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M Wiederholt

Publications and source records attributed to M Wiederholt.

At least 109 records · Page 6Linked to original sources
PubMed1986

Interactions of pH and K+ conductance in cultured bovine retinal pigment epithelial cells.

Passive ion transport properties were studied in confluent monolayers of cultured bovine retinal pigment epithelial cells using intracellular microelectrode technique. The mean stable intracellular (designated by subscript i) potential was -59.1 +/- 0.8 (SE) mV. Extracellular (designated by subscript o) acidification induced a depolarization, whereas alkalinization induced a hyperpolarization. These effects were observed both in bicarbonate-free as well as in HCO3- Ringer (pHo changed by varying [HCO3-]o at constant pCO2). Acidification of pHi (changed by addition and removal of butyrate, CO2 or NH3) also caused a depolarization. Complete removal of HCO3-/CO2 at constant pHo caused a hyperpolarization. K+ transference, checked by applying high K+o, increased with K+o. It decreased with both extra and intracellular acidification and increased with alkalinization. In the presence of Ba2+, voltage reactions to changes in either pHo or pHi were greatly reduced. Depolarization by 40 mM K+ caused a similar reduction. It is suggested that K+ conductance of bovine retinal pigment epithelial cells is reduced by either intra- or extracellular acidification at normal [K+]o. Depolarization by high K+ induces an increase in K+ transference and reduces pH sensitivity.

Action Potentials↗
PubMed1986

Electrical properties of sodium bicarbonate symport in kidney epithelial cells (BSC-1).

Intracellular potentials of BSC-1 kidney epithelial cells known to express a Na+-HCO3- symport ranged between -40 and -70 mV, mean value Vm = -55.1 +/- 10.1 mV. Lowering HCO3- at constant partial pressure of CO2 (PCO2) or complete removal of HCO3-/CO2, rapidly depolarized, whereas readding HCO3- hyperpolarized Vm (40 +/- 8 mV/decade HCO3- at constant PCO2). This response was largely reduced by 1 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) (which depolarized Vm to about -20 mV) and in Na+-free medium, but Ba2+ had no effect. In HCO3(-)-Ringer, Na+ removal rapidly depolarized Vm (by 32 +/- 7 mV), and readdition hyperpolarized Vm. This was reduced in HCO3(-)-free medium or by 1 mM DIDS, but not by amiloride (10(-5) and 10(-3) M) or ouabain (10(-4) M). In the absence of HCO3- and/or Na+, steady-state Vm was reduced to -12 +/- 5 mV. Cl- removal had no effect on the responses to Na+ and/or HCO3- and led to a slow steady-state depolarization. Both in the presence and absence of HCO3-, raising pHi (changed by NH4Cl or butyrate) depolarized, whereas lowering pHi hyperpolarized Vm. Lowering pHo in HCO3(-)-free Ringer depolarized Vm (23 +/- 4 mV/decade H+). The slope conductance for K+ is only 6 +/- 2 mV/decade. Thus BSC-1 cells display typical electrical characteristics of Na+-HCO3- symport. In contrast to other systems, the data are compatible with a net electrogenic inward transport of Na+ and HCO3-. There might be an additional H+-(OH-) conductance operating also under nominally bicarbonate-free conditions.

Amiloride↗
PubMed1986

Pharmacokinetic of topical cyclosporin A in the rabbit eye.

3H labelled cyclosporin A (CS-A) eye drops (2% in castor oil) were applied in rabbits. When a single drop of 10 microliters was given CS-A reached a maximal concentration of 900-1400 ng/ml in the cornea 6 hr after application and then slowly decreased. A substantial level of 600-900 ng/ml was still present after 48 hr. When corneas were analysed for their cellular compartments, 67% of CS-A was found in the epithelium, 25% in the stroma (probably in keratocytes), and 8% in the endothelium. In corneas denervated by circular keratotomy, slightly reduced concentrations were found after surgery, the reduction was not therapeutically significant. Using the HPLC method a significant corneal metabolism of CS-A could be excluded. Scleral concentrations of CS-A as high as 180 ng/ml were found. Concentrations of CS-A in aqueous humor, lens, vitreous body and uvea/retina were below the therapeutic range.

