Biomedical subjects
Publications and source records attributed to J Duhm.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
1. Extracellular potassium bicarbonate, ouabain, dipyridamole and the Na+ distribution between red cells and plasma influence Li+ transport across the human red cell membrane. The significance of these parameters for the intraindividual variability of the steady-state ratio of external to internal Li+ was studied in vitro. 2. Elevation of external K+ in the physiological concentration range increases the steady-state distribution ratio Lie+/Lii+ indirectly by increasing the ratio Nae+/Nai+ through activation of the Na+-K+ pump, and directly by inhibiting ouabain-sensitive Li+ uptake. 3. A rise in bicarbonate concentration decreases the Li+ ratio directly by accelerating Li+ uptake through a leak, and indirectly by increasing the Na+ leak, thus reducing the Na+ ratio. 4. Dipyridamole blocks both bicarbonate effects. 5. Ouabain decreases the Na+ ratio and inhibits Li+ uptake by the Na+-K+ pump, thereby exerting two opposite effects on the Li+ distribution ratio. 6. The results confirm the previous observation that the steady-state Li+ distribution depends strongly on the Na+ distribution ratio, i-e., the driving force for Na+-dependent Li+ uphill countertransport. It is concluded that the Na+ distribution between red cells and plasma and the concentrations of K+ and bicarbonate in plasma need to be considered as factors influencing the in vivo Li+ distribution. However, the considerable interindividual differences of Li+ distribution cannot be ascribed to variations in these parameters.
In studies on Li+ net-transport across the human red cell membrane following results were obtained: 1. In K+- and Na+-free choline chloride media, Li+ is transported into the erythrocytes against an electrochemical gradient. This Li+ uphill transport as well as Li+ downhill transport into the cells is inhibited by ouabain, ATP-depletion, and by external K+ and Na+. The effects of K+ and Na+ are relieved at high Li+ concentrations. 2. Ouabain-sensitive Li+ uptake, determined at 10 mM external Na+, does not obey simple Michaelis-Menten kinetics and exhibits a maximum at about pH 7. 3. Ouabain-resistant Li+ downhill transport into erythrocytes increases with rising pH. It is comprised of a saturating component and a component linearly dependent on external Li+. The linear component is partly inhibited by dipyridamole and accelerated by bicarbonate. The bicarbonate effect can be completely blocked by dipyridamole, phlorizin and phenylbutazone. 4. Li+ release is not inhibited by ouabain, ATP-depletion and external K+. It increases with external Na+ concentration, tending to saturate at 150 mM Na+. Na+-independent Li+ release is stimulated by bicarbonate. It is concluded that ouabain-sensitive Li+ uptake is mediated at the K+-site(s) of the Na+-K+ pump. Li+, K+ and Na+ appear to compete for a common site (or sites). The stimulation of Li+ transfer by bicarbonate and the inhibition by dipyridamole suggest a participation of anionic species in ouabain-resistant Li+ transfer. The Na+-dependent Li+ release and the "saturating component" of Li+ uptake are ascribed to the Na+-dependent Li+ countertransport system.
An X-chromosome linked phosphoglycerate kinase deficiency in erythrocytes and leucocytes was discovered in a large German kindred. Seven males of two generations were found to have only 21% of the normal enzyme activity in their erythrocytes, and twelve females of three generations showed various degrees of this defect. The differences in the expression of the deficiency in heterozygote females are explained by the Lyon hypothesis. The deficiency is caused by a variant enzyme, named phosphoglycerate kinase München. Although it differs from the normal enzyme electrophoretically, the two enzymes resemble one another closely in many respects. They have essentially the same Km for the substrates of the backward reaction, identical pH optima and similar rates of thermal inactivation. In contrast to the nine previously described phosphoglycerate kinase deficiencies, all of which are associated with haemolytic anaemia, the carriers of phosphoglycerate kinase München show no overt clinical symptoms. The erythrocyte concentrations of adenine nucleotides and 2,3-diphosphoglycerate are normal.
We have measured the partial pressure of O2 at 50% saturation (P50) and the concentration of various phosphate compounds in the erythrocytes of the bar-headed goose and the guanaco to establish the cause of the high blood O2 affinity in animals who normally reside at high altitude. The same data were obtained in the blood of two goose species, that live at sea level, and in human blood. At standard conditions (pH 7.4, PCO2 40 Torr, 37 degrees C), P50 was 29.7 Torr in the blood of the bar-headed goose and was about 10 Torr higher in the goose species living at sea level. Since the concentration of organic phosphates was not markedly different in the erythrocytes of either goose species we conclude that the hemoglobin of the bar-headed goose reacts more weakly with organic phosphates, which can also be inferred from studies on purified hemoglobin solutions. Likewise, the low P50 of guanaco blood in comparison with human blood can be explained by a reduced interaction of 2,3-bisphosphoglycerate of guanaco hemoglobin compared to the human pigment.
