Amiloride: a potent inhibitor of sodium transport across the toad bladder

Bentley, P. J.

doi:10.1113/jphysiol.1968.sp008460

Cited by 387 publications

(160 citation statements)

References 18 publications

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“…This increased current was stable for at least 5 min. The diuretic drug, amiloride, which blocks passive sodium fluxes in amphibian epithelia (19), had no effect on the current at a concentration of 1 mM. It was concluded, then, that Na+ was not the current-carrying ion, but that Na+ did indirectly affect the current.…”

Section: Resultsmentioning

confidence: 95%

Electrical currents through full-grown and maturing Xenopus oocytes.

Robinson¹

1979

Proc. Natl. Acad. Sci. U.S.A.

108

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An extracellular vibrating electrode was used to map the current pattern around Xenopus laevis oocytes. Current was found to enter the animal hemisphere and leave the vegetal hemisphere; in fully grown oocytes from which the follicle cells had been removed, the maximal current density was about 1 uA/cm2. This current decreased to nearly zero in response to progesterone and several other maturation-producing agents. In the case of progesterone, the decline began within a few minutes of the addition of the hormone and proceeded with a half-time of about 20 min.An analysis of the effects on the current of the removal or addition of various ions and drugs led to the inference that the major current-carrying ion was chloride and that the chloride permeability was controlled by calcium. An ubiquitous feature of nonmammalian animal eggs is the presence of an animal-vegetal axis. The nucleus of the egg is generally displaced toward the animal pole and this pole is the site of polar body formation. In many amphibian eggs, the axis is readily distinguished by the pigment accumulation at the animal pole and the yolk mass at the vegetal pole. Superimposed on this visible polarity is a developmental polarity: the animal pole gives rise to the ectodermal parts of the embryo and the vegetal pole, to the endodermal. (For a recent review, see refs. 1 and 2.) When the full-grown anuran oocyte is exposed to progesterone, a sequence of events is triggered, leading to the reinitiation of meiosis and formation of a fertilizable egg. This process is also a polar one. The basal portion of the germinal vesicle is the first to break down as the entire germinal vesicle moves toward the animal pole (3).Our knowledge of the physical forces that might produce such asymmetries and direct polar movements remains limited. The oocytes are randomly oriented in the ovary; thus gravity is not the causal agent. Strong evidence has now accumulated in the case of fucoid algae eggs that electrical currents and ion gradients are involved in transducing environmental asymmetries into cellular polarity (4-6). Electrical currents associated with growth and localization processes have also been shown to exist in insect oocytes (7), pollen tubes (8), and regenerating Acetabularia (9). There are also a few older surface potential measurements from which the existence of polar currents in animal eggs can be inferred (10). It is against this background that this investigation of animal-vegetal currents in Xenopus oocytes and eggs was begun.METHODS AND MATERIALS Sexually mature Xenopus laevls females were obtained from the South African Snake Farm, Fish Hoek, South Africa. To obtain oocytes, females were anesthetized by chilling in an ice bath, portions of their ovaries were removed, and the oocytes were then manually dissected from their follicles. In some cases, the remaining follicle cells were removed by a 5-min treatment with Pronase (50 ;tg per ml in Steinberg's solution).A vibrating platinum electrode was used to measure extracellular currents. T...

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Section: Resultsmentioning

confidence: 95%

Electrical currents through full-grown and maturing Xenopus oocytes.

Robinson¹

1979

Proc. Natl. Acad. Sci. U.S.A.

108

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“…First, inhibition by amiloride is readily reversible (Bentley, 1968;Ehrlich and Crabbe, 1968) . Second, Na transport is enhanced beyond control levels after exposure of pretreated cells to control media when the cells have been pretreated with either amiloride-containing normal media or low-Na media (all solutions isotonic ; Ehrlich and Crabbe, 1968 ;Turnheim et al, 19'78) .…”

Section: Pump Stimulation During Volume Regulationmentioning

confidence: 99%

Volume-regulatory responses of Amphiuma red cells in anisotonic media. The effect of amiloride.

Siebens¹,

Kregenow²

1985

The Journal of General Physiology

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Amphiuma red cells were incubated for several hours in hypotonic or hypertonic media. They regulate their volume in both media by using ouabain-insensitive salt transport mechanisms . After initially enlarging osmotically, cells in hypotonic media return toward their original size by losing K, Cl, and H2O. During this volume-regulatory decrease (VRD) response, K loss results from a >10-fold increase in K efflux . Cells in hypertonic media initially shrink osmotically, but then return toward their original volume by gaining Na, Cl, and H2O. The volume-regulatory increase (VRI) response involves a large (>100-fold) increase in Na uptake that is entirely blocked by the diuretic amiloride (10-g M). Na transport in the VRI response shares many of the characteristics of amiloride-sensitive transport in epithelia: (a) amiloride inhibition is reversible ; (b) removal of amiloride from cells pretreated with amiloride enhances Na uptake relative to untreated controls ; (c) amiloride appears to act as a competitive inhibitor (K i = 1-3 AM) of Na uptake; (d) Na uptake is a saturable function of external Na (K m -29 mM); (e) Li can substitute for Na but K cannot . Anomalous Na/K pump behavior is observed in both the VRD and the VRI responses. In the VRD response, pump activity increases 3-fold despite a decrease in intracellular Na concentration, while in the VRI response, a 10-fold increase in pump activity is observed when only a doubling is predicted from increases in intracellular Na .

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“…It has also been used for studying the actions of diuretic drugs on the same phenomena (Ferguson, 1966;Bentley, 1968Bentley, , 1969Handler, Preston & Orloff, 1972;Ferguson & Smith, 1972).…”

Section: Introductionmentioning

confidence: 99%

Inhibition by diuretics of cyclic 3′,5′‐AMP‐dependent protein kinase from toad bladder epithelium

Ferguson

Twite

1973

British J Pharmacology

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Summary1. A cAMP-dependent protein kinase enzyme has been isolated from toad bladder epithelium.2. This enzyme catalyses the phosphorylation of histones; a reaction stimulated by 0'1 ,uM cAMP. 3. Activity of this enzyme in the presence of 0-1 umM cAMP was significantly inhibited by 100 ,mM mercuderamide, bumetanide and frusemide. A small, though statistically insignificant inhibition was seen with the same concentrations of hydrochlorothiazide and ethacrynic acid. 4. The half maximal inhibition was achieved with mercuderamide, 5 pmM, and with frusemide and bumetanide 600 ,uM.

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Amiloride: a potent inhibitor of sodium transport across the toad bladder

Cited by 387 publications

References 18 publications

Electrical currents through full-grown and maturing Xenopus oocytes.

Electrical currents through full-grown and maturing Xenopus oocytes.

Volume-regulatory responses of Amphiuma red cells in anisotonic media. The effect of amiloride.

Inhibition by diuretics of cyclic 3′,5′‐AMP‐dependent protein kinase from toad bladder epithelium

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