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Biomedical subjects

M Wiederholt

Publications and source records attributed to M Wiederholt.

At least 55 records · Page 3Linked to original sources
PubMed1992

Haemorheological parameters in patients with retinal artery occlusion and anterior ischaemic optic neuropathy.

The haemorheological parameters haematocrit (Hct), plasma viscosity (PV), red cell aggregation (RCA), red cell filterability (RCF), apparent whole blood viscosity (WBV), and fibrinogen were measured in 31 patients with retinal artery occlusion (RAO), 25 patients with anterior ischaemic optic neuropathy (AION), and 19 patients with giant cell arteritis (GCA). The patient groups were compared with controls of same age and similar prevalence of cardiovascular risk factors. Patients with RAO and AION have a significantly decreased RCF in comparison with controls. All other parameters showed no differences. Patients with GCA had significantly decreased Hct and RCF and increased PV and fibrinogen. After 2 weeks of systemic treatment with high dose steroids in patients with GCA the plasma viscosity had returned to normal and was even lower than in controls, and the Hct and fibrinogen had reached normal levels.

Adult↗
PubMed1992

Electrogenic sodium-bicarbonate cotransport in human ciliary muscle cells.

We investigated membrane voltage and intracellular pH (pHi) in cultured human ciliary muscle cells using a cell line (H7CM) and primary-cultured human ciliary muscle cells. 1) Resting potential was 58.9 +/- 1.0 mV in H7CM cells and 61.9 +/- 1.4 mV in primary cultures. The following data are from H7CM cells, but results from primary cultures were basically similar. 2) In HCO3(-)-CO2-buffered solution, removal of extracellular sodium resulted in a depolarization [change in membrane resistance (delta V) = 31.3 +/- 2.8 mV] that was less marked in the absence of HCO3(-)-CO2 (delta V = 0.5 +/- 2.6 mV) and reduced by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) (delta V = 19.3 +/- 1.9 mV). 3) Removal of extracellular HCO3(-)-CO2 led to a depolarization (delta V = 13.2 +/- 0.8 mV) that was abolished in the absence of extracellular sodium and inhibited by DIDS. 4) Intracellular alkalinization led to a depolarization (delta V = 24.7 +/- 2.3 mV), and intracellular acidification resulted in a hyperpolarization (delta V = 9.4 +/- 1.1 mV) that was inhibited by DIDS and dependent on extracellular HCO3(-)-CO2 and sodium. 5) pHi backregulation after an acid load occurred in both the presence and absence of extracellular bicarbonate but not in the absence of extracellular sodium. Our data are consistent with an electrogenic Na(+)-HCO3- cotransport in human ciliary muscle cells, which is activated by intracellular acidification.

Bicarbonates↗
PubMed1992

Endothelin-like immunoreactivity in the aqueous humour and in conditioned medium from cultured ciliary epithelial cells.

Endothelin-like immunoreactivity was detected in human (15.6 +/- 2.7 pg/ml) and bovine (11.1 +/- 0.98 pg/ml) aqueous humour of the eye. These concentrations are 2-3 times higher than the corresponding plasma levels. Cultured human nonpigmented ciliary epithelial cells released endothelin-like immunoreactivity with a maximum of 2.1 +/- 0.32 pg/(cm2* 48 h). The release was stimulated by fetal calf serum, thrombin, carbachol and phorbol ester and blocked by cycloheximide. Immunocytochemistry showed cytoplasmic staining of cultured human nonpigmented ciliary epithelial cells for endothelin-1. Endothelin-1 was shown to induce contractions in isolated human ciliary muscle by isometric force measurements. Endothelin in the aqueous humour may play a role in the regulation of intraocular pressure.

Animals↗
PubMed1992

Membrane potentials in retinal capillary pericytes: excitability and effect of vasoactive substances.

