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H H Ussing

Publications and source records attributed to H H Ussing.

At least 19 recordsLinked to original sources
PubMed1996

Trapping of 134CS+ in frog skin epithelium as a function of short circuit current.

In the sodium/potassium pump of the isolated frog skin epithelium, 134CS+ can to a certain degree replace potassium. If 134CS+ in almost a carrier-free amount is added to the solution bathing the inside of the frog skin in an Ussing chamber, there will be an uptake of 134 CS+ into the epithelium cells which is proportional to the short circuit current. Transepithelial flux of 134CS+ in leaky epithelia, for instance small intestine and frog skin glands, indicates a paracellular pathway. The consequences of these findings for the recycling-theory are discussed.

Animals↗
PubMed1989

Mechanism of isotonic water transport in glands.

Since water and electrolytes pass cell membranes via separate channels, there can be no interactions in the membranes, and osmotic interactions between water and solutes can be expressed as the product of solute flux, frictional coefficient of solute, and length of pathway. It becomes clear that isotonic transport via a cell is impossible. In glands, where cation-selective junctions impede anion flux between the cells, isotonic water transport is only possible if sodium, after having passed the junction, is reabsorbed in the acinus and returned to the serosal side. Thus it can be recycled via the cation-selective junction and exert its drag on water more than once. This hypothesis was tested on frog skin glands. Skins were mounted in flux chambers with identical Ringer solutions on both sides. Na channels of the principal cells were closed with amiloride in the outside solution, and secretion stimulated with noradrenaline in the inside solution. Influx and efflux of Na, K and Br (used as tracer for Cl) were measured on paired half-skins during the constant-secretion phase. Flux ratios for both Na and K were higher than expected for electrodiffusion, indicating outgoing solvent drag. Flux ratios for K were much higher than those for Na. This is an agreement with the concept that Na is reabsorbed in the acinus and K is not. Two independent expressions for the degree of sodium recycling are developed. Under all experimental conditions these expressions give values for the recycling which are in good agreement.

Animals↗
PubMed1989

Transport pathways for Na+ and Br- (Cl-) in noradrenaline-stimulated frog skin (Rana temporaria).

(1) Transport pathways for Na+ and Br- across noradrenaline-stimulated frog skin, in which the sodium channels in the apical membrane had been blocked with amiloride, were examined by pre-steady-state flux ratio experiments. (2) To analyse the experiments, equations are derived from which the fluxes through two parallel pathways can be determined if these differ with respect to the flux ratio as well as the mean passage time for the ion in question. (3) The fluxes of Na+ and Cl- were followed over a period of 3 h and it was found that about 1 h after addition of noradrenaline time-invariant fluxes could be achieved. In that period inward and outward tracer fluxes of Na+ and Br- (used as a substitute for Cl-) were followed during the build-up of isotope in the tissue until steady-state fluxes were attained. (4) The experiments showed that when the Na channels of the capital cells are blocked the glands provide the major pathway for sodium transport across the skin. The efflux of Br- can be separated into two components. A fast one through the mitochondria-rich cells, which is the pathway for passive anion fluxes, and a slower one through the glands. No influx through the slow transport pathway could be detected. In some skins exchange of Br- through the mitochondria-rich cells is revealed. An anion exchange mechanism also appears to be present in the basolateral membrane of the gland cells.

Animals↗
PubMed1989

The effect of amiloride and benzimidazoleguanidine added to the inside medium on electrolyte pathways in the frog skin glands.

Serosal amiloride inhibits Na+, K+ and Cl- efflux and reduces short-circuit current and transepithelial conductance in noradrenaline-stimulated frog skin in which the sodium channels in the apical membrane are blocked by amiloride. BIG (benzimidazoleguanidine) inhibits Na+ and K+ efflux and reduces the short-circuit current. In some skins BIG decreased and in others it increased Cl- efflux and conductance. The variable response appears to be due not only to inhibition of salt extrusion from the gland cells but also to activation of Cl- transport through the mitochondria-rich cells, since it was shown that BIG could increase Cl- efflux in gland-free preparations. Different target mechanisms in the gland cells where the two substances may exert their effect are discussed.

