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E Frömter

Publications and source records attributed to E Frömter.

At least 73 records · Page 4Linked to original sources
PubMed1989

A method to quantify and correct for edge leaks in Ussing chambers.

A technique is presented which allows edge leaks in Ussing chambers to be detected and quantified. It is based on the fact that in leaky chambers direct current or low frequency alternating current passes preferentially around the edge of the tissue, while high frequency alternating current shunts the cell membranes and distributes homogeneously through the entire chamber. By measuring the current density in the center of the chamber with low and high frequency alternating current and using correction factors which account for the shape of the electrical field as a function of chamber geometry and of estimated tissue resistance, edge leaks can be quantified. This technique allows correct transepithelial resistance values to be obtained from leaky measurements, and enables the question of whether a given discrepancy between cellular and transepithelial resistances reflects leaky tight junctions or a leaky chamber or both to be answered.

Animals↗
PubMed1989

A new double-barrelled, ionophore-based microelectrode for chloride ions.

A new Cl- selective microelectrode based on the ionophore 5,10,15,20-tetraphenyl-21H,23H-porphin manganese(III) chloride is presented which discriminates better against HCO3- and several organic anions than electrodes containing the Corning 477913 ion-exchanger. Using a redesigned construction procedure, fine-tip double-barrelled microelectrodes were produced which had slopes of -52.4 +/- 0.6 mV (SE, n = 24), resistances of about 7.10(11) omega and a selectivity coefficient log KpotCLHCO3 of -1.40 +/- 0.03. Some electrodes showed a small unexplained sensitivity to pH greater than 7.6. When used to puncture cells of isolated S3 segments of rabbit renal proximal tubule during perfusion with HCO3- Ringer solution, the electrodes gave a membrane potential of -69.8 +/- 1.5 mV and an intracellular Cl- activity, [Cl-]i, of 35.3 +/- 2.6 mmol/l. Upon switching bath and lumen perfusions to Cl- -free solutions the "residual" [Cl-]i dropped to 1.20 +/- 0.03 mmol/l, while in similar measurements with ion-exchanger electrodes the "residual" [Cl-]i dropped only to 10.9 +/- 0.5 mmol/l. These observations demonstrate the superiority of the new electrode and prove that previously determined high [Cl-]i values in Cl- -free ambient solutions reflect interference problems rather than non-exchangeable intracellular chloride.

Animals↗
PubMed1989

Selective expression of an amiloride-inhibitable Na+ conductance from mRNA of respiratory epithelium in Xenopus laevis oocytes.

Poly(A)+RNA was prepared from primary cultures of human nasal polyp epithelia and from native bovine tracheal epithelia. Six to fifty nanograms mRNA were injected into prophase-arrested immature Xenopus laevis oocytes. One to four days later the oocytes were probed with electrophysiological techniques for induction of novel ion conductances. Oocytes injected with mRNA had lower membrane potentials (Vm) and resistances (Rm) than controls. By use of step changes in extracellular Na+ concentration and applying amiloride, a Na+ conductance could be identified in mRNA-injected oocytes, which was inhibited by submicromolar concentrations of amiloride with the same kinetics (Ki = 1.3 X 10(-7) mol/l) as in the original tissue. After complete inhibition of this conductance by 10(-5) mol/l amiloride, Vm and Rm approached the respective values of controls. The data indicate that oocytes express functional epithelial Na+ channels but apparently no other epithelial ion conductances from injected mRNA of respiratory epithelium.

Amiloride↗
PubMed1988

Mechanisms of basolateral base transport in the renal proximal tubule.

Renal proximal tubules absorb HCO3- by secretion of H+ into the tubular lumen. This paper focuses on the mechanisms of HCO3- exit across the basolateral cell membrane. The major exit pathway is rheogenic sodium bicarbonate co-transport. This system transports Na+ and HCO3-, but not Cl-, in obligatory coupling at a fixed overall stoichiometry of three HCO3- to one Na+. The fact that HCO3- flux is reduced after inhibition of cytoplasmic and/or membrane-bound peritubular carbonic anhydrase indicates that HCO3- is not transported as such but is split during permeation into its buffer subspecies from which it is regenerated on the other side of the membrane. Since flow of OH- or of H+ (in opposite directions) can be excluded, it appears most likely that one HCO3- and one CO3(2-) move together with one Na+. Besides carbonic anhydrase inhibitors, disulphonic stilbenes and harmaline are known to block the co-transporter. In addition to rheogenic Na+ (HCO3-)3 co-transport, Na+-dependent and Na+-independent electroneutral Cl-/HCO-3 exchange have been identified. The latter mechanisms are particularly important in S3 segments of proximal tubule where Na+ (HCO3-)3 co-transport is missing. Further mechanisms which operate in parallel, but at lower rates, are electroneutral SO4(2-)/HCO3- exchange and, in some species, lactate/HCO3- exchange. Moreover, there may be some uncoupled OH- flux and it is reasonable to assume that OH- (or H+) flux is involved in the transport of dicarboxylic acids across the basolateral cell membrane.