Li+ net-transfer across cell membranes was studied on human erythrocytes and ghosts preloaded with 1-2 mM Li+ and incubated in saline media of varying composition at initial thermodynamic equilibrium for Li+. The following results were obtained: 1. Li+ is extruded from glycolyzing erythrocytes against an electrochemical gradient until a steady-state Li+ distribution is established after 24-28 h. 2. The initial rate of Li+ extrusion is not altered by ouabain or by reduction of ATP levels to less than 25% of the normal value. 3. Replacement of external Na+ by K+ or choline+ abolishes the establishment of an electrochemical Li+ gradient. 4. The Li+ distribution ratio Lie+/Lii+ increases proportional to the ratio Nae+/Nai+ at constant extravellular K+ concentrations. 5. In ghost suspension an uphill Li+ transport is driven by an oppositely directed Na+ gradient. The direction of the Li+ uphill transport can be reversed by reversing the Na+ gradient. From the results it is concluded that the Li+ uphill transport across human red cell membranes is mediated by a Na+-dependent Li+ counter-transport system. This system is not inhibited by ouabain and does not appear to be identical to the Na+-Na+ exchange system described by Garrahan and Glynn.
The influence of the red cell concentration of 2,3-diphosphoglycerate (2,3-DPG, 0.5-26 mumoles/g erythrocytes) on the "CO2-Bohr effect" (pH varied by CO2 at constant base excess) and the "fixed acid-Bohr effect" (pH varied by fixed acid or base at constant PCO2) was studied in human blood at plasma pH values ranging between pH 7.2 and pH 7.6. Elevation of red cell 2,3-DPG concentration leads to a numerical decrease of the "CO2-Bohr coefficient" referring to plasma pH. The "fixed acid-Bohr coefficients" are numerically smaller than the corresponding "CO2-Bohr coefficients" and exhibit a maximum at normal red cell 2,3-DPG concentrations. The Bohr coefficients referring to red cell pH are distinctly higher than those referring to plasma pH, especially at high 2,3-DPG levels. This is due on the one hand to the physico-chemical properties of the intact red cell membrane, and on the other hand to a 2,3-DPG-induced decrease in the ratio deltapHcell/deltapHplasma. From the results it is concluded that 2,3-DPG exerts a dual effect on the Bohr coefficients of whole blood which is mediated 1. by the direct effect of 2,3-DPG on the allosteric properties of hemoglobin (as reflected by changes of the Bohr coefficients referring to red cell pH), and 2. by the effect of 2,3-DPG on deltapHcell/deltapHplasma.
The effect of the concentration of red cell 2,3-diphosphoglycerate (2,3-DPG, 0.5-21 mumoles/g cells) on the buffering properties and on the slope of the relation between the extracellular and intracellular pH (deltapHi/deltapHe) of human blood was studied. The results were evaluated in connection with previous findings concerning the effect of 2,3-DPG on the Donnan ratio rH+ = H+e/H+i. deltapHi/deltapHe decreases with rising red cell 2,3-DPG content as well as with rising extracellular pH. deltapHi/deltapHe and rH+ can be related to each other by the empirical equation deltapHi/deltapHe = 1 + log rH+ = 1 + pHi - pHe. The validity of this equation appears to be restricted to conditions where the Donnan ratio rH+ is altered between 0.3 and 1 either by changes of the red cell concentration of buffering anions such as 2,3-DPG or by changes of the extracellular pH. As determined in suspensions of red cells with intact membranes, the 2,3-DPG-and pH-induced changes of deltapHi/deltapHe lead to proportional changes in the buffering power of the non-bicarbonate buffers of erythrocytes. Due to this effect the buffering power of suspensions of cells containing 5 times the normal concentration of the buffer 2,3-DPG is lower than that of cells with normal 2,3-DPG content (at extracellular pH values above 7). These findings demonstrate that the action of intracellular non-bicarbonate buffers in blood is effectively modulated by the physico-chemical properties of the red cell membrane.
Explore the source record for details and available documents.
In studies on the mechanism of the inhibitory effect of 2, 3-diphosphoglycerate on glycolysis in human erythrocytes, the following results were obtained: 1) Glucose consumption and lactate production are reduced by 70 and 40 per cent relative to normal erythrocytes in red blood cells containing five times the normal amount of 2, 3, -P2-glycerate ("high-diphosphoglycerate" cells) at an extracellular pH of 7.4. The marked dependency of glycolysis on the extracellular pH observed in normal erythrocytes is almost completely lost in the "high-diphosphoglycerate" cells. 2) About 50 per cent of the inhibition of glycolysis in "high-diphosphoglycerate" cells can be accounted for by the 2, 3-P2-glycerate-induced decrease of the red-cell pH. This fall of the red-cell pH which occurs as a conswquence of the Donnan effect of the non-pentrating 2, 3-P2-glycerate anion leads to a reduction of the glycolytic rate due to the properties of the enzyme phosphofructokinase. 3) The remaining part of the inhibitory effect must be attributed to an inhibition by 2, 3-P2-glycerate of glycolytic enzymes. From measurements of glycolytic rates and of the concentrations of glycolytic intermediates in the absence and presence of methylene blue it is concluded that the hexokinase reaction is inhibited by an elevation of 2, 3-P2-glycerate concentration in "high-diphosphoglycerate" cells suggests that also the enzyme pyruvate kinase is inhibited by 2, 3-P2-glycerate. 4) The dependencies of net-change of 2, 3-P2-glycerate concentration on the red-cell pH are identical in normal and "high-diphosphoglycerate" cells indicating that the balance between formation and decomposition of 2, 3-P2-glycerate is the same in erythrocytes with normal and very high compositions of 2, 3-P2-glycerate.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.