Amiloride↗
PubMed1988

Odd behaviour of Li+ in frog skin ion transport.

1. Frog skin epithelium has basolateral K+ channels that normally define the basolateral membrane potential between 80 and 100 mV. 2. The membrane mentioned also has almost silent chloride channels and a [Na+, K+, 2Cl-] cotransport, the latter probably maintains the high Cl- in the capital (also called syncytium) cells. 3. If the K+ channels are blocked by Ba2+ (or Li+) it is possible to demonstrate potential gating of the chloride channels of the basolateral membrane. 4. When the normal K+ channels are blocked, a potential-dependent K+ conductance slowly emerges. 5. If Li+ is substituted for outside Na+ the skin shows potential oscillations of about 40 mV at a frequency of about six per hour. 6. The anion channel inhibitor Indacrinone stops these oscillations. 7. The role of Cl- and K+ channels in these oscillations is discussed. 8. The transepithelial inward transport of Li+ requires the presence of Na+ and seems to be due to exchange of cellular Li+ against inside Na+ via the basolateral Na+/H+ exchanger.

Animals↗
PubMed1987

Ion transport by mitochondria-rich cells in toad skin.

The optical sectioning video imaging technique was used for measurements of the volume of mitochondria-rich (m.r.) cells of the isolated epithelium of toad skin. Under short-circuit conditions, cell volume decreased by about 14% in response to bilateral exposure to Cl-free (gluconate substitution) solutions, apical exposure to a sodium-free solution, or to amiloride. Serosal exposure to ouabain resulted in a large increase in volume, which could be prevented either by the simultaneous application of amiloride in the apical solution or by the exposure of the epithelium to bilateral Cl-free solutions. Unilateral exposure to a Cl-free solution did not prevent ouabain-induced cell swelling. It is concluded that m.r. cells have an amiloride-blockable Na conductance in the apical membrane, a ouabain-sensitive Na pump in the basolateral membrane, and a passive Cl permeability in both membranes. From the initial rate of ouabain-induced cell volume increase the active Na current carried by a single m.r. cell was estimated to be 9.9 +/- 1.3 pA. Voltage clamping of the preparation in the physiological range of potentials (0 to -100 mV, serosa grounded) resulted in a cell volume increase with a time course similar to that of the stimulation of the voltage-dependent Cl conductance. Volume increase and conductance activation were prevented by exposure of the tissue to a Cl-free apical solution. The steady-state volume of the m.r. cells increased with the clamping voltage, and at -100 mV the volume was about 1.15 times that under short-circuit conditions. The rate of volume increase during current passage was significantly decreased by lowering the serosal K concentration (Ki) to 0.5 mM, but was independent of whether Ki was 2.4, 5, or 10 mM. This indicates that the K conductance of the serosal membrane becomes rate limiting for the uptake of KCl when Ki is significantly lower than its physiological value. It is concluded that the voltage-activated Cl currents flow through the m.r. cells and that swelling is caused by an uptake of Cl ions from the apical bath and K ions from the serosal bath. Bilateral exposure of the tissue to hypo- or hypertonic bathing solutions changed cell volume without detectable changes in the Cl conductance. The volume response to external osmotic perturbations followed that of an osmometer with an osmotically inactive volume of 21%.(ABSTRACT TRUNCATED AT 400 WORDS)

Amiloride↗
PubMed1986

Evidence from O2 uptake measurements for Na+ -K+ -2 Cl- co-transport in the rabbit submandibular gland.