Animals↗
PubMed1988

Influence of lateral intercellular spaces on current propagation in tubular epithelia as estimated by a multi-cable model.

A multiple cable model has been developed for tubular epithelia which allows current flow along the tubular lumen, along the cell layer and inside the lateral intercellular space (LIS) to be quantitatively assessed. In this model tubular lumen and cell layer are represented by two concentric cylinders and the LIS by n concentric interconnected fluid layers which are interposed between the cells, contact the lateral cell membranes and extend all along the tubular length. The innermost LIS layer connects to the tight junctions and the outermost layer to the peritubular space. Modelling each element by a cable-like structure the mathematical solution leads to n + 2 linear combinations of n + 2 exponential functions. Based on morphometric data and resistance measurements on Necturus proximal tubule [4,10] model calculations have been performed of the voltage attenuation along tubular lumen, cell layer and LIS for n = 3 or n = 6 assuming different LIS widths (0.02, 0.2, and 2.0 micron). The results show that the influence of LIS is insignificant in Necturus proximal tubule under control conditions, but may become significant in other functional states or other tubules. Collapsing the LIS increases predominantly the shunt resistance and the effective resistance of the lateral cell membrane but longitudinal current propagation along the LIS remains negligible at all space widths. In addition, model calculations are presented which allow errors in determining tight junction resistance and cell membrane resistances from a simple cable model to be quantified as function of LIS width.

Animals↗
PubMed1988

Ionic conductances of cultured principal cell epithelium of renal collecting duct.

The ionic conductive properties were studied of epithelia of collecting duct principal cells which had been grown in primary tissue culture from renal cortex/capsule explants. When pretreated with aldosterone (10(-6) mol/l) and bathed on either surface with isotonic HCO3(-)-free Ringer's solution, the transepithelial voltage, Vte, varied between -21 and -72 mV (apical surface negative) while the transepithelial resistance, Rte, ranged from 0.4 to 1.5 k omega cm2. By 10:1 step-changes in Na+ concentration the apical cell membrane was shown to have a high conductivity for sodium, inhibitable by amiloride, 10(-6) mol/l. However, contrary to observations in natural collecting duct under control conditions, amiloride never reversed the polarity of Vte even at 10(-4) mol/l. Both the apical and the basolateral cell membranes were conductive for potassium and both conductivities were inhibitable by Ba2+ (5 mmol/l). 10:1 reduction of apical Cl- concentration strongly hyperpolarized Vte with a monophasic time course suggesting the presence of a paracellular shunt conductance for Cl-. In addition there may be a small Cl- conductance present in the apical cell membrane since apical application of the chloride channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPAB) at 10(-7) mol/l produced a minute but significant hyperpolarization. On the other hand, 10:1 reduction of basolateral Cl- concentration caused a biphasic change in Vte (initial depolarization, followed by repolarization) which indicates the presence of a large Cl- conductance in the basolateral cell membrane. The latter was not inhibitable by 10(-7) mol/l NPPAB. Higher concentrations of this and of an other Cl-channel blocker produced non-specific effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Mechanisms and regulation of ion transport in the renal collecting duct.

1. In the present paper the ion transport function of the renal mammalian collecting duct and its regulation is briefly reviewed. 2. The epithelium is characterized by different cell types: principal cells, intercalated cells, type A, and intercalated cells, type B. 3. Using microelectrodes and various microscopic techniques active Na+ absorption as well as K+ secretion has been localized to the principal cells, while Cl- absorption was found to proceed largely, though not exclusively, through the tight junctions between cells. 4. Intercalated cells of type A, which prevail in the outer medullary collecting duct, secrete H+ and intercalated cells of type B, which are most frequent in the late cortical collecting duct, secrete HCO3-. 5. This specialization of different cells in transporting individual ions provides the basis for the efficient adaptive regulation of urinary ion excretion.

Animals↗
PubMed1987

Evidence for OH-/H+ permeation across the peritubular cell membrane of rat renal proximal tubule in HCO3(-)-free solutions.

Membrane potentials and intracellular pH were measured on rat renal proximal tubular cells in vivo to test whether sodium-bicarbonate cotransport across the peritubular cell membrane accepts OH- (or H+ in opposite direction) or whether it requires the CO2, HCO3-, CO3= buffer to operate. It was found that step changes of peritubular pH in nominally HCO3(-)-free and CO2-free solutions produced qualitatively similar initial potential responses and cell pH responses as changes in peritubular HCO3- concentrations. These responses, however, were considerably smaller and they were neither reduced in Na+-free solutions nor inhibited by the stilbene derivative SITS which is known to block Na+ (HCO3-)n cotransport completely. We conclude that the cotransporter requires the CO2, HCO3-, CO3= buffer for its physiological operation but that high rates of OH- or H+ can also be transferred across the peritubular cell membrane in HCO3(-)-free solutions, probably through a separate transport system.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1987

Evidence for rheogenic sodium bicarbonate cotransport in the basolateral membrane of oxyntic cells of frog gastric fundus.

