Potassium Ions and the Binding of Cardiac Glycosides to Mammalian Cells

Baker, P. F.; Willis, John S.

doi:10.1038/226521a0

Cited by 140 publications

(64 citation statements)

References 13 publications

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“…A direct comparison between the acute and chronic effects of ouabain can be made as follows (data taken from the experiment shown in Figure 3); HeLa cells treated chronically for 24 h with 10-8M ouabain in normal Krebs solution have the same number of free sites (0.27x 106 sites/cell; s.e.+0.02; n=3) as those treated acutely for 10 min with 5 x 10-8M ouabain in K-free Krebs (0.26x 106 sites/cell; s.e.±0.01; n=4). The increase in efficacy is equal to the concentration difference (times 5) times the inhibitory effects of potassium on the ouabain binding (times 10; Baker & Willis, 1970;. At a first approximation, therefore, chronic exposure to low concentrations of ouabain leads to a 50 fold increase in drug efficacy.…”

Section: Discussionmentioning

confidence: 99%

DOWN‐REGULATION OF THE SODIUM PUMP FOLLOWING CHRONIC EXPOSURE OF HeLa CELLS AND CHICK EMBRYO HEART CELLS TO OUABAIN

Aiton

Lamb

Ogden

1981

British J Pharmacology

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HeLa cells and primary cultures of embryonic chick heart cells were grown in medium containing low concentrations of ouabain for 24 h. Compared with normal cells, cells grown in ouabain have fewer free sodium pump sites, an increased intracellular sodium concentration and a decreased intracellular potassium concentration. The cells are able to maintain their intracellular ion contents because the remaining pump sites have an increased turnover rate. When cells that have been chronically exposed to ouabain are returned to normal growth medium, the sodium pump site numbers increase; the recovery process begins within 6 to 8 h and is complete within 24 h. Recovery of pump site numbers is primarily dependent upon de novo protein synthesis since the protein synthesis inhibitor, cycloheximide, prevents recovery.

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Section: Discussionmentioning

confidence: 99%

DOWN‐REGULATION OF THE SODIUM PUMP FOLLOWING CHRONIC EXPOSURE OF HeLa CELLS AND CHICK EMBRYO HEART CELLS TO OUABAIN

Aiton

Lamb

Ogden

1981

British J Pharmacology

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“…However, in a study with cultured HeLa cells, Kf slowed the rate of glycoside binding but not that of glycoside release [24]. It is not known, however, to what extent glycoside binding and release in whole cells may be related to membrane turnover or other metabolic events.…”

Section: Potassium Effectsmentioning

confidence: 97%

Ouabain Reaction with Microsomal (Sodium‐plus‐Potassium)‐Activated Adenosinetriphosphatase

Siegel

Josephson

1972

European Journal of Biochemistry

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Microsomal (Na+ + K+)-activated adenosinetriphosphatase from eel electroplax binds ouabain in a slow reaction. The rate of binding is modified by enzyme ligands, including nucleotides, orthosphosphate, p-nitrophenylphosphate, carbamylphosphate, Mg2+, Na+, and K+. The actions of these ligands on the enzyme were studied by measuring their effects on the initial rate of ouabain binding.The stimulatory actions ATP, ADP, and Pi depend on the formation of enzyme -Mg -phospholigand complexes. Free nucleotides and Pi are inhibitory. Two alternative pathways for ouabain binding are confirmed : (a) Na+-stimulated, ATP-dependent, and (b) Na+-inhibited, Pi-dependent. I n addition, it is shown that the Na+-stimulated path may depend on any of the organic phosphate ligands, including p-nitrophenylphosphate, carbamylphosphate and ADP. I n contrast, the Na+-inhibited path is supported only by MgHPO, or free Mg2+. There is evidence for non-identical Na+-binding sites : the "a],., value for sttimulation is 20 mM while that for inhibition is 4 mM. I n the presence of both ATP and Pi, the Na+-potentiated-ATP path is favored. K+ inhibits both pathways reversibly and exhibits competition with Na+ and with MgHPO,.ATP decreases the enzyme affinity for K+ while Na+ plus ATP increase the affinity for K+. Since the Pi enzyme complex is observed only in the absence of both Na+ and K+, it is considered a side path not related to the catalytic cycle.The influences of the ligands on ouabain binding may be related to their effects on the enzyme catalytic cycle. There are two general hypotheses for the ligand effects on ouabain reactivity of (Na+ + K+)-ATPase. One, proposed by Sen et al. in 1969, is based on the formation of phosphorylenzyme. The observations are also consistent with an alternative hypothesis which is proposed as follows: (a) the enzyme reactivity with ouabain is increased by the formation of an enzyme -Mg -phospholigand complex regardless of whether the enzyme is also phosphorylated, (b) Na+-activated enzyme has increased affinity for the organic phosphates, which may be considered as substrates, and decreased affinity for Pi and free Mg2+, and (c) K+-activated enzyme has decreased affinity for all the ligands.

