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T Anagnostopoulos

Publications and source records attributed to T Anagnostopoulos.

At least 55 records · Page 3Linked to original sources
PubMed1982

The electrical profile of the distal tubule in Triturus kidney.

The transepithelial potential difference (VTE) and transepithelial resistance (RTE) were determined along the length of the distal tubule of the amphibian Triturus alpestris. The site of impalements was determined at the end of each experiment by latex injection and microdissection. Two segments, differing by their distribution at the surface of the kidney, by their respective diameters and by their electrical properties could be identified: the early distal tubule (EDT) and the late distal tubule (LDT). VTE was invariably positive in the EDT; it increased from approximately + 5 mV to approximately + 22 mV within the first 30% of this segment and remained roughly constant distally to this site. RTE was estimated at 57 omega X cm2 in the EDT. The LDT exhibited essentially negative VTE figures with the exception of its very initial portion; the peak negativity at the end of the LDT was -35 mV. RTE was assessed from 8 measurements performed in the first 30% of the LDT; the tentative transepithelial resistance was 530 omega X cm2. Provisional evidence suggests that the transepithelial resistance of the terminal portion of the LDT may be substantially larger than the resistance measured in other parts of this segment.

Animals↗
PubMed1982

Proximal cell K+ activity: technical problems and dependence on plasma K+ concentration.

UNLABELLED: K+-selective liquid ion-exchanger double-barreled microelectrodes were used to measure intracellular K+ activity (alpha Ki) of proximal tubular cells in Necturus kidney. SEveral methodological problems inherent in the construction and in vivo application of such microelectrodes were considered, in particular the identification of leaky impalements and the correct assessment of alpha Ki during reversible perfusion of peritubular capillaries from control to a test solution. Peritubular potassium concentration (CpK) could be altered by means of double-barreled micropipettes containing a physiologic and a high or low K solution. The control alpha Ki value averaged 57.9 +/- 8.5 mM (mean +/- SD, n = 38) and the basolateral membrane potential was -70.4 +/- 5.8 mV. Thus, the K+ equilibrium potential across the basolateral membrane (EK) was -81.1 +/- 3.4 mV. Increasing CpK from 3.0 to 30.0 mM raised alpha Ki by 7.0 +/- 1.5 mM, and lowering CpK to 0.3 mM decreased alpha Ki by 9.2 +/- 2.9 mM. CONCLUSIONS: 1) the steady-state K+ distribution across the basolateral membrane indicates that potassium is actively pumped into the cell. 2) The relative stability of alpha Ki in the face of large CpK variations underscores the effectiveness of cell homeostasis; passive mechanisms appear to contribute to this end.

Animals↗
PubMed1982

Glaphenine-induced acute renal failure in the rat: a new experimental model.

Glaphenine, a nonsteroid analgesic compound, administered by gastric gavage in rats (800 mg/kg), induced nonoliguric reversible acute renal failure (ARF). Intratubular deposits were found in medullary collecting ducts. Intratubular hydrostatic pressure (Pt) increased from 11.7 +/- 0.7 to 30.0 +/- 0.9 mmHg. Renal failure was almost completely prevented by concomitant high water and solute diuresis, achieved by furosemide infusion in Wistar rats and by high salt intake in Brattleboro rats with diabetes insipidus. In the latter protected animals, Pt was only slightly elevated (17.0 +/- 0.5 mmHg). Urinary excretion of prostaglandin E2 (PGE2) dropped dramatically after glaphenine administration in Wistar rats; the fall was slight in Brattleboro rats in which PGE2 excretion was normally low. We conclude that tubular obstruction plays a prominent role in glaphenine-induced ARF in the rat. High water and solute diuresis prevented tubular obstruction. Reduced renal PGE2 synthesis is probably not involved in the pathophysiology of this ARF model, inasmuch as Brattleboro rats on a high salt intake were protected despite low basal urinary excretion of PGE2.

Acute Kidney Injury↗
PubMed1982

Effects of ouabain on the electrophysiological properties of proximal tubular cells.

