The Localization of Cholinesterases and Non-specific Esterases in the Echinopluteus

The distribution of cholinesterases and non-specific esterases was investigated by means of histochemical methods. The Résults are tentatively discussed in relation to the ontogeny of the larvae, the control of their behaviour, and the evolution of the cholinergic system.     

Omeprazole and ranitidine, antisecretagogues with different modes of action, are equally effective in causing hyperplasia of enterochromaffin-like cells in rat stomach

Female rats were treated for 28 days with high doses of the gastric acid secretion inhibitors omeprazole and ranitidine. Omeprazole, which is long-acting, was given orally once daily. Ranitidine, which is short-acting, was given by continuous infusion (via osmotic minipumps, implanted subcutaneously). The aim was to produce a similar degree of acid inhibition with the two drugs. The inhibition of acid secretion over the day and night was more pronounced in the omeprazole-treated rats (maximal inhibition 100%, minimum 85%) than in those receiving ranitidine (mean 70%). In both groups, there was a great increase in plasma gastrin, somewhat greater after omeprazole than after ranitidine. The gastrin concentration in the antrum was almost doubled by both treatments and there was a moderate increase in the number of antral gastrin cells in the omeprazole-treated rats. The number of enterochromaffin-like (ECL) cells (per visual field) increased in the oxyntic mucosa to the same extent (greater than 100%) in the ranitidine- and omeprazole-treated rats. Apart from the gastrin cells in the antrum and the ECL cells in the corpus no other gastric endocrine cell type seemed to respond to treatments with antisecretagogues. We conclude that, regardless of the type of antisecretagogue used, effective and long-term suppression of gastric acid secretion results in sustained hypergastrinemia and increased number of ECL cells. Conceivably therefore, the ECL cell hyperplasia reflects the trophic effect of gastrin.     

Secretory cells in the foregut of the echinopluteus

Summary Metachromatically-staining substances have been found in the secretion of the stomodeum and esophagus of the echinopluteus (Psammechanus miliaris). This secretion seemed to derive from specialized cells in the wall of the foregut. Ultrastructural examination revealed that these cells are rich in large cisternae containing an electron-translucent material. They are also rich in ribosomes and possess large Golgi complexes. The number of secretory cells increases with age. It is tempting to speculate that the function of these cells is analogous to that of the glandular cells of the endostyle in some chordate phyla.     

Transformation of photoinactive to photoactive protochlorophyllide in isolated prolamellar bodies of wheat (Triticum aestivum) exposed to low pH and ATP

Isolated prolamellar bodies from the etioplasts of dark-grown wheat ( Triticum aestivum L. cv. Walde, Weibull) contain the enzyme NADPH-protochlorophyllide oxidoreductase. The organisation of this enzyme in a pigment-protein complex results in fluorescence emission maxima at 633 and 657 nm. Isolated prolamellar bodies stored in darkness for 24 or 48 h at 4°C (pH 7.2) in the presence of NADPH showed a fluorescence emission ratio 657/633 nm around 4 at −196°C. With acidic conditions this fluorescence ratio increased, with an optimum at pH 5.5. Such an increase was even more pronounced in the presence of ATP and NADPH with ratios up to 8, but was completely blocked when the sulfhydryl inhibitor, dithiobis-nitrobenzoic acid, was added. As shown by sodium dodecyl sulfate polyacrylamide gel electrophoresis the amount of NADPH-protochlorophyllide oxidoreductase in the prolamellar bodies did not change during storage for 24 or 48 h.
The total amount of protochlorophyllide measured in acetone extracts did not change significantly during storage for 48 h. The values were similar for storage at pH 7.2 and 5.5, but at lower pH (around 5) the pigment content decreased to a third.
The most plausible explanation for the increase in fluorescence ratio is that low pH and ATP give rise to a change in conformation, which results in transformation of the short wavelength (633 nm) fluorescing protochlorophyllide to the long wavelength (657 nm) fluorescing form.