Ionic conductance properties of the basolateral cell membrane of oxyntic cells were studied in frog gastric fundus in vitro. After mounting the fundus in a modified Ussing chamber the serosal connective tissue was dissected off and individual oxyntic cells were punctured from the serosal surface with microelectrodes. Under resting conditions the membrane potential averaged -56.9, SD +/- 9.5 mV (n = 63), cytoplasm negative. Lowering or raising serosal HCO-3 concentration from 17.8 to 6 or 36 mmol/l respectively at constant PCO2 depolarized or hyperpolarized the cell membrane by +16.7 or -18.2 mV respectively. Sudden removal of serosal Na+ also depolarized the cell membrane (anomalous Nernst response). Since both the HCO-3 dependent and the Na+ dependent potential changes were strongly depressed by the disulfonic stilbene SITS and since the potential response to HCO-3 was virtually abolished in Na+-free solution we conclude that a rheogenic Na+ (HCO-3)n-cotransport system (n greater than 1) is present in the basolateral cell membrane of oxyntic cells. Its possible role in base transfer during HCl-secretion or HCO-3 secretion remains to be elucidated.

Animals↗
PubMed1987

Characterization of human sweat duct chloride conductance by chloride channel blockers.

To characterize the chloride conductance of human sweat duct the effect of various analogues of diphenylamine-2-carboxylate was investigated on the transepithelial potential difference (PDT) and resistance (RT) of isolated microperfused sweat ducts. Although the most powerful analogues which block Cl- channels in various secretory and absorptive epithelia were ineffective, a number of analogues (in particular Cl substituted ones) were found which at high concentrations significantly and reversibly increased PDT and RT. The data suggest that the main chloride conductance pathway of sweat duct epithelium resides in the cell membranes rather than in the tight junctions. In addition the different blocking spectra of the chloride conductances of sweat duct and tracheal epithelium (Welsh MJ, Science 232:1648, 1986) suggest that the combined impairment of both conductances in cystic fibrosis does not result from a molecular defect in the Cl- channels.

Chlorides↗
PubMed1987

Axial heterogeneity of sodium-bicarbonate cotransport in proximal straight tubule of rabbit kidney.

Intracellular microelectrodes were used to investigate rheogenic Na+ (HCO3-)n cotransport in different segments of isolated proximal straight tubule (PST) of rabbit kidney. In the first portion (S2 segment) the peritubular cell membrane potential Vb averaged -46.0, SE +/- 1.3 mV (n = 20), while in terminal portion (S3 segment) it averaged -68.3, SE +/- 2.5 mV (n = 10). This difference may reflect different modes of anion permeation across the peritubular cell membrane. In S2 segments, sudden 10:1 reduction of bath HCO3- concentration caused a fast transient cell depolarization, delta Vb = -45.8, SE +/- 1.2 mV (n = 33) as expected from the presence of Na+ (HCO3-)n cotransport. As the puncture site moved further distally, delta Vb declined and gradually changed its time course by superposition of a slower secondary depolarization. In this region the transient cell depolarization could be recuperated by inhibiting the peritubular K+ conductance with Ba2+ (1 mmol/l). In S3 segments, however, the HCO3(-)-dependent transient cell depolarization was completely lost both in the absence and presence of Ba2+. In addition, sudden reduction of bath Na+ concentration did not acidify the cell, as it did in the S2 segment. The data indicate that the expression of Na+ (HCO3-)n cotransport in the peritubular cell membrane gradually diminishes towards the end of the S2 segment and is lost in the S3 segment.

Barium↗
PubMed1987

High-conductance K+ channel in apical membranes of principal cells cultured from rabbit renal cortical collecting duct anlagen.

Using the patch clamp technique, one type of K+ channel was identified in the apical cell membrane of cultured principal cells of rabbit renal collecting ducts in the cell-attached or excised-patch configuration. The channel was highly selective for K+ over Na+ (typically 30-70-fold) and had a conductance of 180, SD +/- 39 pS (n = 6), referred to a situation of 140 mmolar K+-Ringer solution present on either surface of the patch membrane. Channel activity was completely blocked by Ba2+ (5 mmol/l) and partially inhibited by Na+. The latter was evidenced by a deviation from Goldman rectification at high cytoplasm-positive membrane potentials, which was observed when Na+ competed with K+ for channel entrance from the cytoplasmic surface. Channel open probability depended strongly on membrane voltage and cytoplasmic Ca2+ concentration. Open-close kinetics exhibited double exponential behaviour, with a strong voltage dependence of the slow open time constant. Infrequently also a substate conductance level was identified. The voltage and calcium dependence suggest that the channel plays a role in adjusting K+ secretion to Na+ absorption in the fine regulation of cation excretion in renal collecting ducts.