Retinal capillary pericytes are believed to have a contractile function and to regulate retinal blood flow at the microvascular level. Membrane potential is an important control element for contractility in smooth muscle cells. In the present study, bovine retinal capillary pericytes have been grown in tissue culture and membrane potentials have been measured using glass microelectrodes. Resting potentials averaged -31 +/- 7 mV (n = 203). Relative K+ conductance was low, with a transference number for K+ of 0.16. Readdition of K+ to K(+)-depleted cells transiently hyperpolarized the membrane potential, probably by stimulating the electrogenic Na+/K+ transport. Repetitive spike-like depolarizations (action potentials) were induced by stimulating the Na+/K(+)-ATPase, by applying norepinephrine (10(-5) mol/l), and by adding 10 mmol/l Ba2+. These action potentials depended on the presence of extracellular Ca2+ and were inhibited by the Ca2+ antagonist nifedipine (10(-6) mol/l). Norepinephrine (10(-5) mol/l) depolarized the membrane by 7.4 +/- 3.5 mV (mean +/- SD, n = 49). This response was blocked by the alpha 1-antagonist prazosin (10(-5) mol/l). Histamine also led to a membrane depolarization of 8.6 +/- 2.8 mV (n = 49), which could be inhibited by the H1-antagonist diphenhydramine. Endothelin (10(-7) mol/l), vasopressin (10(-6) mol/l), and acetylcholine (10(-4) mol/l) had no major effects on membrane potential. The conclusion is that retinal capillary pericytes are excitable cells and react to several vasoactive substances.

Acetylcholine↗
PubMed1992

Effect of histamine on the membrane potential of cultured human nonpigmented ciliary epithelial cells.

The effect of histamine on the membrane potential of cultured human nonpigmented ciliary epithelial cells was examined using intracellular microelectrodes. The resting voltage was Vm = 42 +/- 0.7 mV (n = 41). Histamine (10(-6) mol/l) induced transient hyperpolarization (V = 19.4 +/- 1.2 mV, n = 35) and subsequent depolarization when applied for more than 1 min. The histamine effect was completely inhibited by the H1 antagonist diphenhydramine (10(-6) mol/l), but not influenced by the H2 antagonist cimetidine (up to 10(-3) mol/l). When histamine was applied repeatedly in the absence of external calcium, the amplitude of the hyperpolarization decreased until finally no response was observed. Ba2+ (2 mmol/l) and quinidine (1 mmol/l), both inhibitors of potassium conductance, significantly reduced histamine-induced hyperpolarization. It was also reduced when cells were depolarized by 40 mmol/l extracellular potassium and almost completely abolished in the presence of 80 mmol/l external potassium. We conclude that H1 receptors mediate hyperpolarization by increasing potassium conductance, probably via transient release of intracellularly stored calcium.

Calcium↗
PubMed1992

Effects of endothelin and calcium channel blockers on membrane voltage and intracellular calcium in cultured bovine trabecular meshwork cells.

The membrane voltage was measured in cultured bovine trabecular meshwork cells. External barium (Ba2+; 10 mM) evoked repetitive overshooting action potentials which were reversibly inhibited by 10(-6) M nifedipine but insensitive to tetrodotoxin (10(-5) M). In contrast, no action potentials could be induced in bovine corneal endothelial cells. The vasoactive peptide endothelin (10(-9)-10(-6) M) induced dose-dependent depolarizations. The intracellular calcium concentration measured by the fura-2 method increased after endothelin application. An initial peak was followed by a sustained plateau. The effect of endothelin on the membrane potential and intracellular calcium value is typical for smooth muscle cells showing a contractile response to the peptide. Recent studies have shown the contractility of bovine trabecular meshwork. We conclude that calcium-channel antagonists and endothelin may alter the aqueous humour outflow through the trabecular meshwork.

Animals↗
PubMed1991

Measurements of intracellular calcium and contractility in human ciliary muscle.

Electromechanical and pharmacomechanical coupling was investigated in human ciliary muscle by measuring the intracellular free calcium in single cultured ciliary muscle cells and the contractility in meridional ciliary muscle strips. The basal resting calcium concentration was 75 +/- 8.7 nmol/l, n = 23. Application of acetylcholine (0.1 mmol/l) and carbachol (0.1 mmol/l) resulted in an initial [Ca2+]i peak followed by a recovery phase and a [Ca2+]i plateau. The initial [Ca2+]i peak was still observed in the absence of extracellular calcium and in the presence of verapamil (0.1 mmol/l). During its plateau [Ca2+]i was decreased by withdrawal of extracellular calcium or application of verapamil (0.1 mmol/l). Depolarization induced by a high level of extracellular potassium yielded only a small transient [Ca2+]i peak without a [Ca2+]i plateau. In isolated ciliary muscle strips, muscarinic stimulation (carbachol 0.1 mmol/l) resulted in an initial phasic and a subsequent tonic contraction. Removal of external calcium reduced the phasic contraction to 30.6 +/- 4.4% (n = 8) and completely abolished the tonic one. Verapamil (0.1 mmol/l) had only a slight relaxing effect when applied during the tonic contraction. We conclude that human ciliary muscle contraction is mediated by calcium release from intracellular stores and calcium entry through calcium channels, which are most probably receptor-operated. Depolarization of the muscle cell membrane and calcium entry through voltage-operated calcium channels do not contribute significantly to human ciliary muscle contraction.

