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Biomedical subjects

B Lindemann

Publications and source records attributed to B Lindemann.

At least 73 records · Page 4Linked to original sources
PubMed1983

Chemical stimulation of Na transport through amiloride-blockable channels of frog skin epithelium.

The stimulation of apical Na permeability caused by a number of reagents effective from the outer side of the membrane was investigated by fluctuation analysis. In the epidermis of R. ridibunda, parachloromercuriphenyl sulfonate (PCMPS) and benzimidazolyl guanidine (BIG) increase the number (N0) of conducting Na channels by releasing channels from Na self-inhibition. As a consequence, the apparent macroscopic affinity for amiloride is increased. 5-dimethyl amiloride and trinitrobenzene sulfonate (TNBS) also cause reversible stimulation by increasing N0; here release from self-inhibition is less clear. With each of the four stimulators investigated, the Na channel current remained unaffected or was only marginally increased. In addition to its stimulatory effect, TNBS caused irreversible blockage of Na channels. Apart from their stimulatory effects, BIG and 5-dimethyl amiloride, both of which have a side-chain terminated with an amidino group, are high rate-blocking competitors of amiloride.

4-Chloromercuribenzenesulfonate↗
PubMed1982

The role of sodium-channel density in the natriferic response of the toad urinary bladder to an antidiuretic hormone.

Urinary bladders of Bufo marinus were depolarized, by raising the serosal K concentration, to facilitate voltage-clamping of the apical membrane. Passive Na transport across the apical membrane was then studied with near-instantaneous current-voltage curves obtained before and after eliciting a natriferic response with oxytocin. Fitting with the constant-field equation showed that the natriferic effect is accounted for by an increase in the apical Na permeability. It is accompanied by a small increase in cellular Na activity. Furthermore, fluctuation analysis of the amiloride-induced shot-noise component of the short-circuit current indicated that the permeability increase is not due to increased Na translocation through those Na channels which were already conducting prior to hormonal stimulation. Rather, the natriferic effects is found to be based on an increase in the population of transporting channels. It appears that, in response to the hormone, Na channels are rapidly "recruited" from a pool of electrically silent channels.

Animals↗
PubMed1982

Aldosterone control of the density of sodium channels in the toad urinary bladder.

Near-instantaneous current-voltage relationships and shot-noise analysis of amiloride-induced current fluctuations were used to estimate apical membrane permeability to Na (PNa), intraepithelial Na activity (Nac), single-channel Na currents (i) and the number of open (conducting) apical Na channels (N0), in the urinary bladder of the toad (Bufo marinus). To facilitate voltage-clamping of the apical membrane, the serosal plasma membranes were depolarized by substitution of a high KCl (85 mM) sucrose (50 mM) medium for the conventional Na-Ringer's solution on the serosal side. Aldosterone (5 X 10(-7) M, serosal side only) elicited proportionate increases in the Na-specific current (INa and in PNa, with no significant change in the dependence of PNa on mucosal Na (Nao). PNa and the control of PNa by aldosterone were substrate-dependent: In substrate-depleted bladders, pretreatment with aldosterone markedly augmented the response to pyruvate (7.5 X 10(-3) M) which evoked coordinate and equivalent increases in INa and PNa. The aldosterone-dependent increase in PNa was a result of an equivalent increase in the area density of conducting apical Na channels. The computed single-channel current did not change. We propose that, following aldosterone-induced protein synthesis, there is a reversible metabolically-dependent recruitment of preexisting Na channels from a reservoir of electrically undetectable channels. The results do not exclude the possibility of a complementary induction of Na-channel synthesis.

Aldosterone↗
PubMed1982

Dependence of ion flow through channels on the density of fixed charges at the channel opening. Voltage control of inverse titration curves.