Animals↗
PubMed1985

Kidney epithelial cells of monkey origin (BSC-1) express a sodium bicarbonate cotransport. Characterization by 22Na+ flux measurements.

Na movement across the plasma membranes of confluent monolayers of monkey kidney epithelial cells (BSC-1) was studied using 22Na+ uptake and efflux techniques in the presence of 10(-4) M ouabain. In the presence of 28 mM bicarbonate, uptake was inhibited by both 10(-3) M amiloride and 10(-3) M 4,4'diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). In DIDS-pretreated cells, 10(-3) M amiloride led to a further reduction of 22Na+ uptake, while 10(-5) furosemide was ineffective. DIDS also inhibited sodium efflux, indicating that the DIDS-sensitive pathway mediates both influx and efflux of 22Na+. DIDS-sensitive 22Na+ uptake, as studied in the presence of both 10(-4) M ouabain and 10(-3) M amiloride, was abolished by the absence of bicarbonate, which could not be substituted by other plasma membrane-permeable buffers. In 28 mM HCO3-, DIDS-sensitive uptake of 28 mM Na+ was cis-inhibited by 124 mM Na+, but no significant inhibition by K+ or Li+ was found. DIDS-sensitive 22Na+ uptake was a saturable function of both Na+ concentration (apparent Km between 20 and 40 mM at 28 mM HCO3-) and HCO3- concentration (apparent Km between 7 and 14 mM at 151 mM Na+). Intracellular microelectrode measurements showed that net Na+ transport in the presence of HCO3- is electrogenic, i.e. that there is anion cotransport with Na+. This effect is abolished by 1 mM DIDS. It is concluded that monkey kidney epithelial cells possess a stilbene-sensitive, electrogenic sodium bicarbonate symport, which may play an important role in bicarbonate reabsorption in the mammalian kidney.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1985

A bicarbonate-dependent process inhibitable by disulfonic stilbenes and a Na+/H+ exchange mediate 22Na+ uptake into cultured bovine corneal endothelium.

22Na+ uptake into confluent monolayers of cultured bovine corneal endothelial cells was studied in the presence of ouabain (10(-4)M) to inhibit active sodium extrusion. In bicarbonate saline, uptake was reduced to a similar degree either by amiloride (10(-3)M) or by 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) (10(-3)M). A further reduction was obtained with SITS-pretreated cells in the presence of amiloride. SITS-sensitive uptake was further characterized in saline containing both ouabain (10(-4)M) and amiloride (10(-3)M). It was absolutely dependent on bicarbonate, which could not be substituted by other plasma membrane permeable buffers (50 mM acetate or 25 mM glycodiazine). It was a saturable function of both bicarbonate and sodium concentration. Half-maximal fluxes occurred between 3 and 7 mM HCO3 (at 151 mM Na) and between 35 and 60 mM Na (at 28 mM HCO3). Uptake into sodium-depleted cells was reduced as opposed to sodium-rich cells, and SITS-sensitive 22Na+ efflux out of 22Na+-loaded cells into sodium-free medium was less than efflux into sodium saline, indicating trans-stimulation by sodium. The amiloride-sensitive pathway was studied in the absence of bicarbonate to inhibit uptake via the SITS-sensitive pathway. 22Na+ uptake into sodium-depleted cells increased steeply with extracellular pH in the range between pH 6 and 8 and could be largely blocked by 10(-3), but not by 10(-5) M amiloride. It is concluded that bovine corneal endothelial cells possess at least two distinct pathways for sodium uptake, amiloride sensitive 22Na+ fluxes being mediated by a Na+/H+ antiport, while the SITS-sensitive process is probably identical to a bicarbonate-sodium cotransport system postulated earlier from electrophysiological studies.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1985

Electrogenic sodium-bicarbonate symport in cultured corneal endothelial cells.

