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Biomedical subjects

T U Biber

Publications and source records attributed to T U Biber.

At least 37 records · Page 2Linked to original sources
PubMed1980

Influence of extracellular Cl concentration on Cl transport across isolated skin or Rana pipiens.

The effect of changes in Cl concentration in the external and/or serosal bath on Cl transport across short-circuited frog skin was studied by measurements of transepithelial Cl influx (J13Cl) and efflux (J31Cl), short-circuit current, transepithelial potential, and conductance (Gm). J14Cl as well as J31Cl were found to have a saturating component and a component which is apparently linear with Cl concentration. The linear component of J31Cl appears only upon addition of Cl to external medium, and about 3/4 of this component does not contribute to Gm. The saturating component of J31Cl is only 5% of total J31Cl with 115mM Cl in the serosal medium. Replacement of 115 mM Cl- in external medium by SO4=, NO3-, HCO3- or I- results in 87-97% reduction of J31Cl, whereas replacement with Br- has no effect. As external Cl concentration is raised in steps from 2 to 115 mM, J13Cl and J31Cl increase by the same amount but J13Cl is persistently 0.15 mueg/cm2hr larger than J31Cl. These results indicate that at least 3/4 of linear components of J13Cl and J31Cl proceed via an exchange diffusion mechanism which seems to be located at the outer cell border. The saturating component of J13Cl is involved in active Cl transport in an inward direction, and there is evidence suggesting that Cl uptake across outer cell border, which proceeds against an electrochemical gradient, is electroneutral but not directly linked to Na.

Animals↗
PubMed1980

Influence of extracellular Cl concentration on Cl transport across isolated skin of Rana pipiens.

The effect of changes in Cl concentration in the external and/or serosal bath on Cl transport across short-circuited frog skin was studied by measurements of transepithelial Cl influx (JCl13) and efflux (JCl31), short-circuit current, transepithelial potential, and conductance (Gm). JCl13 as well as JCl31 were found to have a saturating component and a component which is apparently linear with Cl concentration. The linear component of JCl31 appears only upon addition of Cl to external medium, and about 3/4 of this component does not contribute to Gm. The saturating component of JCl31 is only 5% of total JCl31 with 115 mM Cl in the serosal medium. Replacement of 115 mM Cl- in external medium by SO4=, NO3-, HCO-3 or I- results in 87-97% reduction of JCl31, whereas replacement with Br- has no effect. As external Cl concentration is raised in steps from 2 to 115 mM, JCl13 and JCl31 increase by the same amount but JCl13 is persistently 0.15 mu eq/cm2hr larger than JCl31. These results indicate that at least 3/4 of linear components of JCl13 and JCl31 proceed via an exchange diffusion mechanism which seems to be located at the outer cell border. The saturating component of JCl13 is involved in active Cl transport in an inward direction, and there is evidence suggesting that Cl uptake across outer cell border, which proceeds against an electrochemical gradient, is electroneutral but not directly linked to Na.

Animals↗
PubMed1980

Effect of external cation and anion substitutions on sodium transport in isolated frog skin.

Effects of changes in external ionic strength, external cation and/or anion substitution on transepithelial influx and efflux of sodium, short-circuit current and on transepithelial potential difference and resistance were studied in isolated frog skin. Active transport of Na was found to be highly dependent on both anionic and cationic composition of external medium. Relative abilities of external monovalent cations to inhibit active Na transport were H greater than Li greater than K greater than Rb greater than Cs greater than choline. Relative abilities of external monovalent anions to stimulate active Na transport were I greater than Br greater than Cl. Sequences of anion interaction and of resistance changes suggest that anionic stimulation of Na transport is not due to electrical coupling across outer cell membrane. The ability of different anions and cations to alter Na transport suggests that externally located charged groups act as important barriers or filters to ion movement. In addition, the experiments suggest that an increase in ionic strength of external medium has an effect on active transport of Na, a finding that indicates interference of surface charges with Na entry. Directional changes in efflux of Na due to changes in ionic composition of external medium usually paralleled changes in active Na transport. It is possible that the observed relationship between influx and efflux of Na is the result of common pathways and of interaction of the active transport system with Na efflux.

Animals↗
PubMed1977

Effect of inhibitors on transepithelial efflux of Na and nonelectrolytes in frog skin.

The transepithelial efflux of Na and several nonelectrolytes (mannitol, sucrose, and polyethylene glycol 900) were measured in the isolated frog skin under short-circuited conditions in chambers that had been specially designed to avoid edge damage. Ouabain (10(-3) and 10(-4) M) caused a dramatic increase in the efflux of Na, whereas the efflux of nonelectrolytes showed only a slight alteration. The efflux of Na increased after the application of dinitrophenol (10(-4) M), whereas the efflux of nonelectrolytes remained constant. Amiloride (10(-3) M) caused large variations in the efflux of Na, whereas the efflux of nonelectrolytes remained unchanged. The results provide evidence that these inhibitors do not alter the permeability of the paracellular pathway and that the total transepithelial efflux of Na or at least a very large portion of it, and possibly also the transepithelial efflux of Cl, proceeds via a transcellular pathway and not a paracellular pathway as has been widely accepted. The data further suggest that the Na proceeding via this pathway interacts directly or indirectly with the active transport step.

