The stimulating and inhibitory effect of carbamoylcholine on decamethonium uptake by slices of mouse kidney

The present study was performed to decide whether a common mechanism is involved in the accumulation by mouse kidney slices of the quaternary ammonium compounds decamethonium and carbamoylcholine. Slices were incubated (1 hr) in Krebs-Ringer bicarbonate medium (37°, pH 7.4) containing [¹⁴C]decamethonium (2 × 10⁻⁶M) in presence or absence of carbamoylcholine. The decamethonium uptake was significantly increased by 10⁻⁴M-3 × 10⁻³M carbamoylcholine, whereas 2 × 10⁻²M and 3 × 10⁻²M carbamoylcholine significantly inhibited the uptake. Initial decamethonium uptake (3 min incubation) was significantly stimulated when slices were preincubated (1 hr) with 3 × 10⁻³M carbamoylcholine before transfer to a carbamoylcholine-free medium containing decamethonium. This suggests a relationship between the stimulating effect and the presence of carbamoylcholine in the slices. No efflux of decamethonium (incubation period 15 min) occurred from slices preincubated (1 hr) with decamethonium (2 × 10⁻⁶M), which means that stimulation cannot be attributed to inhibition of decamethonium efflux by carbamoylcholine. The above results support the assumption that decamethonium and carbamoylcholine share a common transport mechanism. The stimulation phenomenon can be interpreted as an example of accelerative exchange diffusion, which should mean that carbamoylcholine efflux accelerates decamethonium influx.     

Cisplatin-induced injury to calcium uptake by mitochondria in glutathione-depleted slices of rat kidney cortex

Changes in functional activities of mitochondria from kidney cortical slices incubated with cisplatin and the glutathione depletor diethylmaleate were examined. Diethylmaleate, which decreased the glutathione level in the slices, enhanced the cisplatin-induced decreases in glutathione level and calcium uptake in the mitochondria. The movement of cisplatin into mitochondria in the slices was not affected by diethylmaleate. These results suggest that the depressions in glutathione level and calcium uptake by cisplatin in mitochondria are enhanced by a decrease in cytoplasmic glutathione.     

Absorption and secretion of monoquaternary ammonium compounds by the isolated intestinal mucosa

The transepithelial permeation and the cellular uptake of N-methylscopolamine (NMScop), N¹-methylnicotinamide (NMN), and tetraethylammonium (TEA) were studied in the isolated jejunal mucosa of the guinea pig. (1). The permeation rate, corrected for the fraction passing through the mucosa via an extracellular route (corr. permeation), was significantly higher in the direction blood-to-lumen than in the direction lumen-to-blood with concentrations below 500 μM. The corr. permeations' ratio at concentrations of 0.1 and 1 μM NMScop was 12, the corresponding values for 1 μM NMN and 50 μM TEA were 2.5 and 2, respectively. The corr. permeation blood-to-lumen decreased with increasing concentrations administered, and with the highest concentrations (1000–2000 μM) the differences in permeation in the two directions were insignificant. During anaerobiosis the corr. permeation ratios approached 1 with all concentrations, and the corr. permeations were not dependent on the concentrations administered. (2). The kinetics of cellular uptake displayed similar characteristics: the uptake from the blood side was significantly larger than that from the lumen side of the mucosa. This difference decreased with increasing concentrations or anaerobiosis without being abolished completely. (3). The three monoquaternary ammonium compounds were transported uphill, creating a concentration ratio lumen-side/blood-side greater than 1, which was highest with NMScop (1.65 within 180 min). The establishment of this gradient was prevented by anaerobiosis. (4). Rising concentrations of NMScop progressively inhibited the corr. permeation from blood to lumen and the cellular uptake of NMN from the blood side of the mucosa. The results demonstrate the existence of an active secretory system for monoquaternary ammonium compounds in the jejunal epithelium. The experimental data are consistent with a cell model, which has two transport systems in series, one in the basal and one in the luminal cell membrane and both directed towards the intestinal lumen, plus a non-saturable pathway in each of the two cell membranes.     

