Biomedical subjects

K E Hunter

Publications and source records attributed to K E Hunter.

At least 19 recordsLinked to original sources

PubMed1999

(15)O water positron emission tomography in language localization: a study comparing positron emission tomography visual and computerized region of interest analysis with the Wada test.

We compared (15)O water positron emission tomography (PET) auditory and visual confrontational naming activation with an intracarotid amobarbital (Amytal) injection procedure (IAP) for language lateralization in 12 patients with intractable epilepsy. PET scans were evaluated by three raters experienced in functional imaging as well as by a region of interest (ROI) approach. Compared with IAP, raters' positive predictive value for language lateralization ranged from 88 to 91%. ROI analysis had a positive predictive value of 80%. Six patients had surgery; 1 with right-sided IAP language dominance but left-sided PET activation had dysphasia for 6 months after left temporal lobectomy.

Adolescent↗

PubMed1999

Infant sleep position: A telephone survey of inner-city parents of color.

OBJECTIVE: To assess what positions parents were placing their infants to sleep and their opinion about sleep positioning. DESIGN: A prospective telephone survey of parents of 2-month-old infants with repeated measures at 4 months that began during the second wave of the Back to Sleep campaign in 1994. PARTICIPANTS: African-American, Hispanic, Asian, and American Indian parents from inner cities in the north central United States. RESULTS: Preference for prone positioning existed at both 2 and 4 months (over 40%). Twenty-four percent of parents disagreed with the recommendations of the American Academy of Pediatrics regarding supine or lateral positioning. CONCLUSIONS: Although prone sleep positioning has decreased over the past 5 years, many inner-city parents of color prefer this over supine. The Back to Sleep campaign appears effective in changing attitudes and medical personnel appear influential in promoting risk reductions associated with sudden infant death syndrome. More efforts are clearly needed to convince parents who disagree with and resist recommendations.sleep, infants, SIDS, African-Americans, Back to Sleep (campaign).

Ethnicity↗

PubMed1995

Radial glial cell transformation to astrocytes is bidirectional: regulation by a diffusible factor in embryonic forebrain.

During development of mammalian cerebral cortex, two classes of glial cells are thought to underlie the establishment of cell patterning. In the embryonic period, migration of young neurons is supported by a system of radial glial cells spanning the thickness of the cortical wall. In the neonatal period, neuronal function is assisted by the physiological support of a second class of astroglial cell, the astrocyte. Here, we show that expression of embryonic radial glial identity requires extrinsic soluble signals present in embryonic forebrain. Moreover, astrocytes reexpress features of radial glia in vitro in the presence of the embryonic cortical signals and in vivo after transplantation into embryonic neocortex. These findings suggest that the transformation of radial glia cells into astrocytes is regulated by availability of inducing signals rather than by changes in cell potential.

Animals↗

PubMed1993

Transforming growth factor-betas inhibit mitogen-stimulated proliferation of astrocytes.

We have studied the influence of three members of the transforming growth factor-beta (TGF-beta) family of multifunctional growth factors on the proliferation of cultured astrocytes isolated from newborn mouse cerebral cortex. Although TGF-beta s 1, 2, and 3 cause only a small reduction in the low level of astrocyte proliferation occurring in chemically defined medium, they each inhibit the effects of five astrocyte mitogens (bFGF, EGF, PDGF, IL-1 alpha, and IL-2). Inhibition is observed when astrocytes are exposed to mitogen and TGF-beta at the same time and when they are exposed to TGF-beta prior to, and separately from, mitogen. This latter effect appears to be due to the binding of TGF-beta s to astrocyte-secreted extracellular matrix. These findings raise the possibility that TGF-beta may co-operate with other growth factors to control astrocyte proliferation in vivo.

Animals↗

PubMed1990

Quantitative contribution of factors regulating rat colonic crypt epithelium: role of parenteral and enteral feeding, caloric intake, dietary cellulose level and the colon carcinogen DMH.

