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Biomedical subjects

K Janácek

Publications and source records attributed to K Janácek.

At least 19 recordsLinked to original sources
PubMed2000

Osmosis: membranes impermeable and permeable for solutes, mechanism of osmosis across porous membranes.

A mathematical description is presented of osmotic flows across both ideally semipermeable membranes and membranes permeable not only for the solvent but also for the solute. The principles of thermodynamics of irreversible processes used for the description are given and illustrated on the example of electroosmosis. Modern ideas about the physical basis of osmotic pressure on porous membranes are discussed and an experiment is described that models the processes of osmosis on a macroscopic level.

Membranes↗
PubMed1999

[Determination of chlorine levels in Presept, a modern disinfectant].

Presept (containing sodium dichloroisocyanurate as active component) was shown to be an excellent analytical reagent superior to classical Chloramine T and Chloramine B. Potentiometric titration of potassium ferrocyanide was found to be most suitable for estimation of chlorine content in Presept solutions. The presence of serum albumin can block or reverse the oxidation of ferrocyanide completely, whereas that of a detergent is of little importance. The content of available chlorine in various Presept tablets was found to be as a rule slightly higher than that guaranteed by the dilution rules of Johnson & Johnson. Presept solutions are remarkably stable, paradoxically the concentration of available chlorine in open vessels remains higher than in perfectly closed vessels.

Chlorine↗
PubMed1997

Cell volume regulation in Claviceps fusiformis. An animal-type Na,K-ATPase operating in a fungus?

Claviceps fusiformis, an ergot pathogen of pearl millet, was equilibrated in media without and with 0.1 mM ouabain (g-strophantin). Highly significant effects of ouabain on the contents of sodium ions and water were found, suggesting that an active transport of sodium ions, similar to that in animal cells, regulates the cell volume of the fungus. The basic role of the sodium pump appears to be to decrease larger cell volumes and to increase the small ones; for this purpose it can even reverse its direction.

Biological Transport, Active↗
PubMed1997

Characterization of phosphate transport in Streptomyces granaticolor.

Transport of inorganic phosphate in Streptomyces granaticolor was characterized in two growth stages; kinetic parameters were determined and two transport systems were found in both stages, with the following values: KT1 = 0.06 mM, Jlim1 = 0.95 nmol min-1 (mg DS)-1, and KT2 = 1.80 mM, Jlim2 = 25 nmol min-1 (mg DS)-1. Both systems require metabolic energy and substrates, such as sugars or polyols; when alanine was used or the energy source was omitted, the kinetic parameters changed in both systems. Both systems were inhibited by the ionophore cccp with identical k(i). KCN, an inhibitor or terminal cytochrome oxidase, inhibited the uptake of phosphate only partially, the uptake was inhibited completely when also the inhibitor of the alternative oxidative pathway (salicylhydroxamic acid) was added. Antimycin A inhibited the uptake completely. Arsenate inhibited competitively.

Antimycin A↗
PubMed1996

Ba2+ ions hyperpolarize algal cell membrane and enhance plasmalemma resistance without affecting ion and water contents.

Culturing the fresh-water alga Hydrodictyon reticulatum for 9 days in the presence of 0.2 and 0.4 mmol/l Ba2+ increases the membrane potential about twice and the plasmalemma resistance 5-10 times without having any significant effect on the cell contents of water and Na+, K+ and Cl- ions. While in control cells the membrane potential is determined by the diffusion potential of K+, in Ba(2+)-treated cells the factor determining membrane potential and resistance is the unequal distribution of protons across the membrane.

Barium↗
PubMed1987

Parallel pathways of potassium transport in the alga Hydrodictyon reticulatum. Effects of calcium.

Inflow of potassium ions into the alga Hydrodictyon reticulatum is reduced in the dark, the reduction being accompanied by a change in the selectivity pattern with respect to alkali metal ions, observed in competition experiments and evaluated by the gnostic analysis as described by Kovanic. This suggests that in the light a special mechanism of potassium uptake with a characteristic selectivity is switched on. This mechanism can be also suppressed by too high (2 mmol/l) or too low (EGTA) concentration of calcium ions in the medium. Since the same applies to the light-induced alkalinization of the algal surroundings it seems that the light-induced potassium uptake is related to the light-induced alkalinization, e.g., via exchange of external potassium cations for intracellular protons.