Amiloride↗
PubMed1976

Ion transport and structure of urinary bladder epithelium of Amphiuma.

The urinary bladder of Amphiuma exhibits stable transport properties and an electrical potential difference in vitro. The lumen is significantly negative to the serosa and under short-circuited conditions flux rations for Na and Cl of 5.92 +/- 0.42 and 1.81 +/- 0.20, respectively, were observed. The close agreement between the short-circuit current and net Na flux suggests that most, if not all, of the current is carried by Na. Both ouabain and amiloride decreased the short-circuit current and the mucosal-to-serosal (M leads to S) flux of Na. Furosemide caused a transient increase in the M leads to S flux of Na and Cl but ADH was without effect. In bladders that had high transmural resistance, a net movement of K in the M leads to S direction under short-circuited conditions with flux ratios of up to 2 could be observed. The epithelium of the Amphiuma bladder consists of three cell types: granular cells, basal cells, and mitochondria-rich cells. No goblet cells are present. The mitochondria-rich cells comprise less than 5% of the population of the surface epithelium in Amphiuma in contrast to other amphibian bladders, where it accounts for up to 25% of the population.

Amiloride↗
PubMed1976

Saturation kinetics of sodium efflux across isolated frog skin.

Measurement of Na efflux across the frog skin epithelium from the serosal side to the outside (JNa 3 leads to 1) in a new chamber specifically designed to avoid edge damage shows that JNa 3 leads to 1 exhibits saturation kinetics with a maximal efflux (Jmax) of 31.8 nmol/cm2 per h and an apparent KNa of 4.0 mM. In contrast, JNa 3 leads to 1 measured in conventional chambers and efflux determinations in the new chamber of substances that pass the epithelium via extracellular pathways (polyethylene glycol 900, sucrose, mannitol) exhibit a linear relationship between the efflux of the substance in question and its concentration in the bath. In addition, changes in external Na concentration do not cause substantial changes in JNa 3 leads to 1. The saturation remains but both Jmax and KNa increase after application of ouabain. Amiloride, as well as dinitrophenol, eliminates the saturation and JNa 3 leads to 1 becomes a linear function of Na concentration. The separate effects of ouabain and amiloride suggest that these two inhibitors which are known to affect two distinctly different steps in the active transport pathway act also on two separate steps of JNa 3 leads to 1: the passage across the inward- (serosal) and outward-facing (apical) cell membranes of the epithelial cells, respectively. The action of dinitrophenol indicates the involvement of metabolism in JNa 3 leads to 1 probably at the latter of the two steps. The results suggest strongly that JNa 3 leads to 1 proceeds not via a paracellular but via a transcellular pathway that interacts with the active transport pathway.

Action Potentials↗
PubMed1976

Transepithelial transport kinetics and Na entry in frog skin: effects of novobiocin.

Na+ entry across the outer surface of frog skin and transepithelial Na transport were studied simultaneously at different [Na] in either the presence or absence of novobiocin by direct measurements of J12 (unidirectional uptake) and Io (short-circuit current). J12 consisted of two components: one linear, the other saturable. The kinetic parameters of the saturating components in controls were close to the kinetic parameters of overall transepithelial transport (Jm12 = 1.68+/-0.13 mleq cm-2h-1; Io =1.80+/-0.14 mueq cm-2h-1. K12 = 6.02+/-1.27 mM;Kio=6.12+/-1.33 mM). Novobiocin significantly augmented net transepithelial Na transport by increasing J13. J31 remained unaffected. A 1:1 relationship between the saturating component of J12 and Io was observed in both treated and untreated skins at all [Na] tested. (Jm12Iom, k12, and Kio were significantly larger in treated skins, but despite very drastic changes in transport rates, a close correlation between kinetic parameters of entry step and transepithelial transport was maintained. This suggests that the kinetics of transepithelial transport may simply reflect those of the rate-limiting step: the Na entry across the outer barrier of the skin. The results indicate that the linear component of J12 is not involved in transepithelial transport kinetics.

Animals↗
PubMed1973

Influence of transepithelial potential difference on the sodium uptake at the outer surface of the isolated frog skin.

The unidirectional uptake of sodium across the outer surface of the isolated frog skin (J(12) (Na)) was measured in the presence of transepithelial potential difference (Delta(psi)) ranging from +100 to -100 mV. With a sodium concentration of 115 mM in the bathing solutions J(12) (Na) increases significantly when the spontaneous Delta(psi) is reduced to zero by short-circuiting the skin. With an Na concentration of 6 mM a progressive increase J(12) (Na) can be observed when Delta(psi) is decreased in several steps from +100 to -100 mV (serosal side positive and negative, respectively). The observed change J(12) (Na) amounts to a fraction only of that predicted from the shift in Delta(psi). The results suggest that under open circuit conditions the potential step across the outside surface is at most one half of Delta(psi) and that the resistance across the outside and inside barrier of the skin is ohmic. This is in agreement with measurements of intracellular potentials in the frog skin and with resistance measurements carried out in the toad skin. The data strongly support the view that the saturating component of J(psi) proceeds via a charged carrier system. Exposure to negative values of Delta(psi) of 50 mV or more for times of 24 min or more result in a marked reduction of J(12) (Na) which shows only partial or no reversibility.

