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R A Kleps

Publications and source records attributed to R A Kleps.

10 recordsLinked to original sources
PubMed1994

Inhibition of the calcium paradox in isolated rat hearts by high perfusate sucrose concentrations.

If a colloid osmotic (oncotic) pressure gradient develops across the myocyte membrane during the calcium paradox, adding an oncotic agent to the perfusate should be inhibitory. After 10-min perfusion with Ca(2+)-free Krebs-Henseleit (KH) buffer under constant flow at 34 degrees C, myoglobin release was measured from Langendorff hearts reperfused with Ca(2+)-containing KH buffer. When the Ca(2+)-free medium contained 200 mM sucrose, myoglobin release was reduced to 5% of that observed in the absence of sucrose, a change that was not seen when 200 mosM NaCl, choline chloride, LiCl, or glycerol was added. Replacement of 75 mM NaCl in the perfusate with 150 mM sucrose resulted in myoglobin release values that were 4% of the control. Plots of myoglobin release against sucrose concentration under these hypertonic and isotonic conditions yielded similar though separate curves. Sucrose also inhibited increases in wet weight-to-dry weight ratio and decreases in ATP and phosphocreatine contents. These results support the hypothesis that an oncotic pressure gradient arises during the calcium paradox at the moment of increased membrane permeability and plays a major role in its development.

Animals↗
PubMed1990

Inhibition of chloride binding to the anion transport site by diethylpyrocarbonate modification of Band 3.

The line widths of 35Cl- nuclear magnetic resonances were used to measure chloride binding by Band 3. Since this procedure relates directly to binding, the data obtained may be interpreted more unequivocally than affinities derived from kinetic data which could be related to either translocation or binding. Chloride binding to the active sites in Band 3 was assessed from that portion of the total line width which was sensitive to 4,4'-dinitrostilbene-2,2'-disulfonic acid. These sites appeared to be completely inhibited by treatment of erythrocyte membranes with diethylpyrocarbonate. This result is consistent with our previous observation that this reagent inhibits anion transport in resealed erythrocyte ghosts (Izuhara, Okubo & Hamasaki, 1989, Biochemistry 28:4725-4728). Hydroxylamine could not reverse the diethylpyrocarbonate inhibition of chloride binding to Band 3. The pH-dependence of diethylpyrocarbonate reactivity suggests that the modified residues may be those of histidine.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1990

Gluconeogenesis in the liver of tumor rats.

Altered gluconeogenesis is frequently observed in cancerous hosts. To define its derangements in the liver, we studied glucose and glycogen production in the perfused livers of tumor-bearing rats using 13C NMR spectroscopy. Nine Fischer 344 rats were inoculated with mammary adenocarcinoma. After 5 weeks, the livers were removed and perfused with Krebs buffer containing 8 mM L-[3-13C]alanine, and 13C NMR spectroscopy was performed. Nine pair-fed rats were studied as controls. The peak heights of glucose and glycogen in the 13C NMR spectra of the perfused livers and final perfusates of the two groups of rats were compared. We found comparable amounts of C1-labeled glucose and glycogen in the two groups, but C2- to C5-labeled and C6-labeled glucose and glycogen, as well as total 13C-labeled glucose and glycogen, appeared in smaller quantities in the tumor rats than in the pair-fed rats. These findings suggest that appreciable amounts of unlabeled glycerol were utilized by both groups, but less so by the tumor rats than the pair-fed rats. In addition, there was decreased production of oxaloacetate through pyruvate dehydrogenase and the Krebs cycle in the livers of the tumor rats, where the overall metabolism of alanine into glucose and glycogen was also reduced.

Adenocarcinoma↗
PubMed1987

Surface coil holder for Signa.

A surface coil holder is described for the General Electric Signa spectrometer. This allows for accurate positioning of the 31P coil relative to that of the 1H coil used for tissue slice localization.

Arterial Occlusive Diseases↗
PubMed1984

Intracellular pH of the urinary bladder and red blood cells of the fresh water turtle.

Intracellular pH is thought to play an important role in several aspects of cell function including urinary acidification. The turtle urinary bladder is capable of urinary acidification in vitro and it is considered an analogue of the mammalian distal nephron. In the present study we measured intracellular pH in the epithelial layer of the turtle urinary bladder utilizing phosphorus nuclear magnetic resonance. In 14 experiments, the intracellular pH of the stripped turtle bladder epithelium bubbled with compressed air was 6.91 +/- 0.02; in turtle red blood cells the mean intracellular pH was 6.97 +/- 0.05 (n = 20), a value not significantly different from the pH value obtained in the turtle bladder. Gassing the turtle bladder with 95% air and 5% CO2 while maintaining the extracellular pH constant resulted in a rapid decrease in intracellular pH. Lowering of extracellular pH with HCl also resulted in a decrease in intracellular pH. The results demonstrate that phosphorus nuclear magnetic resonance allows rapid, noninvasive measurement and frequent monitoring of intracellular pH in the turtle bladder.