Biological Transport, Active↗
PubMed1987

Effects of amiloride on the transport of sodium and other ions in the alga Hydrodictyon reticulatum.

The diuretic amiloride, an almost specific inhibitor of sodium transport in animal cells and tissues, appears to produce a number of effects in the alga Hydrodictyon reticulatum. At 1 mmol/l concentration it markedly reduces the influx of sodium ions (but not their active outflux), the influxes of potassium, chloride as well as of bicarbonate ions, and causes a profound decrease in the plasmalemma membrane potential. This plurality of inhibitory effects suggests that individual transport processes in the alga are mutually coupled.

Amiloride↗
PubMed1986

Cell volume maintenance and regulation in kidney tissues of various vertebrates.

Ouabain-sensitive and ouabain-insensitive mechanisms are shown to participate to a different extent in the cell volume maintenance in kidney tissues of various vertebrates. The ouabain-insensitive mechanisms predominate in the lamprey and in fresh-water fishes, whereas in the flounder, representing sea fishes, there is a complete predominance of the ouabain-sensitive mechanism. In the rabbit kidney cortex tissue the two systems play a comparable role. Analogous inter-species differences are displayed when the cells regulate their volume in anisoosmolar media.

Animals↗
PubMed1984

Some characteristics of urea accumulation in the renal cortex tissue of rats and dogs.

The urea concentration in the renal cortex ([RC]), liver ([L]) and skeletal muscle ([SM]) of non-diuretic Wistar rats was measured chemically and after an i.m. injection of 14C-urea and was compared with the plasma urea concentration ([P]). [L]/[P] and [SM]/[P] always equalled 1, irrespective of whether they were measured chemically or by means of radioactivity. [RC]/[P] was 2.81, again without any difference between chemical and radioactive measurement. The ratio of the chemically measured urea concentration in the renal cortex and plasma of mongrel dogs was 5.71, i.e. significantly higher than in rats (p less than 0.01). The intrarenal infusion of KCN, iodoacetate and ouabain did not alter it significantly (5.52, p greater than 0.05). Active transport, in whatever form, does not seem to be the cause of the high urea concentration in rat and dog renal cortex.

Animals↗
PubMed1984

Effect of a sudden and a slow concentration increase in plasma urea on its concentration in some tissues of the dog and rat.

The urea concentration in the renal cortex ([RC]) of pentobarbital-anaesthetized dogs was 5.71 times higher than the plasma concentration ([P]); the liver ([L]) and the skeletal muscle ([SM]) concentrations were the same as ([P]). Rapid infusion of 20% urea (1 g/kg b.w. within 1 min) was followed by a sudden increase in [P]; [RC] and [L] rose to values nonsignificantly different from [P] and remained non-significantly different for the whole 4 hours of the experiment; at the end, [P] was still about 10 times higher than before infusion. Surprisingly, [SM] 2 and 6 min after infusion was significantly lower than [P]; later they were the same. The experiment thus does not testify to the existence of active transport of urea in the RC. The permeability of the skeletal muscle membrane for urea is lower than that of the RC and liver. Chronic uraemia was induced in rats by transplanting the trigonum vesicae into the peritoneal cavity. In addition to the chemical determination of urea, 14C-urea (marked*) was also measured. [RC]/[P] and [RC*]/[P*] fell as [P] rose; [L], [L*] [SM] and [SM*] never differed from [P] or [P*]. Fluid [PF] collected in the peritoneal cavity had the same chemically determined and radioactive urea concentration as P, but it was hypoosmolar and had a lower [Na+] than P. These experiments likewise did not testify to active urea transport in the RC. It is not clear what caused the osmolarity and sodium gradient between the PF and P, but the peritoneal wall definitely did not act as a simple dialyzing membrane.

Animals↗
PubMed1983

Cell water content in carp kidney tissue slices as influenced by various osmotic agents.