To elucidate the role and quantitative contribution of several exogenous factors which may regulate colon crypt mitotic activity, proliferative zone height (PZH) and crypt height, groups of rats were subjected to various feeding regimens both with and without treatment with the colon carcinogen, 1,2-dimethylhydrazine (DMH). The rats were divided into two major groups and one group was given eight weekly injections of DMH base at 9.5 mg kg-1 body weight. Throughout this period and for two additional weeks the rats were isocalorically fed either a defined nutritionally complete diet with different levels of dietary cellulose or they were parenterally (i.v.) fed a nutritionally complete liquid formula with different caloric levels. The rats were then injected with colchicine 3 h prior to sacrifice to arrest and to collect dividing cells at metaphase. The results of multiple regression analysis of all data were interpreted to indicate that parenteral feeding caused dramatic suppression of the colon crypt height (CH) and of the number of metaphase figures per crypt (MC). Increased cellulose intake stimulated CH but suppressed MC. The CH was also stimulated by DMH. CH was positively correlated to PZH and MC. The MC was suppressed by cellulose intake and negatively correlated to PZH but was positively correlated to CH. The PZH was positively correlated to CH. These findings were related to the role of luminal food, functional workload, kcal intake and treatment with DMH on the measured colon crypt parameters. A quantitative assessment of factors that regulate the measured colonic crypt parameters was accomplished.

1,2-Dimethylhydrazine↗

PubMed1990

Evidence that a major portion of cellular potassium is "bound".

In this report we briefly review recent evidence which shows that a substantial proportion of intracellular K+ is "bound" or perturbed from the physicochemical properties expected in dilute aqueous solutions. In addition, we present evidence from electron probe x-ray microanalysis of thin cryosections of cells which indicates that the binding of K+ to anionic groups either carboxyl groups (HCO2) on proteins or to phosphate groups in creatine phosphate (CrP), in adenosine triphosphate, (ATP), in protein and in nucleic acids, are the main determinants of the maintenance of (as differentiated from the generated of) the well known intra- to extracellular K+ concentration difference. The collective evidence suggests that much of cellular K+ is reduced in its mobility and in its chemical activity due to association with negative charge groups (e.g. carboxyl and phosphates). This fact forces abandonment of the misleading assumption that the majority of intracellular K+ and other inorganic ions are as free as would be expected under ideal solution conditions. This realization should have far reaching consequences toward understanding transmembrane movement of water and solutes in cells.

Animals↗

PubMed1989

Effect of dietary cellulose on cell proliferation and progression of 1,2-dimethylhydrazine-induced colon carcinogenesis in rats.

The effects of different levels of dietary cellulose on colonic crypt mitotic activity and colon carcinogenesis were studied in 190 male Sprague-Dawley rats. Rats were divided into groups and fed a basal fiber-free diet supplemented with either 0, 5, or 15% pure cellulose (w/w), for periods of 10 weeks (initiation stage) or 32 weeks (promotional stage). Half of the rats in each group were given weekly s.c. injections of 9.5 mg 1,2-dimethylhydrazine (the base) (DMH) for 8 weeks. Some of the rats were killed at 10 weeks while most were killed 22 weeks later. In some groups the dietary cellulose level was changed to a different level at 10 weeks. Food intake and body weight data showed that the rats within each experiment were isocalorically fed. There was a direct correlation between crypt height and the percentage of cellulose in the diet. Addition of 5 or 15% dietary cellulose during the initiation stage of carcinogenesis resulted in a significant increase in crypt height. Increasing dietary cellulose after the initiation stage (0 to 5% and 5 to 15%) or maintaining a high dietary cellulose level throughout both the initiation and promotional stages (15%) resulted in a significant increase in crypt height. A DMH-induced increase in mitotic activity that was observed during the initiation stage was no longer evident after the 22-week promotional stage. The significant DMH-induced increases in proliferative zone height and crypt height that were initially observed during the initiation stage were also observed after the 22-week promotional stage. These data indicate that the initial DMH-induced increases observed in proliferative zone height and crypt height are irreversible. Addition of 5 or 15% cellulose was found to suppress DMH-enhanced mitotic activity in the crypts of the descending colon during the initiation stage of carcinogenesis. This finding was correlated with a significantly lower incidence of adenocarcinomas in rats maintained on 5 or 15% cellulose throughout both the initiation and promotional stages.

1,2-Dimethylhydrazine↗

PubMed1989

Suppression of a a carcinogen (1,2-dimethylhydrazine dihydrochloride)-induced increase in mitotic activity in the colonic crypts of rats by addition of dietary cellulose.

