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Biomedical subjects

I Szász

Publications and source records attributed to I Szász.

14 recordsLinked to original sources
PubMed1978

Phosphorylation of the Ca2+ pump intermediate in intact red cells, isolated membranes and inside-out vesicles.

Ca2+-entry into intact red cells containing [32P]-ATP increases the phosphorylation of the 150 000 dalton polypeptide of the membrane. This phosphorylation occurs even in Mg2+-depleted red cells. Extracellular lanthanum applied during ATP-depletion further increases the Ca2+-induced phosphorylation. In fragmented membranes or resealed insideout vesicles (IOVs) membrane bound Mg2+ is sufficient to catalyze the phosphorylation of spectrin 2 and Band 3 polypeptides with low concentrations (less than micron of [32P]-ATP. In Ca-EDTA buffers one single polypeptide is phosphorylated which is located in the 150 000 molecular weight region. KmCa for phosphorylation is much lower (0.2 micron) than for active Ca2+ transport (40 micron) in IOVs. Lanthanum induced phosphorylation (up to 250 micron Lafree) is significantly greater than Ca2+-induced phosphorylation. Hg2+ inhibits both Ca2+ and La3+ induced phosphorylation. Ca2+-induced labelling can be rapidly "chased" by unlabelled ATP+Mg2+, but not with EGTA+Mg2+. Dephosphorylation in Ca2+ phosphorylated membranes and IOVs is significantly inhibited by La3+. It can be concluded that the mechanism of La3+ and Hg2+ inhibition of the Ca2+ pump is different in intact cells and isolated membranes or Iovs.

Biological Transport, Active↗
PubMed1978

Effects of lanthanum on calcium-dependent phenomena in human red cells.

Lanthanum (0.25 mM) does not penetrate into fresh or Mg2+-depleted cells, whereas it does into ATP-depleted or ATP + 2,3-diphosphoglycerate-depleted cells, into cells containing more than 3 mM calcium, or cells stored for more than 4 weeks in acid/citrate/dextrose solution. In fresh cells loaded with calcium, extracellular lanthanum blocks the active Ca2+-efflux completely and inhibits (Ca2+ + Mg2+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) activity to about 50%. In Mg2+-depleted cells Ca2+-Ca2+ exchange is inhibited by lanthanum. Ca2+-leak is unaffected by lanthanum up to 0.25 mM concentration; higher lanthanum concentrations reduce leak rate. In NaCl medium Ca2+-leak +/ S.D. amounts to 0.28 +/ 0.08 mumol/1 of cells per min, whereas in KC1 medium to 0.15 +/ 0.04 mumol/1 of cells per min at 2.5 mM [Ca2+]e and 0.25 mM [La3+]e pH 7.1. Lanthanum inhibits Ca2+-dependent rapid K+ transport in ATP-depleted and propranolol-treated red cells, i.e. whenever intracellular calcium is below a critical level. The inhibition of the rapid K+ transport can be attributed to protein-lanthanum interactions on the cell surface, since lanthanum is effectively detached from the membrane lipids by propranolol. Lanthanum at 0.2--0.25 mM concentration has no direct effect on the morphology of red cells. The shape regeneration of Ca2+-loaded cells, however, is blocked by lanthanum owing to Ca2+-pump inhibition. Using lanthanum the transition in cell shape can be quantitatively correlated to intracellular Ca2+ concentrations.

Biological Transport, Active↗
PubMed1977

Transport parameters and stoichiometry of active calcium ion extrusion in intact human red cells.

