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R C Long

Publications and source records attributed to R C Long.

33 records · Page 2Linked to original sources
PubMed1983

NMR analyses of the cold cataract. II. Studies on protein solutions.

Water proton relaxation studies were performed on total soluble protein (TSP) solutions and individual alpha-, beta-, and gamma-crystallin fractions derived from weanling rat lenses, 16 month, and 60- to 70-year-old normal human lenses. The effects of perturbants (temperature and acrylamide) were monitored in order to delineate further the mechanisms involved in the generation of the cold cataract phenomenon (in young lenses) and the role of acrylamide and age in preventing this phenomenon. The data demonstrate a relationship between the relative concentration of the alpha-, beta-, and gamma-crystallin fractions within the lens and the cold cataract phenomenon. It is possible that cross-linking between acrylamide and the gamma-crystallins within the lens alters one or more of the intracytoplasmic protein-water phases. The gamma-crystallin solution showed greater than 35% increase in T2 when 1% acrylamide was added; the young TSP solution T2 increased by approximately 20%. However none of the T2 values for the alpha, beta and old TSP solutions changed significantly when acrylamide was added. The unique response of gamma-crystallin in these experiments suggests a significant role for this protein fraction in the phenomenon associated with cold cataractogenesis. Our data indicate that most of the UVA radiation-induced acrylamide binding occurred with the gamma-crystallins within the lens. We have also noted that only the gamma-crystallin and the young lens TSP solutions become opaque at 4 C while the alpha, beta and "old" TSP solutions remain clear at this temperature. It is suggested that acrylamide exerts its role by cross-linking to one or more of the gamma-crystallins, thereby altering the normal protein water relationship and preventing cold opacification.

Acrylamide↗
PubMed1982

Nuclear magnetic resonance analyses of the cold cataract: whole lens studies.

Pulse nuclear magnetic resonance (NMR) magnetization decay studies were performed on normal and cold cataractous rat lenses. Computer analyses of the decay curves have been interpreted to reflect two types of water within the lens that do not exchange rapidly. Upon lowering the temperature in the presence and absence of 5% acrylamide (a known agent that prevents the cold cataract phenomenon), significant differences in the relaxation rates of one water fraction were noted. 2H (NMR) spectra on young rabbit and human lenses showed temperature-related linewidth changes, which are significantly diminished in lenses incubated in acrylamide. 31P spectra also showed similar inorganic phosphate linewidth changes and also reflected progressive alterations in the metabolic state of these lenses. These studies demonstrate the potential of NMR methods for monitoring physicochemical parameters in the normal and cataractous mammalian lens.

Acrylamide↗
PubMed1979

l-Malate as an Essential Component of the Xylem Fluid of Corn Seedling Roots.

Corn seedling xylem exudate has a pH of 5.30 +/- 0.05 due to the presence of 10 millimolar malate which has a pK(a) of 5.13. This concentration of malate tends to buffer the xylem fluid at this pH. Exogenous treatment of corn seedling roots with CaCl(2) caused a concentration-dependent decrease in the pH of the xylem fluid as well as a decrease in the volume of fluid secreted into the xylem. Exogenous 50 millimolar CaCl(2) decreased exudate volume to 8% of control within 0.5 hour. Nitrate and malate deposition into the xylem was prevented by pretreatment in 5 millimolar CaCl(2); nitrate deposition was resumed shortly after resumption of malate deposition. Fifty millimolar l-tartrate, an inhibitor of the Cl(-), malate-activated ATPase (in vitro) of the tonoplast, also decreased exudate volume as well as slightly lowering exudate pH. The osmolality of the exudate was found to be constant at 70 +/- 11 milliosmomoles per kilogram in all treatments. Dixon plots (log of exudation rate versus pH of exudate) indicated a pK(a) of 5.11 for the exudation process which is very close to the pK(a) of l-malate (5.13). In addition, a Dixon plot of the l-glutamine deposition (l-glutamine being the major form of reduced nitrogen in the exudate) versus pH also indicated a pK(a) near 5.15.The pH optimum for glutamine transport into the xylem was 5.5. Deposition of glutamine into the xylem may be regulated by the xylem pH (5.30 +/- 0.05) which in turn may be regulated by the presence of 10 millimolar malate. It is proposed that the transport of glutamine into the xylem may provide the driving force for the exudation process.

Journal Article↗
PubMedDate not supplied

Noninvasive measurement of viable cell number in tissue-engineered constructs in vitro, using 1H nuclear magnetic resonance spectroscopy.

Noninvasive monitoring of tissue-engineered constructs is of critical importance for accurate characterization of constructs and their remodeling in vitro and in vivo. This study investigated the utility of (1)H NMR spectroscopy to noninvasively quantify viable cell number in tissue-engineered substitutes in vitro. Agarose disk-shaped constructs containing betaTC3 cells were employed as the model tissue-engineered system. Two construct prototypes containing different initial cell numbers were monitored by localized, water-suppressed 1H NMR spectroscopy over the course of 13 days. (1)H NMR measurements of the total choline resonance at 3.2 ppm were compared with results from the traditional cell viability assay MTT and with insulin secretion rates. Results show a strong linear correlation between total choline and MTT (R (2) = 0.86), and between total choline and insulin secretion rate (R (2) = 0.90). Overall, this study found noninvasive measurement of total choline to be an accurate and nondestructive assay for monitoring viable betaTC3 cell numbers in tissue-engineered constructs. The applicability of this method to in vivo monitoring is also discussed.

Algorithms↗
PubMedDate not supplied

Effects of short-term hypoxia on a transformed cell-based bioartificial pancreatic construct.

Hypoxia is an adverse condition that can jeopardize the function of a bioartificial pancreatic construct. In this study we have investigated the effects of short-term hypoxic exposure (up to 24 h) on the bioenergetic status, metabolism, and insulin secretion of perfused pancreatic constructs composed of alginate/poly-L-lysine/alginate (APA) encapsulated mouse insulinoma betaTC3 cells. The bioenergetic status of the encapsulated cells was monitored noninvasively with the aid of 31P NMR spectroscopy, while glucose, lactate, and insulin concentrations were measured with off-line assays from media samples removed from the perfusion loop. Our results demonstrate that in freshly prepared constructs insulin secretion was not affected by the hypoxic conditions, although intracellular ATP concentration decreased and glucose consumption increased. Alternatively, in constructs that were maintained in our perfusion system for at least 10 days, identical hypoxic conditions resulted in a decreased insulin secretion concomitant to a decreased intracellular ATP concentration and increased glucose consumption. These results suggest that the effects of hypoxia on a transformed cell-based pancreatic construct are not constant throughout the duration of an in vitro culture. The observed differences are attributed to the significant cell growth and rearrangement that occurs with time during an in vitro culture of the constructs.

Adenosine Triphosphate↗