Serial injections of the colon carcinogen, 1,2-dimethylhydrazine (DMH), have been reported to increase the proliferative activity in the colonic crypts preceding development of tumors. Can addition of purified cellulose to a fiber-free AIN-76 rat diet be used to suppress this increase in proliferative activity? To answer this question rats were divided into two groups, and one group was given eight weekly injections of the DMH base at 9.5 mg/kg of body weight. Throughout this period and for 2 additional wk the rats were isocalorically fed a defined nutritionally complete diet both with and without different dietary levels of cellulose (0, 5, and 15%). The rats were given injections of colchicine 3 h prior to sacrifice to arrest and to collect dividing cells at metaphase. Analysis of variance was performed on various morphometric parameters obtained from histological sections of midaxial crypts from the descending colon. Our results confirm that DMH induced a significant increase in the mitotic activity as measured by the number of metaphase figures per crypt. The presence of dietary cellulose did cause a significant suppression of the DMH-induced increase in the crypt mitotic activity.

1,2-Dimethylhydrazine↗

PubMed1988

Role of plasma membrane and of cytomatrix in maintenance of intracellular to extracellular ion gradients in chicken erythrocytes.

Ultrastructural observations in combination with electron probe X-ray microanalysis on detergent (Brij 58) permeabilized (disruption of the plasma membrane) nucleated chicken erythrocytes support the view that a large fraction of cytoplasmic and nuclear K+ is not freely diffusible and that adsorption of K+ on detergent released mobilizable proteins exists within the cell. The data also suggest that the detergent proteins are normally immobilized by a detergent-resistant cytoskeleton so that they are not immediately free to diffuse from the cell for several minutes after detergent disruption of the plasma membrane.

Animals↗

PubMed1988

Fluctuation in the intracellular concentration of Na+ and Cl- but not of K+ or Mg2+ at mitosis of the first cell cycle in fertilized sea urchin eggs.

This report concerns changes in the cytoplasmic concentration of Na+, Cl-, K+ and Mg2+ during the first cell cycle and into the second cell cycle of fertilized sea urchin eggs of Lytechinus variegatus. The results of electron probe x-ray microanalysis showed a significant equimolar decrease in Na+ and Cl- at the first cell division which was followed by a significant increase early in the second cell cycle. Neither K+ nor Mg2+ showed such significant changes. The loss of a large fraction of the Na+ ions from the egg at metaphase was not accompanied by a significant egg volume change. The observed pattern of ionic change was related to several previously reported chemical and metabolic changes at cell division in sea urchin eggs.

Animals↗

PubMed1988

Quench cooled ice crystal imprint size: a micro-method for study of macromolecular hydration.

Quench cooling (rate greater than 4000 degrees C/sec) of biological specimens limits growth of ice crystals by processes different from slow cooling methods. Quench cooling in liquid propane cooled in liquid nitrogen induced ice crystal segregation compartments, as imaged by scanning transmission electron micrographs of freeze-dried cryosections of tissues and protein solutions. The observed imprints of ice crystals were relatively small and roughly spherical. The size of these ice crystal imprints increased with distance from the specimen/quenchant surface. Beyond a depth of 150 microns the size of the imprints was constant but differed among subcellular compartments. The size of the imprints was found to be dependent on: water content, extent of hydration water and the degree of protein aggregation. Determination of extent of hydration water and degree of protein aggregation in protein solutions by measurements on the size of ice crystal imprints yields data in agreement with macroscopic methods. Thus ice crystal imprints give information about the interactions of macromolecules and water at a subcellular level of resolution.

Animals↗

PubMed1987

The influence of macromolecular polymerization of spin-lattice relaxation of aqueous solutions.

The docking or polymerization of globular proteins is demonstrated to cause changes in proton NMR spin-lattice (T1) relaxation times. Studies on solutions of lysozyme, bovine serum albumin, actin, and tubulin are used to demonstrate that two mechanisms account for the observed changes in T1. Polymerization displaces the hydration water sheath surrounding globular proteins in solution that causes an increase in T1. Polymerization also slows the average tumbling rate of the proteins, which typically causes a contrary decrease in T1. The crystallization reaction of lysozyme in sodium chloride solution further demonstrates that the "effective" molecular weight can either decrease or increase T1 depending on how much the protein is slowed. The displacement of hydration water increases T1 because it speeds up the mean motional state of water in the solution. Macromolecular docking typically decreases T1 because it slows the mean motional state of the solute molecules. Cross-relaxation between the proteins and bound water provides the mechanism that allows macromolecular motion to influence the relaxation rate of the solvent. Fast chemical exchange between bound, structured, and bulk water accounts for monoexponential spin-lattice relaxation. Thus the spin-lattice relaxation rate of water in protein solutions is a complex reflection of the motional properties of all the molecules present containing proton magnetic dipoles. It is expected, as a result, that the characteristic relaxation times of tissues will reflect the influence of polymerization changes related to cellular activities.