The influence of drugs on the uptake of acetylcholine by slices of rat cerebral cortex

1. The acetylcholine content of cortical slices from rat brain, was determined after incubation for 30 min in a medium containing acetylcholine (4 mug/ml.). The cholinesterase activity of the slices had been inhibited by pretreatment with 3,3-dimethyl-n-butyl 2-methylphosphonofluoridate (soman).2. Acetylcholine accumulated in the tissue slices, up to a concentration of about six times that in the medium.3. The uptake of acetylcholine was partly inhibited by potassium in high concentrations.4. Hemicholinium-3, O-ethyl S-diethylaminoethyl ethylphosphonothiolate, physostigmine, atropine and choline, in that order of potency, inhibited the accumulation of acetylcholine in the cortical slices, but soman and ethyl N,N-dimethyl phosphonoamidocyanate (tabun) had no effect on the uptake of acetylcholine.5. Substances interfering with energy metabolism, such as 2,4-dinitrophenol, oligomycin, sodium azide, amylobarbitone sodium and p-chloromercuribenzoate inhibited the uptake of acetylcholine. Ouabain had little inhibitory effect.6. In anaerobic conditions the accumulation of acetylcholine in the tissue slices was nearly blocked.7. The uptake of acetylcholine in the tissue slices was dependent on temperature. The Q(10) was about 2.8. Autoradiography of sections from slices in which (3)H-acetylcholine had accumulated showed a diffuse distribution of radioactivity in the cytoplasm of all cells. There was no visible preference for certain cells or cell structures.     

The uptake and metabolism of 3H-catecholamines in rat cerebral cortex slices

Summary The accumulation and metabolism of ³H-catecholamines were studied in cerebral cortex slices obtained from rats pretreated with reserpine, during 30 min of incubation with 50 nmol/l of the ³H-amines. In some experiments neuronal uptake (uptake,) was inhibited by the presence of 0.3 mol/l desipramine, in others COMT was inhibited by 30 mol/l U-0521. When both MAO and COMT were intact, most of the metabolism of ³H-noradrenaline was neuronal (i. e., desipramine-sensitive). For ³H-adrenaline rates of neuronal metabolism were much lower than for ³H-noradrenaline, non-neuronal O-methylation accounting for about 50% of total metabolism. Rates of metabolism of ³H-dopamine were similar to those of ³H-noradrenaline, but with a predominance of non-neuronal metabolism, which involved O-methylation and deamination. Under these conditions, very little ³H-catecholamine was recovered from the tissues; moreover, desipramine tended to increase tissue levels. Hence, tissue content then appears to partly reflect extracellularly distributed ³H-amines. After block of MAO rates of metabolism of ³H-noradrenaline and ³H-dopamine were greatly reduced, and tissue levels were increased. Desipramine now antagonized the accumulation of ³H-amines in the tissue, while U-0521 increased it. Rates of O-methylation (in the presence of desipramine) increased in the order ³H-noradrenaline < ³H-dopamine. It is concluded that neuronal uptake is associated with MAO only, and rates of neuronal deamination increased in the order: ³H-adrenaline < ³H-dopamine « ³H-noradrenaline. Non-neuronal uptake is associated with both, COMT and MAO, and rates of non-neuronal metabolism increased in the order: ³H-adrenaline < ³H-noradrenaline « ³H-dopamine.Abbreviations COMT catechol-O-methyl transferase - DOMA dihydroxymandelic acid - DOPAC dihydroxyphenylacetic acid - DOPEG dihydroxyphenylglycol - DOPET dihydroxyphenylethanol - HVA homovanillic acid - MAO monoamine oxidase - MN metanephrine - MOPEG methoxyhydroxyphenylglycol - MOPET methoxyhydroxyphenylethanol - NMN normetanephrine - 3-OMT 3-O-methyl-tyramine - VMA vanillylmandelic acid Supported by the Deutsche Forschungsgemeinschaft (SFB 176) Send offprint requests to U. Trendelenburg at the above addresswith the technical assistance of M. Babl     

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

Summary In anaesthetized 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.Parts of this paper were presented at the 13 th Spring Meeting of the German Pharmacological Society, Mainz, 1972 [Naunyn-Schmiedeberg's Arch. Pharmacol. 274, R118 (1972)]     

The action of indoramin and other compounds on the uptake of neurotransmitters into rat cortical slices

Indoramin has been tested for its ability to inhibit the uptake of tritiated (-)-noradrenaline and 5-hydroxytryptamine into rat brain cortical slices. Other alpha-blocking agents and tricycic antidepressants were included for comparison. Activity against noradrenaline uptake is probably not important in the therapeutic action of indoramin. However, inhibition of 5-hydroxytryptamine uptake may be responsible for the sedation in high dosage noted by some investigators,     

The effect of chlorpromazine on the uptake and efflux of paraquat in rat lung slices

The uptake of paraquat by rat lung slices was inhibited by chlorpromazine in a concentration- and time-dependent manner. In addition, the efflux of paraquat from lung slices was enhanced by chlorpromazine in a similar fashion. These in vitro findings suggested that chlorpromazine might be useful in vivo in reducing pulmonary paraquat content and, in turn, its pneumotoxicity. However, chlorpromazine potentiated the lethal toxicity of paraquat rather than ameliorating it. This potentiation by chlorpromazine was found to correlate with a reduction in the urinary excretion of paraquat and concomitant increase in pulmonary paraquat concentrations.