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“…K + ions and ouabain compete for the same binding sites (Baker and Willis, 1970); therefore, a high bath [K + ] would decrease the effect of ouabain. Because, as previously shown, a low [K + ] (5 mmol l -1 ) irreversibly inhibits fluid secretion rates, the secretion assay was carried out in control Ringer (50 mmol l -1 K + ).…”

Section: The Effect Of Rubidium On the Basolateral Membrane Potentialmentioning

confidence: 99%

K+ transport in Malpighian tubules ofTenebrio molitorL.: a study of electrochemical gradients and basal K+uptake mechanisms

Wiehart

Nicolson

Kerkhove

2003

Journal of Experimental Biology

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SUMMARYMalpighian tubules of the mealworm Tenebrio molitor were isolated for intracellular measurement of basolateral (Vbl) and,indirectly, apical (Vap) membrane potentials. In control Ringer (50 mmol l-1 K+, 140 mmol l-1Na+), Vbl was 24mV, cell negative, and Vap was 48 mV, cell negative with reference to the lumen. Ion substitution experiments involving K+ and Na+indicated that both Vbl and Vap were sensitive to the bathing K+ concentration, with the change in Vap being 60-77% that of Vbl. A 10-fold drop in bath [K+] irreversibly decreased fluid secretion rates from 6.38±0.95 nl min-1 (mean ± S.E.M.) to 1.48±0.52 nl min-1 (N=8). In the presence of 6 mmol l-1 Ba2+, a blocker of basal K+ channels,fluid secretion rates reversibly decreased and the hyperpolarization of both Vbl and Vap seen in 50 mmol l-1 and 140 mmol l-1 K+ indicated a favourable electrochemical gradient for basal K+ entry. In 5 mmol l-1 K+, Ba2+ induced two different responses: Vbl either hyperpolarized by approximately 10 mV or depolarised by approximately 14mV, according to the electrochemical gradient for K+, which was either inward or outward in low bath[K+]. Rubidium, a `permeant' potassium substitute, caused a hyperpolarization of Vbl, indicating the specificity of K+ channels found in Tenebrio tubule cells. Other possible K+ uptake mechanisms located in the basolateral membrane were investigated. Blocking of the putative electroneutral Na+/K+/2Cl- cotransporter by 10 μmol l-1 bumetanide reversibly decreased fluid secretion rates, with no detectable change in membrane potentials. Ouabain (1 mmol l-1), an Na+/K+-ATPase inhibitor, irreversibly decreased fluid secretion rates but had no effect on electrical potential differences either in the absence or presence of Ba2+. The results implicate K+ channels, the Na+/K+/2Cl-contransporter and the Na+/K+-ATPase in basal K+ and fluid transport of Tenebrio tubule cells.

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Potassium Ions and the Binding of Cardiac Glycosides to Mammalian Cells

Cited by 140 publications

References 13 publications

DOWN‐REGULATION OF THE SODIUM PUMP FOLLOWING CHRONIC EXPOSURE OF HeLa CELLS AND CHICK EMBRYO HEART CELLS TO OUABAIN

DOWN‐REGULATION OF THE SODIUM PUMP FOLLOWING CHRONIC EXPOSURE OF HeLa CELLS AND CHICK EMBRYO HEART CELLS TO OUABAIN

Ouabain Reaction with Microsomal (Sodium‐plus‐Potassium)‐Activated Adenosinetriphosphatase

K+ transport in Malpighian tubules ofTenebrio molitorL.: a study of electrochemical gradients and basal K+uptake mechanisms

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