Actins↗

PubMed1987

Effect of exercise on riboflavin status of rats.

The effect of exercise on the riboflavin status of male rats was studied after 6 or 8 wk of treadmill running. Sedentary and exercised rats were pair fed diets marginal in riboflavin (2.0 or 2.5 mg/kg), and their tissue riboflavin concentrations and erythrocyte glutathione reductase activity coefficients (EGRAC) were compared. The rats exercised for 8 wk had similar body weights but significantly greater weights for heart, gastrocnemius and soleus muscles, less epididymal fat and more total muscle nitrogen and riboflavin than their sedentary controls. Similar changes were evident after 6 wk of exercise, but some were not statistically significant. The EGRAC values of both exercised and sedentary rats responded to changes in dietary riboflavin but were not different from each other. The specific activity of mitochondrial acyl-CoA dehydrogenase (per milligram protein) of the soleus muscle was unaffected by exercise; however, when expressed per gram of tissue or per muscle, the activities in exercised rats were 25% (P less than 0.05) and 60% (P less than 0.01) higher, respectively, than in sedentary rats. On the basis of the riboflavin-dependent parameters measured in this study, exercise did not increase the dietary riboflavin requirement of growing rats but did increase total riboflavin retention in gastrocnemius and soleus muscles.

Acyl-CoA Dehydrogenases↗

PubMed1987

The locations and amounts of endogenous ions and elements in the cap and elongating zone of horizontally oriented roots of Zea mays L.: an electron-probe EDS study.

We used quantitative electron-probe energy-dispersive x-ray microanalysis to localize endogenous Na, Cl, K, P, S, Mg and Ca in cryofixed and freeze-dried cryosections of the cap (i.e. the putative site of graviperception) and elongating zone (i.e. site of gravicurvature) of horizontally oriented roots of Zea mays. Ca, Na, Cl, K and Mg accumulate along the lower side of caps of horizontally oriented roots. The most dramatic asymmetries of these ions occur in the apoplast, especially the mucilage. We could not detect any significant differences in the concentrations of these ions in the central cytoplasm of columella cells along the upper and lower sides of caps of horizontally-oriented roots. However, the increased amounts of Na, Cl, K and Mg in the longitudinal walls of columella cells along the lower side of the cap suggest that these ions may move down through the columella tissue of horizontally-oriented roots. Ca also accumulates (largely in the mucilage) along the lower side of the elongating zone of horizontally-oriented roots, while Na, P, Cl and K tend to accumulate along the upper side of the elongating zone. Of these ions, only K increases in concentration in the cytoplasm and longitudinal walls of cortical cells in the upper vs lower sides of the elongating zone. These results indicate that (1) gravity-induced asymmetries of ions differ significantly in the cap and elongating zone of graviresponding roots, (2) Ca accumulates along the lower side of the cap and elongating zone of graviresponding roots, (3) increased growth of the upper side of the elongating zone of horizontally-oriented roots correlates positively with increased amounts of K in the cytoplasm and longitudinal walls of cortical cells, and (4) the apoplast (especially the mucilage) may be an important component of the pathway via which ions move in graviresponding rots of Zea mays. These results are discussed relative to mechanisms for graviperception and gravicurvature of roots.

Calcium↗

PubMed1986

Elemental concentration gradients between subcellular compartments.

