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Biomedical subjects

R Hartmann

Publications and source records attributed to R Hartmann.

At least 145 records · Page 8Linked to original sources
PubMed1978

Potassium uniport and ATP synthesis in Halobacterium halobium.

Light-driven potassium ion uptake in Halobacterium halobium is mediated by bacteriorhodopsin. This uptake is charge-balanced by sodium ions and not by proton release. Light-induced shifts in concentrations of divalent cations were found to be negligible. The transient changes in extracellular pH (alkaline overshoot) can be understood by the concomitant processes of ATP synthesis, proton/sodium exchange and potassium uptake. The driving force of potassium ion uptake is the membrane potential, no ATP-dependent potassium transport process is found. Fluorescence measurements indicate a high permeability of the membrane to potassium ions compared to sodium ions. Therefore the potassium ion diffusion potential contributes to the membrane potential (about 30 mV/decade) and thereby influences the ATP level. Sudden enhancement of the diffusion potential by the potassium ionophore monactin leads to the expected transient increase in cellular ATP level. Due to the large size (up to 100-fold) of the potassium ion gradient and its high capacity (intracellular concentration up to 3 M) the potassium ion gradient can well serve the cell as a long term storage form of energy.

Adenosine Diphosphate↗
PubMed1978

[The effect of glucagon on serum electrolyte concentrations in man].

Intravenous application of 1 mg glucagon causes a significant decrease of the magnesium, calcium, and phosphate concentrations in the serum. Concerning the potassium level there is a biphasic change of concentration. Initially a significant increase of the potassium concentration is to be measured which transgresses into a longer phase of decrease of concentration. The possible causes of these changes of electrolytes after application of glucagon are discussed and it is referred to the possible clinical importance. In longer therapeutic application of glucagon a control of the serum parameters of the electrolytes metabolism appears indicated.

Adult↗
PubMed1977

Bacteriorhodopsin-mediated photophosphorylation in Halobacterium halobium.

The rate of halobacterial photophosphorylation was found to be a linear function of light intensity over a wide range (between 1 and 20 mW/cm2). At higher light intensities (above 25 mW/cm2) the ATP-synthesizing system itself limits the maximal rate of photophosphorylation. The optimal external pH range for this type of photophosphorylation is between pH 6.2 and 7.2 external. The photophosphorylation rate is directly proportional to the bacteriorhodopsin content of the cells. The quantum requirement for photophosphorylation was found to be 22 +/- 5 photons per ATP molecule synthesized. According to Mitchell's chemiosmotic hypothesis of energy coupling phosphorylation can be driven by a membrane potential or a pH gradient or a combination of both. From the results of experiments with drugs which abolish or reduce either one of the two components we conclude that the major driving force for photophosphorylation above an external pH value of 6.5 is the membrane potential, while at more acidic pH value the pH gradient becomes dominating. We did not observe a correlation between a transient alkalinization of the medium and ATP-synthesis upon illumination under certain conditions.

Adenosine Triphosphate↗
PubMed1976

[The effects of lithium ions on circadian rhythms (author's transl)].

Lithium ions lengthen the critical dark period in short-day plants, increase the period length of circadian rhythms in Kalanchoe plants, in the rodent Meriones and influence the activity rhythm of birds. In the case of the Kalanchoe rhythm, mainly the process of the petal opening is affected.

Animals↗
PubMed1975

Separation protest in day-care and home-reared infants.

Separation protest was measured by the onset and duration of fretting or crying in 24 day-care and 28 home-reared infants during a two-minute period of isolated separation from their mothers in an unfamiliar room. Separation episodes were repeated under similarly controlled circumstances at two-month intervals from 3 1/2 through 13 1/2 months and at 20 months of age. The composition of the day-care and home-reared groups was similar for sex, ordinal position, and family background. Day-care and home-reared infants showed similar patterns in the manifestation of separation protest over age, with sharp reductions in latency to crying and marked increases in the occurrence of crying at 9 1/2 and 13 1/2 months. These results suggest that the psychological processes underlying separation protest are not materially altered by the continuing presence of the young infant in a day-care program designed to meet both his physical and psychological requirements.

Age Factors↗