Determination of water content in the surviving kidney tissue of the carp (Cyprinus carpio) is a convenient method for studying epithelial cell volume regulation under the influence of various osmotic agents and inhibitors. Artificial media of abnormal tonicities were used both as a purely experimental tool and as an attempt to model the behaviour of the tissue under extreme (physiological or pathological) conditions. In a medium hypertonic with mannitol the inhibition of the sodium-potassium pump by ouabain does not change the water content of the tissue (the same as in normal Krebs-Henseleit saline). On the other hand, in media which are hypotonic or hypertonic by addition of NaCl, KCl, Tris chloride or sodium benzenesulphonate the same inhibition invariably results in an increased water content. Thus, in contrast to the situation in normal or mannitol-hypertonic media, the ouabain-sensitive sodium-potassium pump does regulate the cell volume in artificial salines which are hypotonic or hypertonic by addition of electrolytes. 2,4-dinitrophenol often brings about a more pronounced swelling of the tissue than ouabain, suggesting the presence of an additional cell-volume regulating mechanism, ATP-dependent but ouabain-insensitive. The additional swelling is not always accompanied by a gain of sodium; hence it may not be correct to call the above mechanism a "second sodium pump". On the whole, the carp kidney tissue appears to behave as an osmometer with a certain incompressible volume, gaining or losing either sodium or potassium chloride in various abnormal media or with the two above inhibitors.

2,4-Dinitrophenol↗
PubMed1982

Ouabain-insensitive mechanism of cell volume maintenance in the carp kidney.

1) An ouabain-insensitive mechanism of cell volume maintenance, similar to that operating in the kidney tissue of mammals and in epithelial cells of the frog urinary bladder, has been demonstrated in the kidney tissue of carp (Cyprinus carpio)--there is no significant swelling even after 4-hour incubation with 10(-4) mol/l-1 ouabain. 2) The mechanism is not affected by 2-hour incubation with sodium in the saline replaced with tris or choline and, unlike in rabbit kidney cortex, cannot be inhibited by alkaline pH. 3) Neither a contractile mechanism sensitive to cytochalasin B, nor transport of divalent cations could be shown to be involved in this ouabain-insensitive cell volume maintenance in the carp kidney tissue.

Animals↗
PubMed1980

Effect of Mercurascan on sodium transport in frog skin and bladder.

The authors studied the effect of Mercurascan (MSC) (a hydroxy- mercury derivative of fluorescein) on electrical parameters, namely potential difference (P.D.) and short circuit current (S.C.C.) of frog skin and on the ability of frog bladder tissue to accumulate sodium ions in experiments in vitro. It was found that MSC, in 10(-4) mol/l concentration, reduced the S.C.C., after a brief initial increase, to 5% of the original value and that the P.D. fell steadily right from the outset. In 10(-5) mol/l concentration it raised the S.C.C. by 60% and the increase lasted several hours. The P.D. was unaffected. In 10(-7) and 10(-6) mol/l concentration MSC had no effect on the NA+ content of a nonpolarized frog bladder tissue preparation, but a 10(-5) nol/l concentration sharply reduced it. The effect of MSC on membrane Na+--K+ ATPase, i.e. on the energy metabolism of cellular tissue, is discussed with reference to these results.

Animals↗
PubMed1976

Muscosal and serosal effects of insulin on ion contents of the frog urinary bladder.

When applied in vitro at the serosal border of the bladder of Rana temporaria insulin (1.7.10(-5) M) brings about a decrease in the tissue sodium content, suggesting a stimulation of the pump extruding sodium ions from epithelial cells. On the other hand, the application of insulin at the two sides of the bladder results in a significant increase of the sodium content of the tissue. It is hence concluded that the contact of the hormone with the mucosal membranes of the epithelial cells of the bladder enhances sodium entry across the membranes. The effect if so pronounced that it obscures the stimulation of the pumps localized at the opposite pole of the cells.

Animals↗
PubMed1976

Absence of a thyroxine effect on the sodium content in the frog urinary bladder.

As a contribution to the discussion whether in vitro thyroxine effects occur at all on anuran epithelial membranes it has been shown that thyroxine 10(-6) and 10(-4) M) produces neither a detectable change in the content of ions and water in the tissue of the urinary bladder of Rana temporaria, nor a change in the oxygen consumption of the bladder or skin of this frog species.

Animals↗