Ca2+-transport and its energy consumption were studied in intact human red cells loaded with Ca2+ by the aid of the ionophore A23187. After the complete elimination of the ionophore the passive Ca2+-permeability of the membrane returned to its normal low value, except when the intracellular Ca2+-concentration was higher than 3 mM or the ATP level fell below 100 muM. Within these limits the rate of Ca2+-extrusion was independent of the cellular ATP content but was greatly enhanced by increasing [Ca2+]i and reached a plateau at about 1 mM intracellular Ca2+-concentration. The maximum rate of Ca2+-efflux was about 85 mumol/l of cells per min at 37 degrees C, pH 7.4. The activation energy of active Ca2+-extrusion was found to be 15 200 cal/mol, and the optimum pH in the suspension was 7.7. Ca2+-efflux was not connected with the counter-transport of cations. The Ca2+-pump was not affected by ouabain or oligomycin and only partial inhibition could be achieved by the SH-reagents: ethacrynic acid, N-ethylmaleimide and p-chloromercuribenzoate or with propranolol and ruthenium red. An 80 to 95% inhibition of the active Ca2+-extrusion was brought about by 50-250 muM lanthanum, which in the above concentrations caused no aggregation or haemolysis. The inhibition of the Ca2+-pump by lanthanum was found to be reversible, the site of inhibition being at the external surface of the cell membrane. To examine the energy consumption of the Ca2+-extrusion, ATPase activity was assessed by measuring inorganic phosphate liberation in Ca2+-loaded red cells the metabolism of which was inhibited by iodoacetamide + Na+-tetrathionate. Ca2+-activated ATPase activity connected with the Ca2+-pump was distinguished from other Ca2+-ATPases by using the non-penetrating inhibitor, lanthanum. The molar ratio of Ca2+-transported per ATP split was found to be 2 : 1.

Adenine Nucleotides↗
PubMed1977

Haemoglobin and the red cell membrane.

The results presented here indicate that haemoglobin is an integral part of the red cell membrane. The haemoglobin content of the membrane is highly dependent on the Ca++ content of the membrane in health and disease. Changes in the red cell interior alter the whole organization of the membrane and are even reflected in the binding of immunoglobulins to the red cell surface. The preferential binding of Hb-s A2 and S to the membrane has been confirmed. This phenomenon cannot be explained by differences in the charge between these haemoglobins and Hb A.

Binding Sites, Antibody↗
PubMed1976

The use of ionophores of rapid loading of human red cells with radioactive cations for cation-pump studies.

Techniques are described for the rapid loading of intact human red cells with radioactive isotopes of alkali cations or Ca2+ by using ionophorous compounds (nigericin, gramicidin D and A 23187). Loading was rapid and efficient if the membrane potential of the cells was rendered more negative inside. After cation loading the ionophores could be bound to albumin and removed by repeated washings. The ATP and 2,3-DPG contents of the cells were practically unaltered by this treatment. Passive membrane permeability to Na+ and Ca2+ returned to normal. Loaded erythrocytes pumped out Na+ in a ouabain-sensitive and Ca2+ in a lanthanum-sensitive way. Ca2+ -loaded red cells were microspherocytes and exhibited a rapid K+ -efflux. Parallel with the extrusion of Ca2+ cells regained their biconcave shape and normal passive permeability to K+.

Adenosine Triphosphate↗
PubMed1976

Effect of denervation on the longitudinal growth of tubular bones.

The effect of sciatic nerve lesion on the longitudinal growth of tubular bones of the affected extremity has been studied in adolescent rabbits. For the observation of circulation in the bones, intravenously injected Sr85Cl2 solution was used. A retardation of longitudinal growth of the tibia and of the femur on the operated side was noted. Radioactivity in the bones of the operated extremity was always lower than on the control side. For the retarded longitudinal growth, a circulatory disturbance may have been responsible.

Animals↗
PubMed1975

On the mechanism of activation of CaATPase by a single univalent cation.

It has been demonstrated with ox-brain microsome membranes that the mechanism of CaATPase activation by a single univalent cation is different in case of Na+-ont he one hand-and K+ and its congeners-on the other. Whereas Na+ increases the amount of 32-P protein (phosphorylated intermediate), K+ causes only an insignificant increase or decrease compared to the Ca-2+-containing sample. Our findings support the assumption that the altered activity of the Na-K-ATPase (modified by the presence of Ca-2+) is responsible for the univalent cation activation of the CaATPase.

Adenosine Triphosphatases↗