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D Wolff

Publications and source records attributed to D Wolff.

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

Ion channels from the Bacillus subtilis plasma membrane incorporated into planar lipid bilayers.

Fusion of Bacillus subtilis plasma membrane vesicles with planar lipid bilayers induced the appearance of discrete current fluctuations characteristic of ion channels. These channels showed a wide range of conductances and kinetic behaviors. In 300 mM KCl, their conductances ranged from a few hundreds of pS to more than 1 nS, and most of them exhibited several sub-states. The channels poorly discriminated between small univalent anions and cations. Some of them showed voltage dependence and most of them presented a complex gating kinetics. The results are consistent with the hypothesis of the presence in the B. subtilis plasma membrane of pores composed of subunits that function cooperatively.

Bacillus subtilis↗
PubMed1992

The major Thiobacillus ferrooxidans outer membrane protein forms low conductance ion channels in planar lipid bilayers.

A protein isolated and purified from the outer membrane of the acidophilic, chemolithotrophic bacterium, Thiobacillus ferrooxidans with an oligomeric molecular weight of 90,000 Da (p90) was incorporated into phosphatidylethanolamine planar lipid bilayers. The protein formed slightly anionic channels in KCl solutions, with a conductance of 25 pS in 100 mM KCl. The current-voltage relationship was linear between +/- 60 mV, and the conductance was a saturating function of the salt concentration. These channels fluctuated from a single open to closed state at low potentials, but present flickering activity at higher potentials.

Bacterial Outer Membrane Proteins↗
PubMed1991

Proton modulation of a Ca(2+)-activated K+ channel from rat skeletal muscle incorporated into planar bilayers.

The effect of pH on the activation of a Ca-activated K+ [K(Ca)] channel from rat skeletal muscle incorporated into planar lipid bilayers was studied. Experiments were done at different intracellular Ca2+ and proton concentrations. Changes in pH modified channel kinetics only from the Ca-sensitive face of the channel. At constant Ca2+ concentration, intracellular acidification induced a decrease in the open probability (Po) and a shift of the channel activation curves toward the right along the voltage axis. The displacement was 23.5 mV per pH unit. This displacement was due to a change in the half saturation voltage (Vo) and not to a change in channel voltage dependence. The shifts in Vo induced by protons appeared to be independent of Ca2+ concentration. The slope of the Hill plot of the open-closed equilibrium vs. pH was close to one, suggesting that a minimum of one proton is involved in the proton-driven channel closing reaction. The change in Po with variations in pH was due to both a decrease in the mean open time (To) and an increase in the mean closed time (Tc). At constant voltage, the mean open time of the channel was a linear function of [Ca2+] and the mean closed time was a linear function of 1/[Ca2+]2. Changes in the internal pH modified the slope, but not the intercept of the linear relations To vs. [Ca2+] and Tc vs. 1/[Ca2+]2. On the basis of these results an economical kinetic model of the effect of pH on this channel is proposed. It is concluded that protons do not affect the open-closed reaction, but rather weaken Ca2+ binding to all the conformational states of the channel. Moreover, competitive models in which Ca2+ and H+ cannot bind to the same open or closed state are inconsistent with the data.

Animals↗
PubMed1991

[Unusual tumors of the testis. Apropos of 22 cases].

The authors report their experience of rare non-germ-cell tumours of the testis over a period of 10 years. The criteria of benign disease, justifying testicular preservation in 5 out of 7 cases of epidermoid cysts, are defined. Four cases of Leydig cell tumours, including 3 with gynaecomastia, are described. Three cases of adenomatoid tumours with conservative surgery, 3 lymphomas, 2 mature teratomas and 2 cysts of the rete testis are also reported. The place of ultrasonography is defined and the possibility of conservative surgery is discussed in relation to a review of the recent literature.

Adult↗
PubMed1990

[Physiopathology of cystic fibrosis].

Cystic Fibrosis (CF) is the most common lethal genetic autosomic disease in Caucasians. The disease expresses itself in airway and other epithelial cells as a defective chloride ion absorption and secretion. At least, an abnormal cAMP-dependent regulation of an apically located chloride channel has been proposed as the underlying molecular defect. The gene responsible for CF has been identified and predicted to encode a membrane protein termed cystic fibrosis transmembrane conductance regulator (CFTR). The functional role of the predicted protein remains unclear, although strong evidence suggest that it is directly or indirectly involved in regulation of the apical chloride permeability in epithelial cells. This review discusses the fundamental issues currently being investigated in CF.

Bucladesine↗
PubMed1988

Charybdotoxin blocks with high affinity the Ca-activated K+ channel of Hb A and Hb S red cells: individual differences in the number of channels.

