Bicarbonate and chloride transport across rat ileal basolateral membrane

The mechanisms of HCO ₃ ^– and Cl^– transport across basolateral membranes from rat ileum were investigated in isolated vesicles by means of uptake experiments. Neither Cl^–/HCO ₃ ^– exchanger nor Na⁺–(HCO ₃ ^– )_n cotransport seem to be present in ileal basolateral membranes. Moreover Cl^– uptake is unaffected bycis Na⁺ and/or K⁺ gradients, indicating the absence of Na⁺–Cl^–, K⁺–Cl^– and Na⁺–K⁺–2Cl^– symport activity. An electrically conductive pathway seems to be responsible for both HCO ₃ ^– and Cl^– fluxes. Evidence is also given for the presence of a Na⁺/H⁺ exchanger at the basolateral pole of ileal enterocytes.     

Effects of corpora cardiaca extract,furosemide and ion substitution on sodium and chloride flux in perfused Malpighian tubules ofLocusta

Treatment with the co-transport inhibitor, furosemide decreased³⁶Cl^– flux across perfused Malpighian tubules ofLocusta. However, exclusion of³⁶Cl^– from the bathing medium had not effect on²²Na⁺ flux whereas substitution of bathing medium Na⁺ by K⁺ increased³⁶Cl^– flux. Diuretic extract of corpora cardiaca increased²²Na⁺ (by 106%) and³⁶Cl^– (by 335%) fluxes differentially.     

Concerning the ionic basis of presynaptic inhibition.

The superfused rat cuneate nucleus has been used to investigate the sensitivity of primary afferent terminals and of evoked primary afferent depolarization (PAD) to alterations in extracellular K+ and Cl- ions levels. Results indicate that PAD is caused by an efflux of Cl- from primary afferent terminals rather than by an increase in extracellular K+.     

Effects of high hydrostatic pressures on the movements of Na+, K+ and Cl− in isolated eel gills

Summary Hydrostatic pressure applied to isolated eel gills induces changes in the tissue, Na⁺, K⁺ and Cl^– contents. It also inhibits the activity of the (Na⁺+K⁺) ATPase. Results are discussed in terms of an effect of pressure on the Na⁺ and Cl^– pumps and on the passive permeability processes.A. P., Chargé de Recherches du F. N. R. S.; R. G., Chercheur qualifié du F. N. R. S., We are grateful to Prof. A. Distèche and E. Schoffeniels for their advice throughout this work. We also want to thank Mr J. M. Theate and Mrs C. Marchand-Coquay for their valuable technical assistance.     

Monovalent cation conductance in liposomes induced by ionophore A23187

Summary In the absence of divalent cations, ionophore A23187 supports low rates of monovalent cations loss (Na⁺>K⁺) from unilamellar liposomes containing the sulfate salts. Monovalent cation efflux is optimal when a pH gradient (interior alkaline) is applied. The maximum observed rate of 0.56 ngion K⁺·min^–1·nmole^–1 A23187 is insufficient to account for the rates of K⁺ efflux induced by the ionophore in mitochondria (150 ngion K⁺·min^–1·nmole^–1 A23187). These studies therefore support the concept that A23187 induces loss of K⁺ from mitochondria by removal of regulating divalent cations from an endogenous K⁺/H⁺ exchanger.These studies were supported in part by United States Public Health Services Grant HL09364.     

A histochemical demonstration of the Na++K+-ATPase activity in the thyroid and the effect of cyclic adenosine monophosphate (c-AMP)

Summary With a suitable modification of the Farquhar and Palade technique the Na⁺+K⁺-ATPase activity in guineapig thyroid is demonstrated. The addition of c-AMP (5×10^–6 M or 1.5×10^–5 M) to the incubation media produced an apparent intensification of the Na⁺+K⁺-ATPase activity in the thyroid.This work was supported by a grant from ZMNU of Serbia.     

Vanadate: Non-selective inhibition of transepithelial transport of Na+, H+ and water

Summary In the isolated urinary bladder of the toad, 10^–5–10^–4M orthovanadate produces inhibition of the active transport of Na⁺ and H⁺ ions as well as of antidiuretic hormone-mediated osmotic flow of water. Since transport of H⁺ ions and osmotic water flow are not inhibited when (Na⁺+K⁺)-ATPase is inhibited by ouabain, biological actions of vanadate are not necessarily related to inhibition of (Na⁺+K⁺)-ATPase.This research was supported by grant AM-14915 from the National Institutes of Helath.     

Die Abhängigkeit der Ca++-Aufnahme isolierter Mitochondrien des Herzmuskels von der Na+-und K+-Konzentration als mögliche Ursache der inotropen Digitaliswirkung

Summary In isolated mitochondria of heart muscle from rabbits and oxen there is, under suitable conditions, an accumulation of Ca⁺⁺, which is significantly enhanced by elevating the K⁺/Na⁺ quotient of the incubation medium. K-strophanthine (10^–5–10^–7) does not influence the accumulation of Ca⁺⁺ by the mitochondria of heart muscle. Therefore the intracellular increase in exchangeable Ca⁺⁺ observed after digitalis-glycosides could be explained by a decrease of the intracellular K⁺/Na⁺ quotient, which is caused by inhibition of the membrane ATPase and diminishes the capacity for Ca⁺⁺ accumulation in mitochondria.     