To gain information on the mechanisms involved in the establishment and maintenance of subcellular gradients of Na, K, Cl and other elements in the flagellate, Euglena gracilis, we turned to the technique of ultracentrifugal stratification of its intracellular contents, which is achieved without loss of viability or cell rupture. Stratified and non-stratified Euglena were cryofixed for energy-dispersive X-ray microanalysis of Na, K, Cl and other elements in thin freeze-dried cryosections. A number of significant elemental concentration differences (expressed as mmol kg-1 dry weight) were found between chloroplast, nucleus, paramylon granules and open cytoplasm (which contained ribosomes, membranes and macromolecules associated with the cytomatrix) in the non-stratified cells. Stratification caused several ions to be redistributed. For example, we observed a significant increase in K and Cl in the nucleus, which was correlated with the condensation of chromatin. Also Cl, but not Na, decreased significantly in the region of cytoplasm that was cleared of observable ribosomes, membranes and macromolecules associated with the cytomatrix, as well as of observable cytochemical enzyme activity. We conclude from the data that more than half of the Cl in open cytoplasm was adsorbed to or entrapped in material that was removed by ultracentrifugation. Thus, it appears that a close association of at least one ion, Cl, with ultracentrifugable material is involved in maintenance of the measured Cl concentration in the open cytoplasm of the non-stratified cell.

Animals↗

PubMed1986

Disruption of the plasma membrane leads to an influx of Na+ and Cl- but not an efflux of K+ in mouse hepatocytes and erythrocytes.

To determine what mechanisms might be involved in the maintenance of the known extra-/intracellular concentration gradients of Na+, Cl- and K+, small pieces of mouse liver and heparinized blood were appropriately cryofixed. The tissues were cryosectioned and cryosorbed at -100 degrees C or at -40 degrees C. The former temperature prevented diffusion of all ions as measured by electron probe x-ray microanalysis of the thin (0.1 micron) cryosorbed sections of the cells while the latter temperature allowed significant diffusion of Na+ and Cl- into the hepatocytes and erythrocytes but did not allow diffusion of K+ from the hepatocytes or the erythrocytes. These results indicate that the plasma membrane is involved in maintenance of the extra-/intracellular gradients of Na+ and Cl- but that intracellular association of K+ with macromolecules is the main mechanism responsible for maintenance of the extra-/intracellular K+ concentration gradient.

Animals↗

PubMed1985

Subcellular flux of potassium and rubidium in amphibian oocytes.

To determine the net Rb+ influx and K+ efflux at a subcellular level, fully grown and a Ringer's solution where K+ was substituted for by Rb+ on a molar bases. For 40 hrs serial samples of the oocytes were cryofixed and cryosectioned for elemental analysis in mM per kg dry weight using electron probe x-ray microanalysis. Oocyte volume remained constant. Net Rb+ influx showed a slow exponential increase into the nucleus, the yolk-free cytoplasm and the yolk platelets. There was significant K+ efflux from the nucleus but not from the yolk-free cytoplasm or the yolk. The Na+ concentration remained unchanged in all compartments during the course of the experiment. There was however a slow but significant increase in the concentration of Cl- in each of the subcellular compartments but this increase was not sufficient to balance the observed increase in the sum of K+ plus Rb+. Thus Rb+ accumulates selectively in all three subcellular compartments indicating that Rb+ is not a good K+ surrogate in the oocytes. That K+ demonstrates efflux from the nucleus but not from the cytoplasmic compartments is interpreted to suggest that some of the nuclear K+ is lost in exchange for Rb+ but that essentially none of the cytoplasmic K+ is-lost in exchange for Rb+. The findings provide strong evidence for adsorption of Rb+ in the cell.

Animals↗

PubMed1985

Relationships between ice crystal size, water content and proton NMR relaxation times in cells.

Biological specimens were frozen under controlled conditions. We questioned how the size of ice crystals, as measured in cryosectioned and cryoadsorbed sections of these biological specimens, relates to the water content and to the proton NMR relaxation times (T1 and T2) of the unfrozen specimens. The results permit the following conclusions: After rapid freezing in liquid propane cooled in a liquid nitrogen bath, the average size of ice crystals at distances of 150 microns or more from the surface of a particular tissue was always the same. Thus, the average size of the ice crystals was found to be characteristic of the type of biological tissue studied. Linear regression analysis showed average ice crystal size to have a significant correlation coefficient to T1 relaxation time and to water content. Specifically ice crystal size increased with T1 relaxation time and with water content. Multiple regression and path analysis demonstrated a positive correlation between the T1 relaxation time and the ice crystal size variation. Path analysis showed that both water content and T2 relaxation time were less directly correlated with ice crystal size. The findings from the path analysis and other observations show that the average size of ice crystals in subcellular compartments is best predicted by the proton T1 relaxation time. A working model is put forth to explain differences in ice crystal size observed between specimens enriched in globular or in parallel filamentous proteins.

Animals↗