Acetylcholine↗
PubMed1991

Electrical and morphological evidence for heterogeneous populations of cultured bovine trabecular meshwork cells.

Although trabecular meshwork cells are presumed to play an important role in determining ocular aqueous outflow resistance, little is known about their membrane transport characteristics. As in vivo access by microelectrodes is difficult, we used cell culture techniques to facilitate membrane voltage recording from cultured bovine trabecular meshwork cells. Phase-contrast microscopy revealed the presence of epithelial-like and spindle-shaped cell types. The mean membrane voltage for epithelial cells was -49.7 +/- 0.8 mV (S.E.M., n = 143) and for spindle cells was -70.9 +/- 1.9 mV (S.E.M., n = 48). These cells possess an electrogenic Na+/K(+)-ATPase and a K+ conductance. K transference numbers (tk) for [K+] from 5 to 80 mM were 0.50 for epithelial cells and 0.71 for spindle cells. The epithelial cells lack the electrogenic Na+/HCO3-symport, thereby enabling their differentiation from corneal endothelial cells and confirming previous reports of differences between these cell types. A proportion of spindle cells demonstrated spontaneous and induced fluctuations of membrane voltage. One millimolar Ba2+ (n = 9) induced an immediate depolarization of membrane voltage, with the onset of 'overshooting' action potentials, which were dependent on extracellular Ca2+ and Na+ but were not blocked by tetrodotoxin, 10(-6) M. Spindle cells showed parallel alignment of intracellular smooth muscle specific alpha-isoactin filaments, whereas epithelial cells showed specks of non-fibrous staining. Electron microscopy revealed that epithelial cells had the characteristics of metabolically active cells, with few intermediate filaments (10-12 nm) and microfilaments (6-7 nm) and short cytoplasmic processes. Spindle cells had long cytoplasmic processes and abundant intermediate- and microfilaments. These data provide further evidence for multiple bovine trabecular cell types. The smooth muscle-like spindle cell may represent the previously proposed contractile element of the angle and its action could conceivably alter ocular outflow resistance.

Actins↗
PubMed1991

Differential smooth muscle-like contractile properties of trabecular meshwork and ciliary muscle.

The contractile properties of bovine trabecular meshwork and ciliary muscle strips were investigated using an electromagnetic force-length transducer for isometric force measurements. Acetylcholine, pilocarpine and aceclidine administration resulted in dose-dependent contractions of trabecular meshwork and ciliary muscle. Absolute forces were approximately 10 times larger in ciliary muscle than in trabecular meshwork. Maximal force evoked by aceclidine (5 x 10(-5) M), when compared to the pilocarpine (5 x 10(-5) M) response, was significantly higher in trabecular meshwork than in ciliary muscle. The results were 172.5 +/- 12.6% (n = 7) and 138.9 +/- 4.0% (n = 8, P less than 0.05), respectively. Depolarization induced by raised external potassium (120 mM), when compared to the acetylcholine response (10(-3) M), resulted in a small contraction of 19.3 +/- 4.2% in trabecular meshwork (n = 5), and of 59.0 +/- 13.7% in ciliary muscle (n = 4, P less than 0.01). Both responses were inhibited by atropine (10(-5) M). The differential potassium effect may be explained by the large number of cholinergic nerve endings in ciliary muscle as compared to trabecular meshwork tissue. Recently, a dissociation between the effects of aceclidine on outflow resistance and accommodation has been described. Our data are consistent with these observations and provide evidence for a direct role of trabecular meshwork contractility in aqueous outflow regulation.

Acetylcholine↗
PubMed1991

Transepithelial resistance of ciliary epithelial cells in culture: functional modification by protamine and extracellular calcium.

1. Bovine pigmented and human non-pigmented ciliary epithelial cells were cultured on porous filter supports to obtain measurements of transepithelial electrical parameters. 2. The non-pigmented cells showed maximal transepithelial resistance of 15-30 omega cm2 from the third to seventh day in culture. 3. The pigmented ciliary cells reached maximal resistances of 9-20 omega cm2 after the fourth day in culture. 4. The transepithelial resistances of the cultured epithelia were functionally increased by protamine. This effect could be reversed by heparin. 5. We conclude that the range of resistances in cultured ciliary epithelial cells is the same as in whole ciliary preparations. Thus, cultured ciliary epithelial cells can be used for studies on transepithelial transport.

Animals↗
PubMed1991

Endothelin-evoked contractions in bovine ciliary muscle and trabecular meshwork: interaction with calcium, nifedipine and nickel.