Model calculations were done to investigate the effect of titratable fixed charges at channel openings on ion flow through open channels. The current titration curves (channel current vs. bulk pH) can assume the shape expected from the change of the ionic surface concentration with pH (c-control), or be inverted, i.e., follow the change of the electrical field within the membrane (V-control). The relationships were explored pars pro toto for Goldman-Hodgkin-Katz channels, two-barrier one-site channels and six-barrier five-site channels. With net current flowing in the direction of the concentration gradient and from the titrated fixed charge layer into the channel, c-control is the sign of low channel occupancy (entrance-step limitation) and V-control the sign of high channel occupancy (exit-step limitation). At intermediate occupancy, the current titration curve can be nearly invariant to pH.

Animals↗
PubMed1980

Current-voltage analysis of apical sodium transport in toad urinary bladder: effects of inhibitors of transport and metabolism.

The basal-lateral surface of the epithelium of the urinary bladder of the toad (Bufo marinus) was depolarized by exposure of the serosal surface to 85 mM KCL and 50 mM sucrose. The extent of depolarization appeared to be virtually complete, as evaluated by the invariance in the transepithelial electrical potential difference and conductance on addition of nystatin (a monovalent cation ionophore) to the serosal medium. The Na-specific current (INa) was defined as the current sensitive to the removal of Na from the mucosal medium or inhibitable by addition of amiloride to this medium. In the presence of the high K-sucrose serosal medium, rapid, serial, stepwise clamping of the transepithelial voltage (V) yielded a curvilinear dependence of INa on V; which is taken to represent the I--V curve of the apical Na channels. The constant field equation (Goldman, D.E. 1943; J. Gen. Physiol. 27:37) fits the I--V data points closely, allowing estimates to be made of the permeability to Na of the apical membrane (PNa) and of the intracellular Na activity (Nac). Exposure of the apical surface to amiloride (5 X 10(-7) M) decreased PNa in proportion to the decrease in INa (i.e., approximately 70%) but decreased Nac only 25%. In contrast, an equivalent reduction in INa elicited by exposure of the basal-lateral surface to ouabain was accompanied by only a 20% decrease in PNa and a sixfold increase in Nac. The effects of amiloride on PNa and ouabain on Nac are consistent with the primary pharmacological actions of these drugs. In addition, PNa appears to be under metabolic control, in that 2-deoxyglucose, a specific inhibitor of glycolysis, decreased INa and PNa proportionately, and lowered Nac marginally, effects indistinguishable from those obtained with amiloride.

Amiloride↗
PubMed1980

In vitro investigations on the action fosfomycin alone and in combination with other antibiotics on Pseudomonas aeruginosa and Serratia marcescens.

86.4% of the Pseudomonas aeruginosa and 91% of the Serratia marcescens strains were sensitive to fosfomycin. In combination with mezlocillin, cefoxitin, gentamicin and nalidixic acid a synergistic action was detected against these bacterial strains. It was most marked in the combination fosfomycin/nalidixic acid against Serratia marcescens. An acceleration of the fosfomycin action on the bacterial cells and the speed of bacteriolysis was observed in weakly acid medium (pH 6.0), in the presence of 10% active human serum and with increasing glucose-6-phosphate concentrations in the test medium. There is no parallel resistance between gentamicin and fosfomycin against Pseudomonas aeruginosa.

Anti-Bacterial Agents↗
PubMed1978

Volume changes and potential artifacts of epithelial cells of frog skin following impalement with microelectrodes filled with 3 m KCl.

Cells of isolated frog skin epithelium were observed microscopically during impalement with standard microelectrodes of 5 to 20 Momega resistance, filled with 3 m KCl. Impaled cells, as well as some neighboring cells, were seen to swell 10 to 100 sec after impalement, while the negative potential recorded by the microelectrode depolarized (open circuit conditions). Apparently, osmotic swelling of small epithelial cells may be caused by diffusion of KCl from such electrodes. This conclusion is supported by calculations quoted from the literature of KCl loss from microelectrodes. Intracellular recordings from epithelia with destructed cellular membranes gave negative "pre-tip potentials" of up to mV. The potentials could be altered by electrode movement, by decreasing the ambient pH or the tip-pH and by modifying the fixed charges of the tissue chemically. It is shown that even a moderate loss of KCl, which will not result in appreciable swelling, can produce negative potentials in front of the electrode tip if the protoplasm has a high density of negative fixed charges. We suggest the use of 3 m KCl electrodes with resistances above 30 Momega if after impalement compression of intracellular material by the tip can be avoided. Where such compression cannot be avoided, it is best to fill the microelectrode with an isotonic solution which mimics the electrolyte composition of the cytosol.