Animals↗
PubMed1986

Direct demonstration of high transepithelial chloride-conductance in normal human sweat duct which is absent in cystic fibrosis.

The transepithelial electrical potential difference (Vt) and the transepithelial resistance (Rt) were measured across individual microdissected sweat ducts obtained from biopsies of the scapular region of normal human volunteers and of a Cystic Fibrosis (CF) patient. During luminal and contraluminal perfusion with NaCl Ringer solution Vt and Rt were -10.7 +/- 1.1 (mV, lumen negative) and 10.9 +/- 1.7 (omega X cm2). Bilateral substitution of Cl- by gluconate increased Vt and Rt to -42.7 +/- 5.1 (mV) and 98.0 +/- 12.0 (omega X cm2), respectively. Luminal application of amiloride (10(-4) mol/l) collapsed Vt and increased Rt to 11.4 +/- 1.7 and 159.7 +/- 12.0 omega X cm2 in Cl- and gluconate Ringer respectively. These data indicate that 90% of the total transepithelial conductance is attributed to Cl- and 5% to Na+ while the remaining 5% is unaccounted for at present. In CF ducts Vt and Rt were high already in Cl- Ringer solution (-78.9 +/- 9.9 mV and 91.2 +/- 15.6 omega X cm2) and did not change significantly after replacement of Cl- by gluconate. The data demonstrate that normal human sweat duct epithelium, despite its ability to generate high electric and osmotic gradients, is a low resistance epithelium, probably because of a high Cl(-)-permeability of its cell membranes. In addition, the data demonstrate that this Cl(-)-conductance is missing in CF, in conformation of what has been postulated previously from simple potential measurements.

Adult↗
PubMed1986

Histamine reduces Cl- activity in surface epithelial cells of frog gastric mucosa. Suggestive evidence for ionic coupling between surface epithelial and oxyntic cells.

Intracellular chloride activity (acCl) and serosal as well as mucosal membrane potentials (Vcs and Vcm) were recorded in surface epithelial cells (SEC) of frog gastric mucosa during the resting state (cimetidine, 10(-4) mol/l) or during stimulation with histamine (10(-4) mol/l). Stimulation leads to a fall in acCl from 18.7 SD +/- 5.9 mmol/l (n = 26) to 13.3 SD +/- 4.9 mmol/l (n = 33). Simultaneously both cell membranes hyperpolarize, Vcs from -56.0 SD +/- 4.8 (n = 42) to -62.8 +/- 7.6 (n = 43) and Vcm from -39.6 SD +/- 5.8 (n = 42) to -47.9 +/- 7.6 (n = 43), so that intracellular chloride remains elevated above electrochemical equilibrium at both cell membranes. Reduction or omission of chloride in the lumen perfusate does not affect acCl, suggesting that the luminal cell membrane is virtually tight for chloride ions. Current induced hyperpolarization of the serosal cell membrane potential which simulates the electrical effects of stimulation, does not affect acCl either; however, inhibition of gastric acid secretion by a benzimidazol derivative which is known to block the H+/K+ ATPase prevents the fall in acCl in response to histamine. The same holds if the experimental solutions are gassed with 25% CO2 which does not interfere with acid secretion but may block cell to cell communication via gap junctions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Electrical properties of renal collecting duct principal cell epithelium in tissue culture.

Whereas collecting duct epithelium in vivo is composed of principal and intercalated cells, we grew a pure principal cell epithelium using a new technique involving tissue culture. These principal cells were derived from collecting duct anlagen of newborn rabbits. We investigated the electrical properties of such epithelia in a newly designed lucite double-chamber with an inner opening of 0.08 cm2. Our observations were: mean transepithelial resistance Rte was 0.83 +/- 0.2 k omega cm2 at 37 degrees C and after preincubation in aldosterone; mean transepithelial potential difference Vte was low and variable under standard conditions and at room temperature but increased to -59.5 +/- 4.4 mV (sign referring to polarity of apical surface) after preincubation in 10(-6) mol/l aldosterone and at 37 degrees C; 10(-6) mol/l amiloride added to the apical perfusion fluid largely abolished this Vte while increasing Rte by 120%; experiments with 5 X 10(-3) mol/l BaCl2 in the apical perfusion fluid failed to change Rte and Vte significantly. This principal cell epithelium therefore has characteristics of a "tight" epithelium with active sodium transport; however, its electrical properties differ from those of the isolated perfused collecting duct segment.

Aldosterone↗