We have investigated the effect of a purified preparation of Charybdotoxin (CTX) on the Ca-activated K+ (Ca-K) channel of human red cells (RBC). Cytosolic Ca2+ was increased either by ATP depletion or by the Ca ionophore A23187 and incubation in Na+ media containing CaCl2. The Ca-K efflux activated by metabolic depletion was partially (77%) inhibited from 15.8 +/- 2.4 mmol/liter cell.hr, to 3.7 +/- 1.0 mmol/liter cell.hr by 6 nM CTX (n = 3). The kinetic of Ca-K efflux was studied by increasing cell ionized Ca2+ using A23187 (60 mumol/liter cell), and buffering with EGTA or citrate; initial rates of net K+ efflux (90 mmol/liter cell K+) into Na+ medium containing glucose, ouabain, bumetanide at pH 7.4 were measured. Ca-K efflux increased in a sigmoidal fashion (n of Hill 1.8) when Ca2+ was raised, with a Km of 0.37 microM and saturating between 2 and 10 microM Ca2+. Ca-K efflux was partially blocked (71 +/- 7.8%, mean +/- SD, n = 17) by CTX with high affinity (IC50 0.8 nM), a finding suggesting that is a high affinity ligand of Ca-K channels. CTX also blocked 72% of the Ca-activated K+ efflux into 75 mM K+ medium, which counteracted membrane hyperpolarization, cell acidification and cell shrinkage produced by opening of the K+ channel in Na+ media. CTX did not block Valinomycin-activated K+ efflux into Na+ or K+ medium and therefore it does not inhibit K+ movement coupled to anion conductive permeability. The Vmax, but not the Km-Ca of Ca-K efflux showed large individual differences varying between 4.8 and 15.8 mmol/liter cell.min (FU). In red cells with Hb A, Vmax was 9.36 +/- 3.0 FU (mean +/- SD, n = 17). The Vmax of the CTX-sensitive, Ca-K efflux was 6.27 +/- 2.5 FU (range 3.4 to 16.4 FU) in Hb A red cells and it was not significantly different in Hb S (6.75 +/- 3.2 FU, n = 8). Since there is larger fraction of reticulocytes in Hb S red cells, this finding indicates that cell age might not be an important determinant of the Vmax of Ca-K+ efflux. Estimation of the number of CTX-sensitive Ca-activated K+ channels per cell indicate that there are 1 to 3 channels/per cell either in Hb A or Hb S red cells. The CTX-insensitive K+ efflux (2.7 +/- 0.9 FU) may reflect the activity of a different channel, nonspecific changes in permeability or coupling to an anion conductive pathway.

Calcium↗
PubMed1987

Diffusivity of 125I-labelled macromolecules through collagen: mechanism of diffusion and effect of adsorption.

Diffusion of angiotensin II, albumin and aldolase was studied through collagen membranes with swelling ratios between 4 and 15. The diffusion coefficient was measured from the time-lag for the onset of steady-state flux through the membrane. Binding of macromolecules to collagen was evaluated from the results of sorption studies conducted as a function of macromolecular concentration. Results presented indicate that the diffusion of macromolecules through collagen membrane is slowed by electrostatic and hydrogen bonding between individual macromolecular chains and collagen. The extent of adsorption is increased as the molecular weight of the diffusant increases. Diffusion of water soluble macromolecules through collagen occurs rapidly, suggesting that diffusion occurs through water filled channels as opposed to between collagen molecules. The results of these studies are useful in understanding diffusion through connective tissues and in the design of drug delivery systems based on collagen.

Adsorption↗
PubMed1987

Mechanisms of Cs+ blockade in a Ca2+-activated K+ channel from smooth muscle.

Large unitary conductance Ca2+-activated K+ channels from smooth muscle membrane were incorporated into phospholipid planar bilayers, and the blockade induced by internally and externally applied Cs+ was characterized. Internal Cs+ blockade is voltage dependent and can be explained on the basis of a Cs+ binding to a site that senses 54% of the applied voltage, with an apparent dissociation constant, Kd(0), of 70 mM. On the other hand, external Cs+ blocks the channel in micromolar amounts, and the voltage dependence of blockade is a function of Cs+ concentration. The fractional electrical distance can be as large as 1.4 at 10 mM Cs+. This last result suggests that the channel behaves as a multi-ion pore. At large negative voltages the I-V relationships in the presence of external Cs+ show an upturn, indicating relief of Cs+ block. External Cs+ blockade is relieved by increasing the internal K+ concentration, but can be enhanced by increasing the external K+. All the characteristics of external Cs+ block can be explained by a model that incorporates a "knock-on" of Cs+ by K+.

Animals↗
PubMed1987

A cage for the ferret.

A cage for ferrets is described that consists of a plastic box with a metal sliding-grill top and metal front lattice. It contains a new feeding system using dishes that can be removed without opening the cage. The cages are kept in mobile racks and are commercially available.

Animals↗
PubMed1986

Studies on epidemiology and pathogenicity of porcine circovirus.

Antibodies to porcine circovirus (PCV) which is the smallest animal virus known so far were found in 77-95 per cent of sera from slaughter pigs gathered in Berlin and two districts of Northern Germany. About 60 per cent of these positive sera had relatively high titres similar to those in experimentally infected pigs 3-6 weeks after infection. This indicates that the animals might have become infected during the fattening period. Sera from 2-3 year old pigs from a laboratory animal breeding institution were also found positive (83 per cent) but titres were lower. Experimentally infected minipigs developed antibodies and virus was isolated from nasal swabs and from fecal samples. The animals neither showed any signs of illness nor were pathological changes noticable. The assumption that PCV is a common virus in all swine populations was strengthened by the finding of PCV antibodies in wild boars shot in the forests of the Berlin region.