In the present study, we compared contractile responses of isolated bovine ciliary muscle and trabecular meshwork strips to endothelin-1 and carbachol. 1. Endothelin-1 is a potent contracting agent for ciliary muscle and trabecular meshwork. The EC50 was 5 x 10(-9) mol/l for both tissues. The maximal force evoked by endothelin was 73% of the maximal carbachol response in trabecular meshwork and 52% in ciliary muscle. 2. Carbachol contracted both tissues with an EC50 of 2 x 10(-7) mol/l. 3. In ciliary muscle, the tension was completely dependent on extracellular calcium. 4. In trabecular meshwork, 23 +/- 4% of the endothelin- and 42 +/- 10% of the carbachol-induced force response remained after removal of extracellular calcium. 5. Nifedipine (10(-5) mol/l) had only a slight relaxing effect in both tissues. 6. Nickel (10(3) mol/l) inhibited the development of force in both tissues. The relaxation induced by nickel was more pronounced in endothelin- than in carbachol-induced contractions. Different intracellular mechanisms mediating the action of endothelin and carbachol can be described: i) a calcium- and a nickel-sensitive pathway in both tissues and ii) an additional mechanism independent of external calcium in trabecular meshwork. These results indicate functional differences between the contractile region of trabecular meshwork and ciliary muscle. Endothelin may participate in accommodation and regulation of the intraocular pressure.

Animals↗
PubMed1990

[Therapy of the ocular form of Behçet disease with cyclosporin A].

Three patients with Behçet's disease and therapy-resistant posterior uveitis have been treated with cyclosporin A (CS-A) for four years. The uveitis has been controlled better, as indicated by the reduced frequency of inflammation, and there was an initial improvement in visual acuity. However, it has not been possible to prevent a slight, gradual loss of visual acuity over the years. Relapses were observed after dose reductions to blood levels below 400-500 ng/ml and following discontinuation of CS-A therapy. Few relapses occurred at higher CS-A concentrations. It was found that both types of relapse could be controlled by increasing the CS-A dose. An at least transitory increase in creatinine levels as a side effect of CS-A was observed in all patients. The authors' results and reports in the literature suggest that CS-A is an effective immunosuppressive therapy in Behçet's disease and is superior to other immunosuppressives used so far.

Adult↗
PubMed1990

Haemorheological changes in patients with retinal vein occlusion after isovolaemic haemodilution.

In 83 patients with central retinal vein occlusion and branch vein occlusion we measured the haematocrit (HCT), plasma viscosity (PV), red cell aggregation (RCA), red cell filterability (RCF) and apparent whole blood viscosity (WBV). A control group (n = 41) was matched for sex, age, and cardiovascular risk factors. Measurements were performed before and after treatment with isovolaemic haemodilution (IHD). We found no significant differences between patients with retinal vein occlusion (RVO) and control subjects in haematocrit, plasma viscosity, red cell aggregation, and red cell filterability and no increased whole blood viscosity in the patient group. Patients with ischaemic retinal vein occlusion and non-ischaemic retinal vein occlusion did not show different haemorheological parameters either. After treatment with haemodilution, only the haematocrit and whole blood viscosity were significantly decreased, and there were no changes in plasma viscosity, red cell aggregation or red cell filterability.

Adult↗
PubMed1990

[Hemorheologic parameters in patients with giant cell arteritis before and after treatment with steroids].

Basic hemorheological parameters like packed cell volume (PCV), plasma viscosity, red cell aggregation, red cell filterability and whole blood viscosity were measured in 18 patients (14 women, aged 75.4 years) with giant cell arteritis before and after treatment with steroids. The patient group was compared to controls (n = 27, age: 69.8 years) with matched age and cardiovascular risc factors. While no changes in red cell aggregation and filterability could be observed plasma viscosity was increased (1.59 +/- 0.14 mm2/s) by about 20%. The typical anemia of patients with giant cell arteritis (PVC: 0.38 +/- 0.05) prevented an increase in whole blood viscosity at high and medium shear rates (6.6 +/- 0.14 cP = mPas at 23/s). After a fortnight of systemic treatment with high doses of steroids the PCV had normalized and plasma viscosity was even lower than in controls. Thus the blood fluidity was improved as shown by a fall in whole blood viscosity (5.5 +/- 0.7 cP = mPas at 23/s). Results showed: (1) increased plasma viscosity probably induced by increased fibrinogen concentration and (2) an improvement in blood fluidity by treatment with steroids. As the plasma viscosity may participate in the deterioration of microcirculation in patients with giant cell arteritis, lowering the fibrinogen may possibly prevent a further decrease in visual acuity during the first few days of steroid treatment.

