H. J. Schatzmann

The site of action of La3+ in the reaction cycle of the human red cell membrane Ca2+-pump ATPase

Lanthanum (La3+) inhibits the Ca-pump of the red cell by arresting the protein in a phosphorylated form (PI). Similar La3+ concentrations are required to increase the amount of PI and to stop PI-decay. In the presence of La3+ phosphorylation becomes insensitive to Mg2+. PI made in the presence of Mg2+ is not prevented from decaying by subsequent addition of La3+, whereas that made in the absence of Mg2+ is. Taken together, these findings seem to indicate that La3+ blocks the transition between a 1st and a 2nd form of PI.

Die Wirkung von Desoxycorticosteron auf den aktiven Kationenaustausch an Rattenblutzellen

Cold-stored blood cells of rats, which were depleted of potassium and had gained an equivalent amount of sodium instead, were incubated with 500 mg% glucose at 37°C in serum. Under these conditions an extrusion of sodium from and a re-entry of potassium into the cells could be observed. Desoxycorticosterone, when added in a concentration of 1 mg per ml, was able to slow down the rate of this exchange to three fifths of the rate of untreated cells. With blood of adrenalectomised rats, the same effect of DOC was observed, although the rate without DOC was somewhat lower than in the blood of normal animals. There was no statistically significant difference between the DOC-effect in blood of normal and adrenalectomised rats.

Net ATP synthesis by running the red cell calcium pump backwards.

Ca2+ loaded inside-out vesicles from human red blood cells, yielding Ca2+ into a Ca2+ free medium with 4 mM EGTA, 2 mM ADP and 10 mM phosphate, produced an excess of 14.9 pmoles · min−1 · (mg protein)−1 of ATP compared to controls in which the transmembrane Ca2+ gradient was abolished by the ionophore A 23 187.

Intracellular phosphate release by the Na+-K+-activated membrane ATPase

An menschlichen Erythrocyten hemmt Phloretin den passiven Austritt von anorganischem Phosphat. Mit Hilfe dieser Wirkung konnte gezeigt werden, dass die Na+-K+-aktivierte ATPase anorganisches Phosphat nicht direkt nach aussen befördert, sondern im Innern der Zelle freisetzt.

Dependence of the red blood cell calcium pump on the membrane potential

(1) It is shown that the rate of calcium extrusion from intact human red cells is faster at a membrane potential of approximately +50 mV (inside) than at approximately -50 mV. (2) The positive potential applied was the chloride potential of KCl cells in a K-gluconate medium when the Ca2+ sensitive K+ channel was blocked by 0.3mM quinidine. The negative potential resulted from the high K+ permeability in Ca2+ loaded cells (the cells were loaded to a Ca2+ activity in the cell water of about 50 microM). (3) It is further demonstrated that the Ca2+ affinity of the pump ATPase is decreased both at the internal (high affinity) and external (low affinity) site by increasing the proton concentration. Acidification thus inhibits internally and stimulates externally. (4) An indirect effect of the membrane potential on the pump activity via the accompanying pH shifts on either side of the membrane could be ruled out by choosing Ca2+ concentrations which are fully activating at the internal Ca2+ binding site at pH 6.5 and not yet inhibitory at the external Ca2+ binding site at pH 8. (5) The result is compatible with the assumption that the human red cell Ca-pump is exchanging Ca2+ for protons, yet is electrogenic by virtue of a stoichiometry of 1H+:1Ca2+ for this exchange.

A simple fluorometric assay for ampicillin in serum

Behandlung von Ampicillin oder Ampicilloylsäure mit Uranylacetat in der Wärme bei pH 5.2 ergibt ein stabiles fluoreszierendes Produkt. Ausnützung dieser Tatsache und der proteinfällenden Wirkung von Uranylacetat ergibt eine einfache Methode zur Ampicillinbestimmung im Serum mit einer Empfindlichkeit von etwa 0.1 μg/ml. Kombination mit Penicillinasebehandlung erlaubt, Ampicillin in Gegenwart von Ampicilloylsäure zu messen.

Kompetitiver Antagonismus zwischen g-Strophanthin und Corticosteron an isolierten Streifen von Rattenaorten

Corticosterone was shown to have an inhibitory effect on the contraction caused by a cardiac glycoside (g-Strophanthin = Ouabain) in isolated strips of rat aorta. It could be demonstrated that over a tenfold concentration range of Ouabain, the kinetics of this antagonism are in accord with the assumption of a competitive inhibition.

Postnatal decline of (Ca2++Mg2+)-activated membrane ATPase in cattle red cells

Activity of membrane bound (Ca2++Mg2+)-stimulated ATPase, associated with Ca2+ outward transport, in calf red cells is high at birth and declines with a rate constant of 0.041 d−1 after the 3rd week. The decline parallels the disappearance of fetal hemoglobin.

The response to potassium of the Na−K pump ATPase in low-K red blood cells from cattle at birth and in later life

It is shown that in low-K red blood cells of cattle the apparent affinity for K(1/K K app ) at an inhibitory site of the Na−K ATPase increases markedly during the first 3 months of life. This site probably is the Na accepting site at the internal membrane surface and the change in K K app reflects an increase inK Na/K K, the ratio of the true dissociation constants. This effect may explain the concomitant fall in cellular K concentration.

Calcium transport by red blood cell membranes from young and adult cattle

It is shown using inside-out membrane vesicles that cattle red cells extrude calcium by means of a calmodulin sensitive Ca-pump whose activity is high in calves and extremely low in adult cows. The deline is not due to loss of calmodulin susceptibility nor to a drop in Ca-affinity.