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At least 235 records · Page 13Linked to original sources
PubMed1991

[The role of hyperpolarization and depolarization of the membrane of the human spermatozoon].

The electric potential across the membrane (psi) is evaluated through the accumulation of the lipophilic, radiolabelled, triphenylmethylphosphonium (3H-TPMP+), cation on membrane human sperm. The washed sperm cells, were incubated in presence of 3H-TPMP+ in low-K+ medium or high-K+ and allowed to take up the cation to steady-state (ie; 20 min at 37 degrees C). By using this differential, the value obtained was inserted in the Nernst equation, this value yielded a psi of -69 +/- 2 mV. The presence of divalent cations Zn++ and Mg++ in the incubation medium both induced a hyperpolarization of 10% and 8.6%, respectively. The addition of specific reagents such as p-chloromercuribenzene-sulfonate and ethylene-diamine-tetraacetic acid sodium salt both decreased the psi 35% and 58% respectively. The agents to act upon the components of the sperm cell membrane such as the dithiothreitol and progesterone induced hyperpolarization and depolarization of the membrane 16% and 40%, respectively. The presence of propranolol and L-alpha-lysophosphatidylcholine, which affect the ionic gradients present across the plasma membrane, both induced a depolarization from 43% and 92% respectively. Finally, the addition of tetraphenylboron (TPB-) on the incubation medium, enhanced the value of the psi 75%. These studies are transcendent because with the utilization of agents depolarizing, or hyperpolarizing we obtain changes in the psi from -80 +/- 0.6 mV, until -6 +/- 0.6 mV changes of 74 +/- 1.5 mV across of the sperm cell membrane.

Cell Membrane↗
PubMed1990

[Nutritive physiology of Psoralea corylifolia L].

Our study has shown that P. corylifolia absorbs and accumulates N2 and K2O most speedily in the periods of branching, flowering and fruiting, while P2O5 in the period of full flowering and fruiting. P2O5 is accumulated mainly in the seed and K2O in the stem. The nutriment accumulation is positively correlated with that of dry substances. To produce 100 kg of P. corylifolia an absorption of 10.59 kg of N2, 3.68 kg of P2O5 and 10.21 kg of K2O is needed.

Fabaceae↗
PubMed1990

Radiopharmaceutical factors in the variable quality of [99mTc]HM-PAO images of the brain.

Variability in the quality of [99mTc]HM-PAO images of the brain has been attributed to differences between kits and the addition of excessive amounts of pertechnetate to the kits. A retrospective study showed no significant differences between batches of kits with respect to radiochemical purity (RCP) or image quality. Up to 3000 MBq (81 mCi) pertechnetate could be added to the kit without adversely affecting RCP or image quality. It was shown that image quality was directly affected by RCP at time of injection and dropped sharply when RCP fell below 85%. Interstitial injection and mixing with blood prior to injection also resulted in poor image quality. Pretreatment with perchlorate reduced uptake of activity in the parotid glands; this improved image quality and reduced the influence of RCP.

Brain↗
PubMedDate not supplied

A carbon-limited medium for growth and sporulation of Bacillus thuringiensis var. kurstaki.

A culture medium for batch production of d-endotoxin by Bacillus thuringiensis (B., t.) has been modified. Through batch and continuous cultivation studies, the original medium was diagnosed to be limited in organic nitrogen. Corn steep liquor was found to be an excellent source for the organic nitrogen and its addition resulted in a carbon limited medium and in a significant increase in the amount of spore-toxin complex formed in shake flasks. Results of bioassay, conducted on Trichoplusia ni, suggest enhancement of larvicidal efficacy under carbon-limited growth conditions.

Ammonium Sulfate↗
PubMed1991

Citrate and renal calculi: new insights and future directions.

Citrate is pathogenetically important in stone formation, because it retards the crystallization of stone-forming calcium salts and because its level in urine is low in many patients with nephrolithiasis. Potassium citrate is useful therapeutically, because it can often restore normal urinary citrate. Hypocitraturia often results from dietary aberrations, including sodium excess, and exaggerated intake of animal proteins. Hypocitraturia is frequently accompanied by a low net gastrointestinal absorption of alkali. New drugs are under development as improvements or refinements of currently available potassium citrate. They are potassium citrate 10-mEq-tablet preparation, effervescent calcium citrate, and potassium-magnesium citrate.

Animals↗
PubMed1950

Accumulation of potassium by human red cells.

1. A method is described for measuring the accumulation of K at 37 degrees C. by washed human red cells in glucose-containing systems in which the pH is kept constant, the K content of the cells being compared with that of the cells of systems which contain no added glucose but which are otherwise treated similarly. 2. In systems containing added glucose, the accumulation of K begins shortly after the cells have been warmed to 37 degrees C., proceeds to a maximum which is reached after about 10 hours, and then falls exponentially. The maximum rate of accumulation is found during the first 3 hours. In systems which contain no added glucose, the K content of the cells appears to decrease exponentially with time for about 18 to 24 hours; thereafter the K content of the cells may decrease rapidly and the systems may show considerable hemolysis. Sometimes a small accumulation effect is observed during the first 2 to 3 hours; this may be the result of the washed cells not having been completely freed of glucose. 3. The accumulation process proceeds at its maximum rate at pH 7.4 to 7.6, which is also the pH at which the K loss from the red cells is at a minimum in systems containing no added glucose. 4. When red cells are stored at 4 degrees C. for increasing lengths of time, the storage is accompanied by increasing K loss and the maximum rate of accumulation observed when the cells are warmed to 37 degrees C. at first becomes greater. If the storage at 4 degrees C. is continued for more than 3 to 4 days, the rate of the accumulation which occurs at 37 degrees C decreases again, the accumulation mechanism showing progressive deterioration with time even at low temperatures. This deterioration has a counterpart in the progressive deterioration (deduced from the analysis of the curves relating K content and time) of the accumulation mechanism with time at 37 degrees C. 5. The accumulation of K occurs at a maximum rate when the concentration of glucose in the system is between 50 and 200 mg./100 ml. Its temperature coefficient over the range 27-37 degrees C. is 2.4. In the presence of glucose and at pH 7.6, accumulation of K takes place from isotonic mixtures of KCl and LiCl or of KCl and CsCl only a little less actively than from mixtures of KCl and NaCl; i.e., the accumulation of K under optimum conditions seems to be an active process which is at least partly independent of the excretion of Na.

Biological Transport↗