Transport and control of Ca by pigeon erythrocytes. II. Evidence against a simple feedback control of cell Ca and evidence for the involvement of more than one pool

Cells were subjected to a range of ⁴⁵Ca²⁺ influx loads with A23187. We measured cell ⁴⁵Ca²⁺ with time and A23187 dose, and the apparent ⁴⁵Ca²⁺ influxes (≡“J(in,app)”) at Ca²⁺ steady state. We also measured endogeneous exchangeable and total cell Ca²⁺, which were 50 and 17–220 μM respectively. The effects of A23187 and Ca²⁺ on cell ATP, swelling, net Cl⁻ permeability, and cell morphology were measured. These were modest and do not affect our conclusions.J(in,app) 3 × 10⁻⁴ [A23187]^2.9·[Ca²⁺(o)]μmoles/l·min with 92–552 μM [Ca²⁺(o)] (≡ external Ca²⁺ concentration) and 0–7 μM A23187. J(in,app) was increased an order of magnitude by vanadate and is probably much less than the true influx. The least unlikely explanation found for the high [A23187] exponent, 2.9, was that most of the Ca²⁺ crossing the membrane is expelled by the pump before it can move deeper into the cell.Calcium pumping increased rapidly in response to increased influx, but the steady state cell ⁴⁵Ca²⁺ was approximately proportional to J(in,app) rather than approximately constant between 10 and 120 μmoles/l·min with 184 μM [Ca²⁺(o)]. This is not the result expected from a simple feedback mechanism.At high A23187 doses the pump appears fully activated resulting in a linear relation between cell/medium ⁴⁵Ca²⁺ and [A23187]⁻². From the plot we calculated α≡free/total exchangeable Ca²⁺ = 0.38 ± 0.08 (n = 3) and a maximum pump rate, “Pmax” = 78 μmole/l·min. Pmax is underestimated insofar as J(in,app) is less than the true influx.     

Effects of progestins and antiprogestins on mitochondria in uterine glandular cells in the rat

Summary The administration of progesterone to ovariectomized rats induces an increase in the volume density (Vv) of the mitochondria and the appearance of giant mitochondria in the uterine glandular cells. This experimental model, including a stereological analysis, allowed us to investigate and quantify a direct effect of progesterone on a well-defined cellular structure without the intervention of estrogen in a priming phase. Synthetic compounds, promegestone, gestrinone and RU 38486, were tested in this model either in place of progesterone or simultaneously with progesterone. The potent progestomimetic activity of promegestone was confirmed by the proliferation of giant mitochondria and a high Vv value for the mitochondria, the two other compounds being inactive even at higher doses. At lower doses, gestrinone and RU 38486 partially inhibit the action of progesterone and at higher doses they both show a complete antagonist effect by preventing the development of the mitochondria.     

A method for demonstrating the heterogeneity of pigeon red cell membrane vesicles based on their glycine transport activity

A procedure is described which is capable of detecting the changes in size and/or density of small membrane vesicles resulting from solute uptake. Vesicles which have taken up solute sediment more slowly in a density gradient, the ratio of glycine uptake/vesicle-trapped space is not uniform in the vesicle population, and vesicles with higher uptake/space ratios are preferentially retarded upon centrifugation.Alanine transport activity is associated with glycine transport activity in that retardation of vesicles due to glycine uptake equally retards vesicles possessing alanine uptake activity.     

Contribution to the structural characterization of eucaryotic PSI reaction centre—I. Critical analysis of the polypeptidic composition of different P700 enriched fractions

In thylakoid membranes, several peptides of high MW are present which may interfere with the study of CP1's components. Modifying Cleveland's technique [7] for limited proteolysis, we have characterized the polypeptides found in the 60 kD region. Some may result from incomplete washing of the CF1 while others come from the CP1; indeed, this chlorophyll protein complex, which has a higher MW (above 100 kD), very often undergoes a dissociation into smaller components of about 60 KD MW.Analysis of the protein content of different preparations commonly used to obtain PSI reaction centre enriched fractions has been performed. The and subunits of CF1 are among the main contaminants of most of these preparations. A further purification step is described which can be applied to all these preparations, but numerous peptides are still present in the active fractions. It is most unlikely that all these polypeptides are required for the primary photochemical event, and this emphasizes the necessity to find a new simple method to purify PSI reaction centres.     

Circadian complexes: Circadian rhythms under common gene control

Summary Circadian rhythms for food and water consumption were measured in five inbred strains of mice under a photoperiod of 16 h light and 8 h dark (16:8 LD), and under constant light (LL).Significant strain differences were observed which indicate that a common gene difference, or set of differences inMus musculus influences both the phase angle () associating the rhythms with the light-dark cycle, and the periods (_LL) of circadian rhythms for food and water consumption. The biological clock mechanism influenced by this genetic variance is common to both food and water circadian rhythms, and differs among the five inbred strains. A positive genetic correlation was observed between the phase angle () and the period (_LL) of each rhythm. This observation can be understood in terms of a functional relationship between phase and period proposed by Pittendrigh and Daan (1976b) for the entrainment of a circadian oscillator by a light-dark cycle in nocturnal rodents.These results suggest that circadian rhythms for food and water consumption in mice are regulated by a common physiological mechanism, and would respond to natural selection as a single circadian complex under common gene control.     

Plasma prolactin levels in normal children from birth to adolescence]

Plasma prolactin levels were determined by an homologous radio-immuno assay in normal children: in cord blood, at the first day of life, during childhood and along puberty. 1. In both sexes, there is a very important secretion of prolactin during the neonatal period. 2. Longitudinal studies make obvious a different pattern of plasma prolactin in boys and in girls at puberty.