The properties of the Na-K pump were studied by electrophysiological techniques in the proximal tubule of Necturus kidney. Peritubular capillaries were perfused for a short time with different artificial solutions, then ouabain (50 microM-1 mM) was added to each perfusate and its effects on cell membrane potential were assessed. Addition of ouabain, 1 mM, in a physiologic Ringer's solution (K concentration = 3 mM) failed to produce immediate depolarization. The introduction of the cardiac glycoside (50 microM) in solutions in which external K+ concentration was lowered to 0.75 or 0.3 mM resulted in depolarization by 4.1 +/- 0.8 and 9.5 +/- 1.4 mV, respectively. Furthermore, ouabain brought about an increase of membrane input resistance when added in a solution of lowered K+ concentration, but not in the presence of physiologic K+ concentrations. Readmission of K+ into a K-free perfusate flowing through the renal capillaries for more than 15 min resulted in hyperpolarization, 7.2 + 2.0 mV. These and other observations suggest that the Na-K pump operates in electrogenic fashion when external K+ concentration is lowered. Yet, part of the depolarizing response to ouabain under these conditions is mediated via ouabain-elicited changes of cell membrane permeabilities. The stoichiometry of the Na-K pump at physiologic external K concentrations cannot be assessed from the present experiments.

Animals↗
PubMed1981

The effects of barium on the electrical properties of the basolateral membrane in proximal tubule.

We studied the effects of millimolar Ba2+ concentrations on the properties of the basolateral membrane of the proximal tubule in Necturus kidney. Ba2+ was added in the peritubular perfusate by means of capillary microperfusion experiments. Basolateral membrane p.d. and conductance were continuously monitored in single tubules (their lumen was filled with oil) during reversible application of Ba2+ in peritubular fluid. The effect was membrane depolarization by 14mV and a decrease of membrane conductance to 63% of control values. This association strongly suggests that the main effect of Ba2+ is a decrease of the partial conductance to K+ at the basolateral membrane. However, in other experiments, performed also in oil-filled tubules, Ba2+ was shown to decrease intracellular K+ activity, recorded continuously by means of double-barreled (selective vs non selective) K+ microelectrodes. This and other, indirect evidence support the hypothesis that Ba2+ elicits also a small increase of the partial conductance to sodium at the basolateral membrane.

Animals↗
PubMed1981

Chloride distribution in the proximal convoluted tubule of Necturus kidney.

To assess the mechanism(s) by which intraluminal chloride concentration is raised above equilibrium values, intracellular Cl- activity (alpha iCl) was studied in the proximal tubule of Necturus kidney. Paired measurements of cell membrane PD (VBL) and Cl-selective electrode PD (VBLCl) were performed in single tubules, during reversible shifts of peritubular or luminal fluid composition. Steady-state alpha iCl was estimated at 14.6 +/- 0.6 mmol/liter, a figure substantially higher than that predicted for passive distribution. To determine the site of the uphill Cl- transport into the cell, an inhibitor of anion transport (SITS) was added to the perfusion fluid. Introduction of SITS in peritubular perfusate decreased alpha iCl, whereas addition of the drug in luminal fluid slightly increased alpha iCl; both results are consistent with basolateral membrane uphill Cl- transport from interstitium to the cell. TMA+ for Na+ substitutions in either luminal or peritubular perfusate had no effect on alpha iCl. Removal of bicarbonate from peritubular fluid, at constant pH (a situation increasing HCO3- outflux), resulted in an increase of alpha iCl, presumably related to enhanced Cl- cell influx: we infer that Cl- is exchanged against HCO3- at the basolateral membrane. The following mechanism is suggested to account for the rise in luminal Cl- concentration above equilibrium values: intracellular CO2 hydration gives rise to cell HCO3- concentrations above equilibrium. The passive exit of HCO3- at the basolateral membrane energizes an uphill entry of Cl- into the cell. The resulting increase of alpha iCl, above equilibrium, generates downhill Cl- diffusion from cell to lumen. As a result, luminal Cl- concentration also increases.

Animals↗
PubMed1980

Conductive properties of the proximal tubule in Necturus kidney.

The electrical properties of the proximal tubule of the in vivo Necturus kidney were investigated by injecting current (as rectangular waves) into the lumen or into the epithelium of single tubules and by studying the resulting changes of transepithelial (VL) and/or cell membrane potential (VC) at various distances from the source. In some experiments paired measurements of VL and VC were performed at two abscissas x and x'. The luminal length constant of about 1,030 micrometer was shown to provide a good estimate of the transepithelial resistance, specific resistance (RTE = 420 omega.cm2) and/or per unit length (rTE = 1.3 x 10(4) omega.cm). The apparent intraepithelial length constant was subject to distortions arising from concomitant current spread in the lumen. The resistances of luminal membrane (rL), basolateral membrane (rB), and shunt pathway (rS) were estimated by two independent methods at 3.5 x 10(4), 1.2 x 10(4), and 1.7 x 10(4) omega.cm, respectively. The corresponding specific resistances were close to 1,200, 600, and 600 omega.cm2. There are two main conclusions of this study. (a) The resistances of cell membranes and shunt pathway are of the same order of magnitude. The figure of the shunt resistance is at variance with the notion that the proximal tubule of Necturus is a leaky epithelium. (b) A rigorous assessment of the conductive properties of concentric cylindrical double cables (such as renal tubules) requires that electrical interactions arising from one cable to another be taken into account. Appropriate equations were developed to deal with this problem.

