Diamines interfere with the transport of l-ornithine in Ehrlich-cell plasma-membrane vesicles

1. L-Ornithine transport by plasma-membrane vesicles isolated from Ehrlich cells is Na(+)-independent and shows a saturable and a diffusional component. 2. Putrescine, histamine, 5-hydroxytryptamine and 2,3-diaminopropane at 55 microM concentration significantly inhibit 0.5 mM-L-ornithine transport at least for the first 10 min of incubation. 3. There is a trans-stimulatory effect of putrescine on L-ornithine transport.

Comparison of calcium and magnesium absorption: in vivo and in vitro studies

Transport characteristics of Ca and Mg were compared at three different levels of the absorptive process in male (120-170 g) Wistar rats. Balance studies in intact rats revealed that fractional Ca absorption decreased with increased Ca intake so that net Ca absorption remained constant. Fractional Mg absorption decreased modestly with increased Mg intake so that net Mg absorption increased proportionately with increased dietary Mg. Everted duodenal sacs demonstrated the presence of active Ca absorption with serosal-to-mucosal (S/M) ratio of 2.65 +/- 0.20 (n = 6), which was greater than unity (P less than 0.001). In contrast, the S/M for Mg did not exceed unity. Mucosal duodenal Ca uptake exhibited a large saturable (Michaelis constant of 4.80 +/- 0.34 mM, maximal velocity of 4.71 +/- 0.13 nmol.min-1.mg-1) and a small nonsaturable component (0.12 +/- 0.01 nmol.min-1.mg-1) in 5-wk-old rats (120 g). In 72-wk-old rats (600 g) the diffusional component of Ca uptake became predominant, and the slope increased significantly to 0.32 +/- 0.01 (P less than 0.05). Duodenal Mg uptake was completely concentration dependent and exhibited no age-related changes.

Uptake pathways for amino acids in mouse intestine

This paper characterizes amino acid (AA) uptake pathways in an everted-sleeve preparation of mouse jejunum. AA uptake is linear with time for 2-4 min, depending on the particular AA and its uptake rate. Escape of tracer to the serosal surface is still negligible at these times. Errors due to metabolism of labeled AAs to volatile products can be minimized by using 14C- rather than 3H-labeled AAs and by not drying tissues before counting. The dependence of AA uptake on concentration shows saturable kinetics, with apparent Km values in the range 1-4 mM. By 25 or 50 mM an uptake plateau is reached for leucine, lysine, methionine, and methylaminoisobutyric acid but not for aspartic acid, histidine, or proline. Proline kinetics are the result of a saturable Na+-dependent component, a linear diffusional component, and possibly a small saturable Na+-independent component. The Na+-dependent component of uptake for six AAs averages 83% of the total at 0.01 mM and 54% at 25 or 50 mM. Leucine and D-glucose exhibit modest (32%) cross-inhibition of Na+-dependent uptake. For the same six AAs we determined the percent inhibition of both the Na+-dependent and the Na+-independent components by the other AAs. These results suggest the presence of at least five or six AA uptake pathways in mouse jejunum: distinct Na+-dependent pathways for acidic, basic, and neutral AAs and for imino acids; a shared Na+-independent pathway for basic and neutral AAs; and possibly a Na+-independent pathway for acidic AAs. Comparisons of AA uptake pathways in mouse, rabbit, and rat intestine reveal many similarities but also some differences.

Aerial Gas Exchange in Australian Freshwater/Land Crabs of the Genus Holthuisana

Holthuisana valentula Riek and H. agassizi (Rathbun) both ventilate their lungs by lateral oscillations of the thoracic walls within the branchial chambers. Air enters and leaves the lungs via the prebranchial apertures and the Milne-Edwards apertures. At rest, active ventilation in H. transversa was low (0.95 ml g−1 h−1) and a high diffusional component was evident. After disturbance, VA rose to 45.4ml g−1 and % extraction was low (1.1%). Ventilation increased during moderate hypercapnia and marked hypoxia. MO2 was high after disturbance (2.95μmol g−1 h−1) but declined to very low levels at rest (0.45μmol g−1 h−1). The haemocyanin had a relatively low affinity for oxygen during air-breathing (P50 = 13 Torr) but it was saturated with oxygen at normal PaO2 (56.1 Torr). CCO2 in the haemolymph (13 mmol l−7) was characteristic of air-breathing crabs. The respiratory performances of H. transversa in air and water are compared.