There is evidence that the production of primary saliva by acinar cells is a consequence of Na+ -Cl- co-transport but more recently it has been proposed that in fact Na+ -K+ -2 Cl- co-transport is responsible. The latter would be energetically more efficient and the present experiments were designed to measure the stoichiometry of acinar secretion in order to distinguish between these two mechanisms. Submandibular salivary glands from anaesthetised rabbits were isolated vascularly and oxygen consumption measured from the oxygen content of arterial inflow and venous effluent blood and the total flow through the gland. Measurements were made in the steady-state at rest and during different secretion rates induced by parasympathetic nerve stimulation. The rate of sodium transport across the acinar and ductal epithelium was determined from plasma and salivary sodium concentration and salivary flow rate. Multiple regression analysis of this data showed that 22.1 mol Na+ was secreted per mol O2 consumed while 11.9 mol Na+ was reabsorbed per mol O2 consumed. Since acinar secretion is energetically about twice as efficient as ductal absorption, a mechanism for Na+ transport other than that for tight epithelia must be involved. Na+ -K+ -2 Cl- co-transport is thus more likely than Na+ -Cl- and it is suggested that Na+ -K+ -2 Cl- co-transport is the main mechanism involved in salivary acinar secretion.

Absorption↗
PubMed1986

Single-file diffusion through K+ channels in frog skin epithelium.

The ratio between the unidirectional fluxes of K+ across the frog skin with K-permeable outer membranes was determined in the absence of Na+ in the apical solutions. The experiments were performed under presteady-state conditions to be able to separate the flux ratio for K+ through the cells from contributions to the fluxes through extracellular leaks. The cellular flux ratio deviated strongly from the value calculated from the flux ratio for electrodiffusion. The experiments can be explained if the passive K transport through the epithelial cells proceeds through specific channels by single-file diffusion with a flux ratio exponent of about 2.5.

Animals↗
PubMed1986

Localization of chloride conductance to mitochondria-rich cells in frog skin epithelium.

Cell volume determinations and electrophysiological measurements have been made in an attempt to determine if mitochondria-rich (MR) cells are localized pathways for conductive movements of Cl across frog skin epithelium. Determinations of cell volume with video microscope techniques during transepithelial passage of current showed that most MR cells swell when the tissue is voltage clamped to serosa-positive voltages. Voltage-induced cell swelling was eliminated when Cl was removed from the mucosal bath solution. Using a modified vibrating probe technique, it was possible to electrically localize a conductance specifically to some MR cells in some tissues. These data are evidence supporting the idea that MR cells are pathways for conductive movements of Cl through frog skin epithelium.

Animals↗
PubMed1986

The volume of mitochondria-rich cells of frog skin epithelium.

The pathway for movement of chloride ions across frog skin is not well understood. Mitochondria-rich (MR) cells have been proposed as the route for chloride across the skin. To test this hypothesis we studied the MR cells of the skin of the frog, Rana pipiens, by quantitative light microscopic determination of cell volume. MR cell volume was influenced by changes in the chloride concentration or osmolality of the outside bathing solution. MR cells shrank about 23% when all chloride was removed from the outside (mucosal) bathing solution. MR cells were also shown to be responsive to changes in the osmolality of either the mucosal or serosal bath. Osmotically-induced swelling caused by dilution of the serosal bath resulted in volume regulatory decrease. These results are consistent with the hypothesis that MR cells constitute the pathway for chloride movement across frog skin.

Animals↗
PubMed1986

Epithelial cell volume regulation illustrated by experiments in frog skin.

The volume control of the syncytium of principal cells (as opposed to the mitochondria-rich cells) is largely confined to the movement of ions and water through the basolateral membrane. The apical membrane is nearly tight to water and ions except sodium. The basolateral membrane is normally tight to chloride, but its chloride channels open if the cells swell osmotically or if the membrane is depolarized. If the epithelium has lost KCl during osmotic swelling, it is recovered by a basolateral cotransport of KNaCl2.

Animals↗
PubMed1985

Volume regulation and basolateral co-transport of sodium, potassium, and chloride ions in frog skin epithelium.

Frog skin epithelium, which is normally almost tight to chloride, acquires a basolateral leakiness to chloride during osmotic swelling. By measuring the epithelial thickness (volume) after equilibration first with half thiocyanate Ringer, and then full thiocyanate Ringer, one obtains the chloride-free volume. Partial or full recovery of the volume and cellular chloride concentration occurs only when the inside of the skin is exposed to solutions containing K as well as Na and Cl. This recovery process is totally inhibited by low concentrations of bumetanide. The data suggest a basolateral NaKCl2 co-transport.