Animals↗
PubMed1980

Cytoplasmic regulation of tight-junction permeability: effect of plant cytokinins.

The significance of the "leaky" tight junction might be understood better if cells of the epithelial monolayer possessed mechanisms to regulate molecular flow through the junction. To test this possibility, Necturus gallbladder, a representative leaky epithelium, was studied before, during, and after mucosal exposure to plant cytokinins and two other microfilament-active drugs, cytochalasin B and phalloidin. Concomitant with morphological changes in microfilaments, cytokinins induced rapid reversible increases in transepithelial resistance and potential difference (PD) and decreases in NaCl dilution potentials, with no change in the ratio of relative cell membrane resistances. Cytochalasin B (0.2-1.2 microM) and phalloidin (0.6-12.7 microM) caused similar changes in transepithelial resistance and PD. When the intramembranous structure of tight junctions was studied by freeze fracture, peak cytokinin-induced increments in transepithelial resistance were associated with more disorder in the strand meshwork resulting in a small increase in tight junction depth, but there was no evidence of de novo strand assembly. These studies suggest that permeability of the tight junction of Necturus gallbladder is subject to rapid reversible modulation, possibly under cytoskeletal control.

Animals↗
PubMed1978

The effect of a disulfonic acid stilbene on proximal cell membrane potential in Necturus kidney.

The effects of 0.5 mM 4-acetamido-4'-isothiocyano-stilbene-2,2' disulfonic acid on the electrical properties of the peritubular membrane were studied in the proximal tubule of the perfused Necturus kidney. The addition of stilbene isothiocyanate disulfonic acid in peritubular perfusate resulted in an average 4.5 mV hyperpolarization with no detectable changes of peritubular membrane input conductance. The depolarization elicited by high-K media was enhanced by 18% in the presence of stilbene isothiocyanate disulfonic acid, an observation indicating that the inhibitor increased the contribution of potassium to membrane potential, presumably by decreasing anionic permeabilities. The hyperpolarizing effect of stilbene isothiocyanate disulfonic acid was abolished when peritubular bicarbonate was removed from the medium and isoosmotically replaced by chloride. These data suggest that (a) intracellular bicarbonate activity is higher than that predicted from passive distribution, (b) stilbene isothiocyanate disulfonic acid decreases P HCO3, thus hyperpolarizing the membrane, (c) chloride distribution appears to be passive when bicarbonate is removed from the peritubular perfusate. The state of Cl distribution when extracellular bicarbonate is at physiologic concentration cannot be assessed from the present data.

Animals↗
PubMed1978

[Effects of salicylate on the electrical properties of the proximal convoluted tubule of Necturus maculosus].

The effects of peritubular salicylate for chloride substitution were studied in the isolated perfused Necturus kidney. This substitution resulted in changes of cell membrane p.d., varying from tubule to tubule; the withdrawal of the test-anion invariably produced a steep and prolonged depolarization. Exposure of the tissue to salicylate brought about, in addition, electrical uncoupling of junctional membranes, which was not related to concomitant changes of membrane p.d.

Animals↗
PubMed1978

Further studies on ion permeation in proximal tubule of necturus kidney.

In the perfused Necturus kidney, the ratio of transepithelial sodium-to-chloride permeabilities (PNa/PCl) was estimated from dilution potentials at 1:7. The ratio of transepithelial permeabilities PHCO3/cl was estimated from bi-ionic potentials at 1:4 and that of Plact/PCl at 1:12. The permeability sequence, therefore, is PCl greater than PHCO3 greater than than PNa or PnaCl greater than PNaHCO3. The latter is similar to the situation in the rat. However, because of the low Na permeability, passive NaCl absorption by solvent drag is probably less important in Necturus than in the rat. The measurement of transepithelial input conductance during replacement of extracellular chloride by either bicarbonate or lactate shows that the former reduces the transmural conductance to 31% of control values as compared with 40% for the latter. Such discrepancies between permeability and conductance sequences are consistent either with an interference of the test anion with chloride permeation or with the presence of positive fixed changes within the shunt pathway.

Animals↗
PubMed1977

Electrophysiological study of the antiluminal membrane in the proximal tubule of Necturus: effect of inorganic anions and SCN-.