Intracellular potential measurements on confluent monolayers of cultured bovine corneal endothelial cells were used to define passive ion transport processes in these cells. Previous studies [11, 12] have provided the experimental basis for a cellular model, is which bicarbonate entry across the basolateral membrane in indirectly driven by a Na+/H+-exchanger, which is inhibitable by amiloride (1 mmol/l). Na+ and HCO3- leave the cell via an electrogenic bicarbonate sodium cotransport, which is inhibitable by the disulfonic stilbene derivates SITS or DIDS. This model is also compatible with transepithelial work from other groups. In this paper, we briefly review the evidence we have obtained for this model.

Amiloride↗
PubMed1985

Anion dependence of electrical effects of bicarbonate and sodium on cultured bovine corneal endothelial cells.

Using intracellular microelectrode technique, the effect of anion substitution on the voltage responses to extracellular bicarbonate and sodium was explored in cultured bovine corneal endothelial cells. The overall amplitude of voltage changes induced by periodic changes of [HCO-3]o (depolarization upon removal of HCO-3 and hyperpolarization upon readdition) was reduced when Cl- was replaced by organic anions (cyclamate, methylsulfate, benzenesulfonate) or by SO4(2-), and to a lesser extent by substitution with Br-. There was a similar effect of anion substitution on the response to changes of [Na+]o. In both cases, in the absence of Cl, the voltage V returned at a slower rate to baseline levels after it had been transiently changed by either an imposed Na- or HCO3- gradient, indicating a slower dissipation of these gradients. The direct response of V to these imposed gradients was affected only to a minor degree. Replacement of Cl- by SO4(2-) or organic anions led to a slow, reversible depolarization of the cell, while substitution with Br- had only a slight effect. The effect of anion substitution on the voltage responses to HCO-3 or Na+ could not be mimicked by a depolarization induced by Ba2+ (1 mM). Furosemide (10(-3) M) led to a slight reduction of the voltage responses to HCO-3, but could not suppress the effect of anion substitution on these reactions. It could neither suppress the depolarization induced by anion substitution and had no effect on steady-state PD. It is suggested, that cultured bovine corneal endothelial cells, in addition to a previously demonstrated electrogenic HCO-3-Na+-cotransport, which is probably not dependent on Cl, possess an electroneutral mechanism for HCO-3 and/or Na+-movement, which depends on Cl. No evidence for a Cl-conductance could be obtained.

Animals↗
PubMed1985

Response of the intracellular potentials of cultured bovine lens cells to ions and inhibitors.

Micropuncture of bovine lens epithelial cells cultured on plastic culture dishes gave values for the plasma membrane voltage (V) which remained stable for periods of up to several hours. The value of V was mainly in the range -30 to -45 mV, mean value -36.9 +/- 0.5 mV (S.E.M., n = 188). Raising extracellular [K+] from 5 to 40 mM depolarized V by 10 +/- 3 mV. The extent of this depolarization increased with increasing steady-state V. Barium (2 mM) caused a rapid, reversible depolarization of 7.9 +/- 1.2 mV. In the presence of Ba2+, the response to 40 mM K was reduced to 3.6 +/- 1.1 mV. Ouabain (10(-5) M) caused a fast depolarization by 5.3 +/- 1.2 mV. Exposure to calcium-free EGTA-Ringer's depolarized V reversibly by 19.5 +/- 5.0 mV. In Ca-free medium, the depolarization induced by 40 mM K was reduced to 3.2 +/- 2.4 mV. Whereas in control Ringer's sodium conductance (as measured by exposure to a 10 mM [Na]-Ringer's) is small as compared to potassium conductance, it increased markedly in Ca-depleted medium. Amiloride (10(-4) and 10(-3) M) had no effect on this Na conductance. An increase in the relative conductance for sodium was also elicited by Ba2+ (2 mM). Extracellular acidification led to a depolarization, alkalinization to a hyperpolarization. The extent of this effect was virtually equal in the absence or presence of HCO3-, excluding a significant pathway for bicarbonate. No evidence for a significant chloride conductance could be obtained.

