Bulk properties of the lipid bilayer are not essential for the thermal stability of Na,K-ATPase from shark rectal gland or pig kidney

The thermal stability of Na,K-ATPase from pig kidney is markedly greater than that of Na,K-ATPase from shark salt glands. The role of the lipid bilayer is studied by solubilisation of the membrane-bound enzyme in the nonionic detergent octaethyleneglycoldodecylmonoether (C₁₂E₈), addition of excess dioleylphosphatidylcholine (DOPC) or palmitoyloleylphosphatidylcholine (POPC) and reconstitution of membranes by removal of detergent. At 54 °C the reconstituted enzymatically active pig enzyme retains a high thermal stability, and reconstituted shark enzyme retains a low thermal stability, even with a 9-fold excess of DOPC. This result suggests that the origin of the difference in thermal stability is not related to bulk lipid properties of the native membranes.     

Interactions Between the Nematode Parasite of Pigs,Ascaris suum,and the Earthworm Aporrectodea longa

Pig faeces in which Ascaris suum eggs had been embryonating for 57 days were placed in buckets of soil containing either 30 or no earthworms (Aporrectodea longa). When present, earthworms consumed the faeces and transported the eggs down into the soil, without inflicting any visible damage on the eggs. In later experiments 10 earthworms from the above experiment were fed to each of ten pigs, and another 40 earthworms were dissected. None of the 10 pigs became infected with A. suum through consumption of earthworms, and none of the dissected earthworms were found to contain A. suum larvae. This experiment indicates that A. longa did not act as a paratenic host for A. suum but shows that earthworms are very efficient in transporting A. suum eggs from faeces deposited on the soil surface into the soil.     

Endothelium-dependent responses in small human mesenteric arteries

The aim of the present study was to investigate the endothelial function in human mesenteric arteries with specific reference to defining the role of endothelium-derived nitric oxide (EDNO) and the endothelium-derived hyperpolarizing factor (EDHF). Isolated segments of small human mesenteric arteries (225-450 microm inner diameter) were mounted in organ baths for recording isometric tension. In arteries precontracted with U46619 (thromboxane A(2) analogue, 10(-7) M), endothelium-dependent relaxations were induced in a concentration-dependent manner by substance P and histamine. In normal Krebs solution the relaxations to substance P (10(-9) M) and histamine (10(-7) M) were not significantly affected by preincubation with N(omega)-nitro-L-arginine (L-NNA, 10(-4) M) or indomethacin (10(-5) M). When the preparations were exposed to a solution containing 60 mM KCl, stable contractions were induced, but relaxations could still be induced by substance P and histamine. When the arteries were further preincubated with L-NNA, the relaxations were almost abolished. A combination of apamin (3 x 10(-7) M) and charybdotoxin (10(-9) M) almost abolished relaxations in normal Krebs solution. It is concluded that isolated human mesenteric arteries respond to substance P and histamine with relaxations that are endothelium-dependent. Synthesis of both EDNO and EDHF seem important for these relaxations, whereas prostaglandins seem to be of minor importance.