1. A study has been made of the effects of anionic substitutions on the electrical potential difference (p.d.) and conductance characteristics of the antiluminal (peritubular) membrane of the proximal tubule of Necturus kidney. The tubular lumina were filled with oil in order to minimize potential and conductance contributions from luminal membrane and from paracellular shunt pathway.2. Isosmotic substitutions, [A](o) for [Cl](o), produced the following average changes in membrane p.d. (mV): F(-) +1.7, BrO(3) (-) +0.1, Br(-) -4.5, ClO(3) (-) -5.2, I(-) -7.9, NO(3) (-) -12.1, ClO(4) (-) -17.8, SCN(-) -25.3.3. The amplitude of the depolarization caused by increase in K concentration (K-depolarization) in the peritubular perfusate was found to increase during perfusion of the tissue with ClO(4) (-) (by 78%), SCN(-) (45%), I(-) (23%), NO(3) (-) (20%), Br(-) (16%); it decreased with F(-) (by 17%).4. Comparison of membrane p.d. at peak K-depolarization in the control state (during KCl perfusion) with that obtained in the experimental state (during KA perfusion) was found to be more reliable than determination of bi-ionic potentials as a qualitative estimate of the permeabilities of the various anions (P(A)) relative to that of chloride (P(Cl)).5. Study of both peak K-depolarization p.d. and bi-ionic potentials yielded the following sequence for halide anion permeabilities: P(F) > P(Cl) > P(Br) > P(I). The peritubular membrane was found to be substantially more permeable to NO(3) (-), ClO(4) (-) and SCN(-) than to Cl(-).6. The sequence of membrane conductances during anionic substitutions was Cl(-) approximately BrO(3) (-) < Br(-) </= ClO(3) (-) < I(-) approximately F(-) < NO(3) (-) < ClO(4) (-) < SCN(-).7. From the changes in p.d. induced by K-depolarization, the absolute values of p.d. at peak K-depolarization and from the changes in membrane conductance induced by anionic substitutions, it may be inferred that Br(-), I(-), NO(3) (-), ClO(4) (-) and SCN(-) all increase P(K); and that F(-) increases P(Na) (though a smaller increase in P(K) cannot be excluded).

Animals↗
PubMed1976

Transepithelial potential difference in the proximal tubule of necturus kidney.

Transepithelial potential difference (p.d.) was measured in the proximal tubule of Necturus kidney in vivo, by means of microelectrodes filled either with a 3M KClion or with a Ringer's solution for amphibians. The average transepithelial p.d., measured with KCl-tips, was: -1.4 +/- 2.4 mV (early convolutions), -0.1 +/- 2.0 mV (middle convolutions) and +0.1 +/- 2.4 mV (straight segment). The corresponding values obtained with Ringer's-filled microelectrodes were -2.3 +/- 1.8 mV, -1.3 +/- 1.1 mV and +0.1 +/- 1.2 mV, respectively. Tip localization into the lumen was ascertained by luminal injection of either oil (KCl electrode measurements) or artificial solutions which produced a measurable shift of transepithelial p.d. (determinations obtained with Ringer's-tips). Transepithelial p.d. in split-drops (mean reabsorptive half time 27.1 +/- 2.5 min) was -1.8 +/- 1.1 mV. The magnitude of transepithelial p.d. is discussed with respect to an equivalent electrical circuit; it is shown that high transepithelial p.d.'s are inconsistent with the known values of relative conductances of cell membranes in series and shunt pathway, respectively.

Animals↗
PubMed1975

Anion permeation in the proximal tubule of Necturus kidney: the shunt pathway.

The effect of foreign anions on transepithelial potential difference and transepithelial input conductance was studied in the isolated perfused Necturus kidney. Two microelectrodes (recording and current-injecting) were inserted into the lumen of single proximal tubules and the peritubular perfusate was shifted reversibly for 30-60 sec from a physiologic Ringer's solution to a test solution in which chloride was replaced isosmotically by a foreign anion. The permeability sequence, obtained by potential measurements, was: lactate less than glutamate less than gluconate less than pyruvate less than benzene sulfonate less than or equal to acetate less than or equal to F less than propionate less than BrO3 less than formate less than ClO3 less than Cl than ClO4 less than I less than or equal to Br less than NO3 less than SCN. Transepithelial conductance decreased when the tissue was perfused with anions less permeable than chloride but the conductance sequence was different from the permeability sequence. Such discrepancies were more pronounced during perfusion with hyperpolarizing anions; ClO4 and I- (both more permeable than chloride) produced an important decrease in transepithelial conductance, followed by incomplete reversibility when the perfusion was shifted again to chloride Ringer's. The results are best explained by the presence of weak positive fixed charges, governing anion permeation, at the shunt pathway of the proximal tubule. An analysis of the data allows tentative estimates of shape and size of the sites.

Animals↗