Biomedical subjects

K Turnheim

Publications and source records attributed to K Turnheim.

At least 73 records · Page 4Linked to original sources

PubMed1977

Secretion of monoquaternary ammonium compounds by guinea pig small intestine in vivo.

In anesthetized guinea pigs N-(3H)methylscopolamine (NMScop), N1-(14C)methylnicotinamide (NMN), and (14C)tetraethylammonium (TEA), administered intravenously, were secreted against a concentration gradient into the lumen of the small intestine. The concentration ratio of unmetabolized ammonium base in the intestinal lumen to that in the plasma was 4.3 and 6.5 for NMScop and NMN, respectively, 75 min after the intravenous injection of 1 nmole/g body weight of the individual compounds. The corresponding value for TEA after 180 min was 2.0. The establishment of the concentration gradient between intestinal lumen and plasma was diminished with increasing doses. An excess of NMN inhibited the uphill transport of NMScop. Since the electrical potential difference across the intestinal epithelium and a 'fluid circuit' mechanism cannot solely account for the observed accumulation of the monoquaternary ammonium compounds in the intestinal lumen, the evidence presented supports previous in vitro findings that the small intestine is capable of actively secreting organic cations.

Animals↗

PubMed1977

Weak electrolyte transfer in the guinea pig jejunum: secretion of trimethoxybenzoic acid.

In isolated epithelia of guinea pig jejunum the transcellular permeation of 10(-4) M (carboxyl-14C)-3,4,5-trimethoxybenzoic acid (TMBA) in the direction blood-lumen was more than 10 times greater the transcellular permeation of 10(-4) M (carboxyl-was reduced to less than 2 by anaerobiosis or by increasing TMBA concentrations of up to 10(-2) M. Under aerobic conditions the cellular uptake of TMBA (10(-4) M) from the blood side was twice as high as that from the lumen side. In anaerobiosis the percentage of TMBA taken up into the epithelium was enhanced, when TMBA was administered on the lumen side, while the percentage was unchanged after administration on the blood side; thereby the difference in cellular TMBA concentrations was abolished. Similar results were obtained under aerobic conditions, if the TMBA concentration was increased up to 10(-2) M. The results are consistent with a three-compartment model with an intermediate compartment distinguished by a high pH as compared to that of the outer compartments and by a luminal boundary highly permeable for the ionized form of the substrate in contrast to the contraluminal boundary.

Aerobiosis↗

PubMed1977

Adenosine uptake by the isolated epithelium of guine pig jejunum.

The uptake of [8-14C]adenosine by the isolated epithelium of guinea pig jejunum was faster than that of inosine, hypoxanthine, or adenine. The initial velocity of adenosine uptake from both the luminal and the antiluminal side of the epithelium exhibited saturation kinetics. The apparent Km, V, and passive permeability of luminal adenosine uptake were all lower than the corresponding values of antiluminal uptake. p-Nitrobenzyl-thioguanosine inhibited adenosine uptake from both the luminal and the antiluminal side, whilst hexobendine decreased the uptake only from the antiluminal side of the epithelium. The results suggest that adenosine enters the intestinal epithelium by a carrier-mediated process in addition to passive diffusion. The antiluminal transport system for adenosine seems similar to that of other tissues with respect to hexobendine inhibition; the luminal transport mechanism, however, exhibits different properties, being insensitive to hexobendine.

Adenine↗

PubMed1977

Salvage of adenosine, inosine, hypoxanthine, and adenisine by the isolated epithelium of guinea pig jejunum.

The metabolism of adenosine, inosine, hypoxanthine, and adenine (labelled with 14C in the carbon 8 position) at a concentration of 5 X 10(-6) M was studied in isolated epithelium of guinea pig jejunum. When adenosine or adenine was added to the antiluminal side of the epithelium, two-thirds or one-half, respectively, of cellular radioactivity was incorporated into the nucleotide fraction, mainly in the form of adenine nucleotides. Nucleotides synthesis from inosine or hypoxanthine was significantly smaller than that from adenosine. By contrast, another metabolic patern was found after luminal administration of adenosine, inosine, or hypoxanthine: the incorporation rate into the nucleotide fraction was equally high and the label was recovered in IMP and adenine nucleotides to about the same extent with all three substrates. Purine riboside (10(-4) M) significantly depressed nucleotide formation from adenosine, with respect to IMP formation in particular, while no change was observed in inosine or hypoxanthine salvage. The results suggest compartmentation of the enzymes of purine metabolism within the intestinal mucosa. The significance of this conclusion with regard to the salvage pathway is discussed.

Adenine↗

PubMed1976

Limitations of the direct linear plot in evaluation of drug-protein binding parameters.

The applicability of the direct linear plot is compared with that of the Scatchard plot for the estimation of protein binding parameters. Only, if one class of binding sites exists in the system tested, binding parameters may be estimated by use of the direct linear plot. On the other hand the Scatchard plot also provides estimates in systems with more that one class of binding sites.

Binding Sites↗

PubMed1976

Myocardial glucose uptake and breakdown during adenosine-induced vasodilation.

In isolated K+ (16.2 mM)-arrested cat hearts perfused at constant pressure adenosine infusions (0.8 mumoles - min-1 - 100 g-1 for 10 min) caused an increase in myocardial 14C-glucose uptake and release of 14CO2 + H14CO3- AND 14C-lactate simultaneously with a rise in coronary flow. The ratio of the release of 14CO2 + H14CO3- to that of 14C-lactate and the specific activity of lactate in the effuate were not altered. In K+ -arrested hearts perfused with constant volume neither glucose uptake nor glucose breakdown were influenced by 0.8 or 100 mumoles - min-1 - 100 g-1 adenosine with 0.1 - 5 mM glucose in the perfusion medium. It is concluded that adenosine does not affect directly the myocardial glucose carrier system, aerobic or anaerobic glucose breakdown or glycogenolysis, but enhances glucose uptake secondarily by increasing coronary flow. This interpretation is substantiated by the finding that mechanically produced increases in perfusion volume caused similar increases in myocardial glucose uptake as were observed with comparable adenosine-induced coronary flow increments.

Adenosine↗

PubMed1975