Amiloride↗
PubMed1985

[Local treatment of corneal transplants in the human with cyclosporin A].

Cyclosporin eye drops (2% in miglyol) were administered in 4 glaucoma patients for postoperative treatment following keratoplasty. In the course of the 2-year follow-up period, one patient evidenced an immunoreaction that led to clouding of the transplant. In 25 patients, Cyclosporin eye drops (2% in castor oil) were given in combination with low-dose dexamethasone eye drops (0.1%). During a mean follow-up period of 10 months (5 to 14 months), 4 transplants clouded as the result of an immunoreaction. The intraocular pressure was not influenced by the combination therapy in 21 patients who did not have a history of glaucoma but increased slightly in 3 of 4 patients who did. Since Cyclosporin A had no influence on the stromal wound healing, it was possible to remove the corneal sutures 5 months postoperatively. All patients developed keratopathia punctata and slight conjunctivitis. The epithelial defects, which often showed a vortex-like pattern, appeared at the end of the first postoperative week and were usually no longer detectable after 4 months. The tear production (Schirmer test) was not influenced or only slightly increased by Cyclosporin. Corneal infiltrates did not occur. If one compares the effects and side effects of Cyclosporin and dexamethasone, local application of Cyclosporin in combination with low-dose dexamethasone appears to be an effective treatment for corneal transplantation in Man.

Adult↗
PubMed1985

A randomised prospective study on treatment of central retinal vein occlusion by isovolaemic haemodilution and photocoagulation.

Thirty eight patients with ischaemic and non-ischaemic central retinal vein occlusion were evaluated for the effect of isovolaemic haemodilution. They were allocated at random to a haemodilution group (19 patients, panretinal photocoagulation and isovolaemic haemodilution) and a control group (19 patients, panretinal photocoagulation). Haematocrit was lowered in steps to 30 to 35% in the haemodilution group by repeated exchanges of whole blood for plasma and dextran (MW 40 000) and kept at this level for a period of six weeks. The haemodilution did not lead to serious complications. Three months after starting the treatment eight of 19 patients with haemodilution showed a better visual acuity, whereas only one of 19 control patients had improved. Seven of 17 patients with haemodilution, but only one of 17 control patients, retained a better visual acuity after one year. In the haemodilution group there were fewer patients with macular fibrosis and more with only minor foveal changes. The haemodilution seems to be more effective in patients with ischaemic than with non-ischaemic central retinal vein occlusion. It is concluded that isovolaemic haemodilution improves the visual outcome of patients with central retinal vein occlusion, probably mediated by enhanced retinal blood flow.

Aged↗
PubMed1985

Ion transport mechanisms in cultured bovine corneal endothelial cells.

Intracellular potential measurements of confluent monolayers of cultured bovine corneal endothelial cells were used to define passive ion transport processes in these cells. Previous studies (Jentsch et al., J. Membr. Biol. 78:103 (1984); Jentsch et al., J. Membr. Biol. 81:189 (1984] have provided the experimental basis for a cellular model, in which bicarbonate entry across the basolateral membrane is indirectly driven by a Na+/H+-exchanger, which is inhibitable by amiloride (1mM). Bicarbonate and sodium should leave the cell via an electrogenic bicarbonate sodium cotransport, which is inhibitable by the disulfonic stilbene derivates SITS or DIDS. This model is also consistent with results from transendothelial studies. In this paper, we briefly review the evidence we have obtained for this model and demonstrate, that the electrical response to sodium (depolarization upon Na+-removal) is neither due to an inhibition of Na+/K+-ATPase nor explainable in terms of changes in K+-conductance. This is concluded from the observation of these responses in the presence of ouabain (10(-4)M) or barium (1mM).