Aged↗
PubMed1990

Membrane voltage recordings in a cell line derived from human ciliary muscle.

A smooth muscle cell line (H7CM) was established from the ciliary muscle of a 1-day-old human infant. The cultured cells had a normal female karyotype (46 XX) and could be maintained in cell culture for at least 11 generations. A common feature of confluent cultures was the presence of abundant bundles of 6-7 nm microfilaments associated with dense bodies. Both the ultrastructural appearance and the presence of smooth muscle-specific alpha-isoactin (also present in the human ciliary muscle in situ) support the smooth muscle origin of the H7CM cell line. Continuous membrane voltage (Vm) recordings were obtained in confluent monolayers of H7CM cells using glass microelectrodes. Resting Vm in 105 impalements averaged -66.2 +/- 0.7 mV (mean +/- standard error of the mean). In this system, rapid membrane transients induced by changing of the superfusing test solutions were detectable. Relative K+ conductance was characterized, and the contribution of electrogenic sodium/potassium adenosine triphosphatase to Vm was investigated. Under control conditions, H7CM cells were electrically quiescent. However, action potentials could be induced by application of 10 mM barium. Barium-induced action potentials were not abolished by removal of extracellular Na+ nor were they inhibited by the presence of tetrodotoxin. However, they were blocked by verapamil, fulfilling criteria believed to be typical for smooth muscle cells. Acetylcholine, carbachol, and to a lesser extent pilocarpine induced a reversible Vm depolarization. The effect of acetylcholine was blocked by atropine, implying muscarinic receptor involvement in the Vm response. Collectively, these findings show the potential usefulness of cultured ciliary muscle cells in understanding further the cellular mechanisms underlying drug-induced contraction of the human ciliary muscle.

Acetylcholine↗
PubMed1990

[Mechanism of ascorbic acid transport in the aqueous humor].

The concentration of ascorbic acid in the aqueous humor in many species (including humans and oxen) is several times higher than the plasma concentration. The role of ascorbic acid as a protective mechanism in the intraocular tissues against light-induced damage is discussed. We have performed uptake studies using 14C-labeled ascorbic acid in cultured bovine pigmented ciliary epithelial cells in order to study the mechanisms for ascorbic acid transport from the ciliary body to the aqueous humor. We found that intracellular accumulation of ascorbic acid was Na(+)-dependent. Data from kinetic experiments suggest the presence of a co-transport system for 2 Na+ and 1 ascorbate. The oxidized form of the vitamin (dehydro-ascorbic acid, DHA) was taken up in the cell by a Na(+)-independent mechanism. Using thin-layer chromatographic assay, we found intracellularly only ascorbic acid after incubation with extracellular DHA, indicating the presence of DHA reductase activity in ciliary body epithelial cells. Thus, these cells possess two mechanisms for intracellular accumulation of ascorbic acid: (1) co-transport for 2 Na+ and 1 ascorbate and (2) a Na(+)-independent DHA transport in cooperation with intracellular DHA reductase. These mechanisms could be involved in the transport of ascorbic acid from the stroma to the aqueous humor.

Animals↗
PubMed1989

Endothelin depolarizes membrane voltage and increases intracellular calcium concentration in human ciliary muscle cells.

The ciliary muscle which is involved in accommodation and regulation of aqueous humour outflow resistance resembles smooth muscle in other parts of the body. In the present investigation we used an established primary cell line (H7CM) to study the effects of endothelin, a novel vasoconstrictor peptide, on membrane voltage (V) and intracellular calcium in cultured human ciliary muscle cells. Membrane voltage was measured in confluent monolayers of H7CM cells using conventional microelectrodes. Intracellular calcium concentration [( Ca]i) was measured in single H7CM cells using the fluorescent calcium indicator fura-2. Under resting conditions V averaged -66.9 +/- 0.7 mV (mean +/- SEM, n = 125). Endothelin (10(-10)-10(-6)M) induced a dose-dependent reversible membrane voltage depolarization and a dose-dependent rise in [Ca]i. The initial calcium peak was followed by a recovery phase during which oscillations of [Ca]i occurred. The initial calcium peak was not dependent on the presence of extracellular calcium and was not abolished in the presence of the calcium antagonist verapamil (10(-4)M). Thus it is probably mediated by a release of calcium from intracellular reservoirs. We conclude that cultured human ciliary muscle cells express a functional endothelin receptor.

Benzofurans↗