Amiloride↗
PubMed1971

Effect of changes in transepithelial transport on the uptake of sodium across the outer surface of the frog skin.

The unidirectional sodium, uptake at the outer surface of the frog skin was measured by the method described by Biber and Curran (8). With bathing solutions containing 6 mM NaCl there is a good correlation between sodium uptake and short-circuit current (SCC) measured simultaneously except that the average uptake is about 40% higher than the average SCC. The discrepancy between uptake and SCC increases approximately in proportion to an increase in sodium concentration of the bathing solutions. Amiloride inhibits the unidirectional sodium uptake by 21 and 69% at a sodium concentration of 115 and 6 mM, respectively. This indicates that amiloride acts on the entry step of sodium but additional effects cannot be excluded. The sodium, uptake is not affected by 10(-4)M ouabain at a sodium concentration of 115 mM but is inhibited by 40% at a sodium concentration of 6 mM. Replacement of air by nitrogen leads to a 40% decrease of sodium uptake at a sodium concentration of 6 mM. The results support the view proposed previously (8) that the sodium uptake is made up of two components, a linear component which is, essentially, not involved in transepithelial movement of sodium and a saturating component which reflects changes in transepithelial transport. Amiloride, seems largely to affect the saturating component.

Amidines↗
PubMed1970

Direct measurement of uptake of sodium at the outer surface of the frog skin.

A combination of the methods described by Schultz et al. (6) and by Ussing and Zerahn (9) was used to measure directly the unidirectional uptake of sodium from the outside solution into the frog skin, under short-circuit conditions. The sodium uptake was determined at six sodium concentrations ranging from 3.4 to 114 mM. NaCl was replaced by choline chloride in the solutions bathing both sides of the skin. Sodium uptake is not a linear function of sodium concentration but appears to be composed of two components, a saturating one and one that varies linearly with concentration. The sodium uptake is inhibited by the addition of lithium to the outside solution. The effect appears to be primarily on the saturating component and has the characteristics of competitive inhibition. In addition, lithium uptake by the skin is inhibited by sodium. The effects of lithium cannot be ascribed to changes in electrical potential difference. Measurements with microelectrodes indicate that under short-circuit condition there is no change in the intracellular potential when lithium chloride is added to the outside solution.

Animals↗
PubMed1969

Studies on the role of angiotensin in experimental renovascular hypertension: an immunologic approach.

The role of angiotensin in three forms of experimental hypertension was assessed in rats. First, the acute blood pressure response to injected angiotensin amide and angiotensin acid was determined. Rats made hypertensive with deoxycorticosterone and saline showed exaggerated responses; rats made hypertensive by clipping one renal artery showed depressed responses; and rats made hypertensive by clipping one renal artery and contralateral nephrectomy showed normal responsivity to angiotensin amide but depressed responsivity to angiotensin acid. These findings suggested that different mechanisms may be involved in the three types of hypertension studied. To assess the role of angiotensin in these hypertensive rats the blood pressure response, the presence of antibodies determined by radioimmune techniques, and the degree of refractoriness to injected angiotensin after immunization with angiotensin were studied. None of six rats made hypertensive by deoxycorticosterone and saline, and none of five mock immunized rats with renal hypertension of both types had a fall in blood pressure. By contrast, of the 20 rats with both types of renal hypertension in which antibody determinations were made, 11 had developed a significant antibody titer, of which seven showed a significant reduction in blood pressure at the time of antibody determination, and three of the remaining four had a significant blood pressure reduction earlier in their course. None of the nine renal hypertensive rats without demonstrable antibodies had a reduced blood pressure at the time of antibody determination, and only one had an earlier reduction in blood pressure. The renal hypertensive rats were all refractory to injected angiotensin after immunization. These results suggest a primary role for angiotensin in both forms of renal hypertension.

Angiotensin II↗
PubMed1968

Coupled solute fluxes in toad skin.

Net inward flux of mannitol across toad skin induced by making the outside solution hypertonic with urea has been investigated. No significant relation between net mannitol flux and net Na flux could be detected when both fluxes were measured simultaneously. In addition, the net mannitol flux caused by hypertonic solution was not altered by inhibition of Na transport with ouabain or by replacement of all Na in the bathing solutions by choline. The rate of net mannitol flux was dependent on the magnitude of the urea concentration difference across the skin and the direction of net flux could be reversed by reversing the direction of the urea concentration difference. These observations suggest that the mannitol transfer is the result of a coupling between the flows of urea and mannitol.

Animals↗