Animals↗
PubMed1985

Effect of corticosteroids on electrolyte transport of the isolated human and rabbit lens.

In the isolated human lens, short circuit current was inhibited by pharmacological concentrations of 6-methylprednisolone and opacities occurred in the posterior subcapsular region in some lenses. The effect was seen only when the anterior (epithelial) surface of the lens was exposed. There was an increase of the short circuit current in the rabbit lens by 6-methyl-prednisolone and the lenses remained clear. Methylprednisolone effects were seen in spite of Na-K-ATPase inhibition by ouabain. Aldosterone had no effect on the translenticular potential difference, short circuit current and transparency. The data are discussed with respect to corticosteroid receptors in the lens epithelium and to the pathogenesis of steroid-associated cataract in man.

Aldosterone↗
PubMed1984

Aldosterone secretion, measurements of membrane potential and intracellular potassium activity in the isolated adrenal zone glomerulosa.

Cell membrane potential and intracellular potassium activity (microelectrodes filled with ion-sensitive liquid ion exchanger) were measured in the zona glomerulosa of superfused hemi-adrenals of rats kept on different diets. Simultaneously, samples of the superfusate were collected and analyzed by radioimmunoassay for aldosterone content. Cell membrane potential and intracellular potassium activity were not influenced by high sodium, low sodium or high potassium diet. However, aldosterone secretion significantly changed. These results suggest that membrane potential and intracellular potassium activity per se may not be linked to changes in aldosterone secretion.

Adrenal Glands↗
PubMed1984

Evidence for coupled transport of bicarbonate and sodium in cultured bovine corneal endothelial cells.

Using intracellular microelectrode technique, the response of the voltage V across the plasma membrane of cultured bovine corneal endothelial cells to changes in sodium and bicarbonate concentrations was investigated. (1) The electrical response to changes in [HCO3-]o (depolarization upon lowering and hyperpolarization upon raising [HCO3-]o) was dependent on sodium. Lithium could fairly well be substituted for sodium, whereas potassium or choline were much less effective. (2) Removal of external sodium caused a depolarization, while a readdition led to a hyperpolarization, which increased with time of preincubation in the sodium-depleted medium. (3) The response to changes in [Na+]o was dependent on bicarbonate. In a nominally bicarbonate-free medium, its amplitude was decreased or even reversed in sign. (4) Application of SITS or DIDS (10(-3) M) had a similar effect on the response to sodium as bicarbonate-depleted medium. (5) At [Na+]o = 151 mM and [HCO3-]o = 46 mM, the transients of V depended, with 39.0 +/- 9.0 (SD) mV/decade, on bicarbonate and, with 15.3 +/- 5.8 (SD) mV/decade, on sodium. (6) After the preincubation of cells with lithium, replacement of Li by choline led to similar effects as the replacement of sodium by choline, though the response of V was smaller with Li. This response could be reduced or reversed by the removal of bicarbonate or by the application of SITS. (7) Amiloride (10(-3) M) caused a reversible hyperpolarization of the steady-state potential by 8.5 +/- 2.6 mV (SD). It did not affect the immediate response to changes in [Na+]o or [HCO3-]o, but reduced the speed of regaining the steady-state potential after a change in [HCO3-]o. (8) Ouabain (10(-4) M) caused a fast depolarization of -6.8 +/- 1.1 (SD) mV, which was followed by a continuing slower depolarization. The effect was almost identical at 10(-5) M. (9) It is suggested, that corneal endothelial cells possess a cotransport for sodium and bicarbonate, which transports net negative charge with these ions. It is inhibitable by stilbenes, but not directly affected by amiloride or ouabain. Lithium is a good substitute for sodium with respect to bicarbonate transport and is transported itself. In addition, the effect of amiloride provides indirect evidence for the existence of a Na+/H+-antiport. A model for the transepithelial transport of bicarbonate across the corneal endothelium is proposed.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