Insulin effect in vitro on human erythrocyte plasma membrane

Summary The effect of porcine insulin has been tested in vitro on human erythrocyte plasma membrane (Na⁺–K⁺) and Mg²⁺-ATPase activities as well as on membrane fluidity. The results indicate that the hormonal treatment significantly inhibits (Na⁺–K⁺)-ATPase activity, and at the same time decreases membrane fluidity.This investigation has been supported by Consiglio Nazionale delle Richerche, Rome, Italy.     

Cytochemical localization of the K+ regulation interface between blood and brain

Summary Phosphatase activity identified with Na⁺–K⁺-ATPase was localized at the basal surface of cerebral cortical capillary endothelium by perfusion with a p-nitrophenyl phosphate-strontium medium. The relationship of this to the blood-brain barrier to K⁺ is discussed.     

The activation of membrane ATPase by ouabain in several tissues of the golden hamster (Mesocricetus auratus) in the absence of potassium

Summary The activity of the membrane ATPase of 5 organs of the golden hamster was increased by 10^–7–10^–3 moles/l ouabain in K⁺-free medium. In similar experiments on rats no increase was observed.     

The effect of temperature on the ouabain-sensitivity of Na+−K+-activated ATPase and fluid secretion by the Malpighian tubules ofLocusta

Summary Temperature markedly affected the ouabain-sensitivity of both the Na⁺–K⁺-activated ATPase activity and the secretion of fluid by the Malpighian tubules ofLocusta. Varying the K⁺ concentration in the bathing medium did not affect the ouabain-sensitivity of the fluid secretory process.     

Studies on hydrogen,halides and thiocyanate ions in dioxane-water mixtures at various temperatures

Summary The free enrgies of transfer (G _t ⁰ ) of H⁺, Cl^–, Br^–, I^– and SCN^– ions from water to 10, 20, 30 and 40% dioxanewater mixtures have been studied from potentiometric measurements. For anions the G _t ⁰ values are in the order Cl^–>Br^–>SCN^–>I^–.     

The action of ouabain in promoting the release of catecholamines

Summary It is suggested that ouabain promotes catecholamine release by causing a rise in intracellular Na⁺ which, in turn, causes an elevated steady-state level of intracellular Ca²⁺. It is suggested that the Na⁺–K⁺-ATPase is not directly involved in exocytosis at either adrenergic or cholinergic synapses.     

Toxicity of ouabain on Drosophila melanogaster

Summary Ouabain, also called g-strophantin, is an inhibitor of the Na⁺/K⁺-activated plasma membrane ATPase. Treatment of Drosophila melanogaster with 3–6 mM of this substance leads to a markedly reduced survival of the flies.     

Oscillatory after-potentials and triggered-automaticity in mammalian ventricular muscle fibres at high resting potentials

Summary Oscillatory after-potentials and triggered-automaticity were observed in dog ventricular muscle fibres when the fibres were exposed to K⁺-free, high-Ca⁺⁺-solutions after K⁺-free, Ca⁺⁺-free perfusion. They appeared at membrane potentials more negative than –60 mV.     

Age dependent changes in Na+−K+, activated ATPase activity of locust rectum

Summary Na⁺–K⁺, activated ATPase showed an increase in activity at the beginning of the 5th instar and adult life. This was followed by a relatively constant level of activity which, in larval preparations only, was not maintained but decreased with the onset of metamorphosis.     

Effect of potassium and norepinephrine on the tone of the isolated artery: Changes by ouabain pretreatment

Zusammenfassung Vorbehandlung von Arterienstreifen mit g-Strophantin (>10^–8 g/ml) kehrt die mechanische Reaktion auf K⁺-Änderungen im Bereich von 1 bis 10 mM KCl, nicht aber die K⁺-Wirkung auf die Kontraktion durch Noradrenalin oder Barium um. Danach könnte die K⁺-Dilatation der Arterien auf der Aktivierung einer elektrogenen Na⁺-Pumpe beruhen.

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The authors gratefully acknowledge the technical assistance by Mrs.B. Heinemann.     

Cl−/HCO 3 − exchanger is operative in isolated enterocytes from rat jejunum

Enterocytes isolated from rat jejunum were tested for the existence of a Cl^–/HCO ₃ ^– exchange, previously evidenced in basolateral membrane vesicles but not in brush border. Cells were found to retain functional integrity and transport capabilities long enough to allow Cl^– fluxes to be measured. Both efflux and uptake experiments indicate that a Cl^–/HCO ₃ ^– antiport, inhibited by 4,4-diisothiocyanostilbene-2-2-disulfonic acid (DIDS), is functional under resting conditions.     

Inhibition of glucose transport in human erythrocytes by 2,3-dioxoindole (Isatin)

10 mM isatin (2,3-dioxoindole) inhibited glucose influx into human erythrocytes by over 30%. The inhibition is of the competitive type, where the affinity constant (K_t) was increased from 5.71 (control) to 11.11 mM in the presence of isatin with no change in V_max (130 nmol/min/ml packed cells). The observed inhibition of sugar transport by isatin was not mediated through membrane–SH groups accessible to iodoacetate, iodoacetamide, DTNB, DNP or sodium arsenite. Isatin inhibited sugar transport in the presence of 2 mM harmaline, an alkaloid inhibitor of Na⁺, K⁺–ATP_ase activity. The inhibition was non additive which suggests that these two compounds interact with the same or a similar site on the erythrocyte membrane.