Animals↗
PubMed1986

Large cation-selective pores from rat liver peroxisomal membranes incorporated to planar lipid bilayers.

Fusion of a highly purified fraction of rat liver peroxisomal membranes to planar lipid bilayers incorporates large, cation-selective voltage-dependent pores. The PK/PCl ratio of these pores, estimated in KCl gradients, is close to 4. The pores display several conductance states and spend most of the time open at voltages near 0 mV, closing at more positive and negative voltages. At voltages near 0 mV the most frequent open state has a conductance of 2.4 nS in 0.3 M KCl. At voltages more positive and more negative than 10 mV the most frequent open state displays a conductance of 1.2 nS in 0.3 M KCl. With these results pore diameters of 3 and 1.5 nm, respectively, can be estimated. We suggest that these pores might account for the unusually high permeability of peroxisomes to low molecular weight solutes. Fusion also incorporates a perfectly anion-selective, two-open states channel with conductances of 50 and 100 pS in 0.1 M KCl.

Animals↗
PubMed1986

Characterization of a calcium-activated potassium channel from rabbit intestinal smooth muscle incorporated into planar bilayers.

Interaction of vesicles from a microsomal fraction of rabbit intestinal smooth muscle with planar bilayers promotes the incorporation of a large conductance potassium-selective channel. The channel conductance fluctuates between two states: closed and open and the fraction of time the channel dwells in the open state is a function of the electric potential difference and the calcium concentrations. This channel seems to correspond to a Ca-activated K channel described by other authors in smooth muscle cells with the patch-clamp technique. Single-channel conductance is a saturating function of the potassium concentration. The relationship between conductance and concentration cannot be described by a hyperbolic function, suggesting multiple occupancy of the channel. The single-channel conductance is 230 pS in symmetrical 0.1 M KCl. Current is a linear function of the applied voltage in the range between -100 and +100 mV, at concentrations of 0.1 M KCl or higher. At lower concentrations, current-to-voltage curves bend symmetrically to the voltage axis. Sodium, lithium and cesium ions do not pass through the channel and the permeability for Rb is 66% that of potassium. All these alkali cations and Ca2+ block the channel in a voltage-dependent manner. A two-site three-barrier model on Eyring absolute reaction rate theory can account for the conduction and blocking characteristics.

Animals↗
PubMed1986

Diffusivity of 125I-calmodulin through collagen membranes: effect of source concentration and membrane swelling ratio.

Diffusivity of 125I-calmodulin (MW congruent to 17,000) through collagen membranes was studied as a model for the release of macromolecules from collagen matrices. The diffusion coefficient of calmodulin through collagen membranes was determined from time-lag experiments conducted in a dialysis cell at 24 degrees C. Based on time-lag experiments, the diffusion coefficient was observed to be a function of source concentration and membrane swelling ratio after denaturation. The dependence of the diffusion coefficient on source concentration was consistent with a model involving calmodulin immobilization by the collagen membrane. At high source concentrations the diffusion coefficient of calmodulin through collagen membranes was observed to vary from about 10(-8) for uncrosslinked membranes to 10(-9) cm2/s for highly crosslinked membranes. Based on theoretical calculations, the release rate from collagen matrices may be altered by a factor of three. It was concluded that the release rate of biologically active molecules from collagen matrices can be controlled by varying the extent of crosslinking and the macromolecular concentration. Further studies are necessary to characterize the release of other macromolecules from collagen matrices.

Animals↗
PubMed1985

Adsorption of uni and divalent cations to planar bilayer membranes containing sulphatides or phosphatidylserine.

It has been postulated that sulphatides may be the K+ binding site of the sodium pump. In order to test this hypothesis we studied the binding of K+ to bilayer membranes containing sulphatides or phosphatidylserine. The adsorption constants of Na+, K+ and Ca2+ to planar bilayers containing these acidic lipids were determined from changes in the electrostatic potential at the membrane surface. Our results indicate that univalent cations adsorb weakly to both lipids and Ca2+ binds more strongly. The sequence of ion binding was Ca2+ greater than Na+ greater than K+. These results indicate that K+ does not bind specifically to sulphatides or phosphatidylserine and rule out the proposal that sulphatides by themselves provide the K+ binding site of the sodium pump.

Calcium↗
PubMed1983

Somatic hybridization of two selected single cells.

Two single mesophyll-protoplasts of Nicotiana tabacum cv. xanthi were selected into a 100 nl microdroplet of 0.4 M mannitol. Two cylindrical platinum electrodes were inserted into the microdroplet to align the two single cells via dielectrophoresis in an AC-field (1 MHz, about 120 V X cm-1). A single square DC-pulse of about 1.5 KV X cm-1 was applied to induce protoplast fusion.

Cell Fusion↗