Animals↗
PubMed1985

Evaluation of transport pathways for Na+ across frog skin epithelium by means of presteady-state flux ratio.

A method is described that makes it possible to separate the sodium fluxes through the isolated frog skin into sets characteristic of the cellular and the paracellular pathway, respectively. If there are two significant pathways for the ion, and if they differ with respect to flux ratio as well as mean passage time, the flux ratios for the individual pathways can be obtained from a set of inward and outward tracer fluxes, covering the time from the addition of the tracers until the achievement of constant fluxes in both directions.

Animals↗
PubMed1985

Determination of the electromotive force of active sodium transport in frog skin epithelium (Rana temporaria) from presteady-state flux ratio experiments.

The presteady-state influxes and effluxes of sodium across frog skin epithelium have been determined as a function of time while all electrophysiological parameters were maintained constant. The fluxes measured were resolved in the fractions which have passed a pathway through the cells and those that have used a paracellular pathway. The procedure is based on the theory that all presteady-state flux ratios have to be equal to the steady-state flux ratio if only one pathway is involved. The flux ratios for the transcellular route were used to calculate the electromotive force of the sodium pump. The calculation hinges on the assumptions (a) that both influx and efflux have to pass through the sodium pump and (b) that single file diffusion of sodium is not taking place anywhere along the path. The validity of both assumptions is discussed. Our calculated values for the electromotive force of the sodium pump EaNa vary between 146 and 200 mV, which is in agreement with the energy of the ATP/ADP system. There is a distinct indication that, as the electrochemical gradient for sodium opposing the transport is being increased, the emf increases towards an asymptotic value around 200 mV. The relation between the value of EaNa and the cellular phosphorylation potential for ATP is discussed.

Animals↗
PubMed1982

Analysis of presteady-state Na+ fluxes across the rabbit corneal endothelium.

Instead of the conventional steady-state fluxes, the presteady-state fluxes of 22Na across the rabbit corneal endothelium were measured. In contrast to reports that there is no net Na+ movement across the corneal endothelium, we find a net transport of Na+ across this tissue. The direction of net Na+ flux is from the stromal to the aqueous side and the magnitude is 2.3 +/- 0.4 mueq/cm2 X hr (n = 11, SEM). Net Na+ transport is inhibited in the presence of ouabain (10(-4) M). Acetazolamide (10(-4) M) has only a slight inhibitory effect on the rate of Na+ transport but decreases the transendothelial potential difference by about 30%. The passive component of the Na+ transport has been estimated by analyzing the presteady-state influx and efflux curves and found to occur 10% via cellular and 90% via paracellular routes. The analysis for the separation of the pathways has been based on a recently proposed theory which holds that the flux ratio, regardless of its driving forces, is independent of time.

Acetazolamide↗
PubMed1982

Volume regulation of frog skin epithelium.

Previous results (MacRobbie & Ussing 1961) in combination with published values for cellular chloride concentration and for intracellular potentials show that the chloride concentration in frog skin epithelium cells is higher than predicted for equilibrium with the inside bathing solution. Both the apical and the basolateral membrane of these cells are normally almost tight to chloride, so that the maintenance of the high chloride concentration requires little work. A basolateral permeability to chloride is, however, activated by cell swelling, and the cells lose KCl. It is now shown that the KCl thus lost cannot be regained neither in the absence of sodium in the inside bath nor in the presence of furosemide. The volume regulation reactions are, however, independent of the composition of the outside bath. It is concluded that the recovery of KCl by the epithelium is due to a basolateral co-transport of NaCl from medium to cells, combined with return of Na to the medium via the Na-K pump. The co-transport mechanism thus restores the high chloride concentration of the cells, but seems to be virtually dormant unless the cells have lost chloride.

Animals↗