Animals↗
PubMed1978

Instrumentation and specimen preparation for electron beam X-ray microanalysis of frozen hydrated bulk specimens.

A cooling chain for the handling of frozen hydrated bulk specimens is described. Use of this method permits the specimen to be kept fully hydrated. After quench freezing, the specimen is transferred to a freeze etch apparatus, freeze fractured, carbon coated and transferred onto the precooled cold stage of the SEM by means of an airlock. The specimen is examined in the secondary electron mode and analysed using an energy dispersive X-ray analyser. The midgut of Chironomus thummi larvae and frog skin epithelium were used to test the performance.

Animals↗
PubMed1977

Sodium-specific membrane channels of frog skin are pores: current fluctuations reveal high turnover.

The reversible sodium transport blocker amiloride causes current fluctuations at the apical membrane of the outer stratum granulosum of frog skin. Their power density spectra reveal that single transport sites translocate more than 10(6) sodium ions per second, which indicates a pore mechanism. The density of open plus amiloride-blocked pores is in the order of 10(8) pores per square centimeter of skin area with 60 millimolar sodium and 18 micromolar amiloride in the outer solution.

Amiloride↗
PubMed1977

Current-voltage curve of sodium channels and concentration dependence of sodium permeability in frog skin.

1. The inward facing membranes of in vitro frog skin epithelium were depolarized with solutions of high K concentration. The electrical properties of the epithelium are then expected to be governed by the outward facing, Na-selective membrane.2. In this state, the transepithelial voltage (V) was clamped to zero and step-changes of Na activity in the outer solution ((Na)(o)) were performed with a fast-flow chamber at constant ionic strength, while the short-circuit current was recorded.3. At pre-selected times after a step-change of (Na)(o) the current response (I) to a fast voltage staircase was recorded. This procedure was repeated after blocking the Na channels with amiloride to obtain the current-voltage curve of transmembrane and paracellular shunt pathways. The current-voltage curve of the Na channels was computed by subtracting the shunt current from the total current.4. The instantaneous I(Na)-V curve thus obtained at a given (Na)(o) could easily be fitted with the constant field equation in the range between -50 and zero mV. This fit yielded approximate estimates of P(Na), the Na- permeability of the Na-selective membrane (at this (Na)(o)) and the cellular Na activity, (Na)(c). As residual properties of the serosal membrane were ignored the computed values are expected to underestimate the true ones.5. At constant (Na)(c), the steady-state value of 1/P(Na) increases linearly with (Na)(o). Error analysis and the effect of drugs show that the dependence is not due to the residual properties of the inward facing membranes but reflects the true behaviour of P(Na).6. The steady-state P(Na) at a given (Na)(o) is smaller than the transient P(Na) observed right after a stepwise increase of (Na)(o) to this value. The time constant of P(Na)-relaxation is in the order of seconds.7. In conclusion, Na transport through open Na-selective channels of the outward facing membrane of the stratum granulosum cells can be described as an electrodiffusion process which as such does not saturate with increasing (Na)(o). However, when added to the outer border of the membrane Na causes a decrease of P(Na) within several seconds. It is considered that binding of Na results in closure of Na channels.

Amiloride↗
PubMed1976

[Rise in neutrophils after hydrocortisone seen as bone marrow reserve mass. Dependency on spleen size].

In 25 patients with a wide range of postmitotic marrow neutrophil mass a linear relationship was observed between the number of postmitotic marrow neutrophils and the rise of blood neutrophils after intravenous injection of 3 mg hydrocortisone/kg. Related to marrow neutrophil cellularity, the response curve was significantly higher in 10 splenectomized patients but greatly depressed in 10 patients with splenomegaly.

Bone Marrow↗