Animals↗
PubMed1983

A phosphate-analogue probe of red cell pH using phosphorus-31 nuclear magnetic resonance.

In order to find a suitable marker of intraerythrocytic pH in a phosphorus-31 nuclear magnetic resonance (31P NMR) system, analogues of inorganic phosphate were studied. Fluorophosphate (pKa = 4.7) and phosphite (pKa = 6.4) chemical shifts and coupling constants were found to be pH sensitive but at pH ranges too low to be useful for the study of fresh red cells. Methylphosphonate (pKa = 7.6) showed ideal characteristics for a pH probe: its chemical shift was far downfield for red cell phosphates and showed a large pH dependence near its pKa (delta pH/delta delta = 0.46 pH/ppm). Methylphosphonate readily entered red cells [influx 7.8 microM (mL of RBC)-1 h-1] and did not appear to alter glucose consumption or hemoglobin-oxygen affinity in intact cells. NMR spectra were obtained on eight samples of fresh red cells incubated for 30-60 min with methylphosphonate. Chemical shift differences between the extracellular and intracellular methylphosphonate signals were found to be predictive of the transmembrane pH gradient. The extracellular pH was 7.336 +/- 0.031 (range 7.31-7.41), while the intracellular pH was 7.202 +/- 0.034 (range 7.14-7.23), and the transmembrane pH gradient measured 0.129 +/- 0.008 (range 0.11-0.14). Methylphosphonate is a useful probe of pH in the 31P NMR spectroscopic study of red cells.

2,3-Diphosphoglycerate↗
PubMed1976

Cyclization of the phosphorus chain of the methylene-bridged analogs of adenosine triphosphate.

The phosphorus-containing side chains of two methylene-bridged analogs of adenosine triphosphate have been cyclized to produce the corresponding analogs of monoadenosine-5'-trimetaphosphate. (The structures are given in the journal.) The molecules, which were generated in anhydrous media through a carbodimide-mediated condensation, were characterized by 31P nuclear-magnetic resonance, and the white-noise 1H decoupled spectra were simulated. These molecules are quite reactive and readily converted to their corresponding linear forms upon hydrolysis. The second structure contains an asymmetric phosphorus atom, and both of the possible cyclic molecules have been observed and the diasteroisomeric mixture has been isolated.

Adenosine Triphosphate↗
PubMed1976

Carbodiimide-intermediated esterification of the inorganic phosphates and the effect of tertiary amine base.

Detailed analysis of appropriate 31P nuclear-magnetic-resonance spectra shows that under the usual laboratory conditions, carbodiimide-induced condensation of orthophosphoric acid in a number of solvents leads to condensation only slightly beyond the metaphosphate composition in the presence of strong tertiary amines; whereas in the absence of amine, the condensation proceeds into the ultraphosphate region about halfway between the metaphosphate and phosphoric anhydride compositions. With amine, the principal product consists of the cyclic trimetaphosphate anion, with one of the nonbridging oxygen atoms substituted by the urea resulting from hydration of the carboiimide, i.e., (O2-) P-O-P(O2-) -O-P(O) [N[CH(CH3)2] see article [C(O)NHCH(CH3)2]] for the condensation with diisopropylcarbodiimide. Without amine, the major product is the 1,5-mu-oxotetrametaphosphate anion see article. The well-known carbodiimide-mediated phosphorylation of alcohols with orthophosphoric acid is shown to be directly attributable to the high reactivity of the phosphate branch groups of the carbodiimide-generated ultraphosphates.

Amines↗
PubMed1974

Cyclization of the phosphate side chain of adenosine triphosphate: formation of monoadenosine 5'-trimetaphosphate.

Monoadenosine 5'-trimetaphosphate has been prepared from adeno-sine 5'-triphosphate by a carbodiimide-mediated condensation. The molecule was characterized by (3l)P nuclear magnetic resonance, and its (31)P spectrum was simulated through the assumption of a three-phosphorus spin system. The molecule is highly reactive and is rapidly converted to adenosine triphosphate upon contact with water.

Adenosine Triphosphate↗