis. Findings suggest that a fraction of the total water within the cell exists in a "bound" form and is, therefore, incapable of being shifted under the driving force of osmotic pressure. This fraction of bound water increases during the cell cycle. Possible alterations in membrane fluidity and the state of water in the cell are discussed.

Animals↗
PubMed1977

Osmotic properties of human lymphocyte.

The osmotic properties of human lymphocytes isolated from 15 ml of venous blood were examined. Measurements of the permeability of the membrane to water under an osmotic gradient were also made. The Boyle-Van't Hoff relation held very well for the human lymphocyte when the cells were shrunken in hyperosmotic media to concentrations twice isosmotic. The volume of osmotically inactive material or "b" value averaged 32% of the mean corpuscular volume. These values were independent of temperature. Ponder's R ranged between 0.8 and 0.9. The average value for Lp, the hydralic coefficient was 0.46 mu/min atm +/- 0.02 (S.E.M.) at 25 degrees C. No significant effect of age, sex, or race was noted. The effect of temperature between 10 degrees C and 37 degrees C was measured and heats of activation between 11.1 and 17.4 kcal/mole were calculated with a mean of 14.1 kcal/mole +/- 1.6 (S.E.M.). Concanavalin A at 10 microgram/1.5 X 10(6) lymphocytes produced blastogenesis of 25% or more of the lymphocytes without clumping, agglutination, or toxicity. The mean corpuscular volume increased by 21% after 72 hours due to an increase in the "b" value which increased by 80%. The volume of free water remained constant. Histograms of the distribution of cell volumes showed that volume changes were uniform throughout the population with no evidence of agglutination of clumping. The significance of these results is discussed in the context of membrane fluidity and the state of intracellular water.

Cell Membrane Permeability↗
PubMed1975

Maturation of membrane function: the permeability of the rat erythroblastic leukemic cell to water and to non-electrolytes.

The erythroblastic leukemia produced in Long-Evans rats by the administration of 7, 8, 12 trimethylbenz (a) anthracene has been used as a model of the most immature form of the erythrocyte series. In conjunction with studies of the maturation of several other membrane functions, the permeability of this cell to water and to certain definitive non-electrolytes was measured with osmotic methods. The hydraulic conductivity, L-p was 6.2 micro (minute)-1, (atm)-1 at 25 degrees C, quite high and characteristic of mature erythrocytes, but different from values of 0.65 for immature myeloid cells. The effect of temperature provided an energy of activation of 4.4 kCal/mole, also typical of mature mammalian erythrocytes but again different from 13 to 18 kCal/mole for immature myeloid cells. Urea was compared to thiourea. The permeability coefficient for urea was 76.7 micra (minute)-1 plus or minus 13.8 (S. E.); the value for thiourea was 1.55 micra (minute)-1 plus or minus 0.18 (S. E.). Phloretin at 0.25 mM inhibited urea permeability by 90% with 50% inhibition occurring at 0.05 mM. Inhibition was reversible. Permeability to the glycols was also compatible with mature erythrocytes. We infer from these findings that the structure which underlies these basic, passive membrane functions is laid down early and persists after loss of nucleus and subsequent maturation.

Animals↗