Occurrence of lysosomes and the differentiation of rat liver cells

Summary The occurrence of lysosomes has been investigated electron microscopically and cytochemically in cells of rat liver in the course of ontogenesis.It has been found that primary lysosomes occur during the whole period under investigation and that they originate from the Golgi complex. Some of them assume the appearance of multivesicular bodies. Acid phosphatase activity is lower at the prenatal stage than after the birth. The occurrence of secondary lysosomes proceeds in two stages. Secondary lysosomes appear in a high number at the beginning of differentiation of the liver diverticulum (10–12 day of embryonic life). On the subsequent days they are, with few exceptions, no more present. At the end of the embryonic period (starting with the 20th day) and especially after the birth, they progressively grow in number and move from the region of central cytoplasm peripherally towards the bile capillary.Differences in occurrence of secondary lysosomes are in connexion with reconstruction of the liver primordium at the beginning of liver development and with the change in metabolism of the liver cell after the birth.     

A propos des ≪chloride cells≫ dans l'épithélium des lamelles branchiales du poisson rouge

Résumé L'ultrastructure des lamelles branchiales et spécialement celle des chloride cells du poisson rouge (Carassius aureus) a été étudiée. Nous avons constaté que du matériel amorphe floconneux, faiblement adiélectronique était attaché aux endroits des creux apicaux. Afin de préciser la nature de ce matériel, nous avons étudié ces structures au microscope électronique avec les techniques suivantes: acide periodique méthènamine d'argent, colorations au fer colloïdal et au bleu d'alcian. Après la réaction à l'acide periodique méthènamine d'argent, de fines précipitations aux endroits des creux apicaux, correspondant au matériel floconneux visible après la fixation au glutaraldéhyde tétroxyde d'osmium, étaient visibles. La coloration au bleu d'alcian révélait des particules fortement colorées formant un film plus ou moins continu à la surface libre des lamelles, sauf aux endroits oò les chloride cells sont en contact avec la surface. Là et notamment dans les 2reux apicaux, du matériel légèrement granuleux, de faible densité, faisait une couche assez épaisse attachée à la membrane cellulaire. Tenant compte des résultats d'autres auteurs et de nos propres observations, nous considérons que la plus grande partie du matériel se trouvant à la surface des chloride cells, et particulièrement dans les creux apicaux, est de type glycoprotéique.

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The ultrastructure of the chloride cells in the gill epithelium of the goldfish

Summary The ultrastructure of the secondary lamellae of the gills and especially that of the chloride cells of Carassius aureus was studied. We found an amorphous, flakey, slightly adielectronic material in the areas of the apical pits. In order to determine the nature of this material, we studied these structures electronmicroscopically applying the periodic acid silver methenamine, colloidal iron and alcian blue methods. The periodic acid silver methenamine reaction, resulted in finely dispersed precipitations which were deposited in the areas of the apical pits and which correspond to the flakey material seen in the ordinary electron micrographs. The alcian blue method reveales strongly stained particles which form a more or less continuous film on the free surface of the lamellae, interrupted only at the level of the chloride cells. In these areas, notably within the apical pits, a rather thick layer of finely granular low-density material is attached to the plasma membrane. In taking into account other studies performed on this subject, as well as our own observations, we consider the material found on the surface of the chloride cells and particularly within their apical pits to be predominantly of glycoproteinous nature.

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Dédié à Monsieur le Professeur Dr Ernst Horstmann, Hambourg, à l'occasion de son soixantième anniversaire.     

Effect of Antihypertensive Drugs on the “Intrinsic” Heart Rate

“Intrinsic” heart rate in man was measured by giving simultaneous atropine and propranolol and used to study the direct effect of antihypertensive drugs on the heart. Though the intrinsic and control heart rates decreased significantly following the administration of reserpine, there was no significant difference between high and low doses. No similar effects were observed with debrisoquine sulphate and methyldopa, though in high doses the latter produced a decrease which was of some statistical significance.     

Synthesis of 10,11-dihydrofarnesyl pyrophosphate from 6,7-dihydrogeranyl pyrophosphate by prenyltransferase

The syntheses of 6,7-dihydrogeraniol and of its pyrophosphate are described. It is shown that this analogue of geranyl pyrophosphate is a substrate for liver prenyltransferase and that the product synthesized by this enzyme from it and isopentenyl pyrophosphate is 10,11-dihydrofarnesyl pyrophosphate. The K(m) value for 6,7-dihydrogeranyl pyrophosphate was determined to be 1.11+/-0.19mum as compared with 4.34+/-1.71mum for geranyl pyrophosphate. The maximum reaction velocity with the artifical substrate was, however, only about one-fourth of that observed with geranyl pyrophosphate. The binding of isopentenyl pyrophosphate to the enzyme was not affected by the artificial substrate.     

Analogues of geranyl pyrophosphate as inhibitors of prenyltransferase

Six analogues of geranyl pyrophosphate (the monophosphates of geraniol and tetrahydrogeraniol, and the pyrophosphates of nerol, octan-1-ol, tetrahydrogeraniol and citronellol) were synthesized, and were found to be inhibitors of pig liver prenyl- (geranyl-)transferase. The effects of each analogue were analysed in kinetic experiments, which showed the pyrophosphates of citronellol, tetrahydrogeraniol and octan-1-ol to be the most potent inhibitors. The results are interpreted to support a previous hypothesis that the main forces in the binding of substrates to prenyltransferase are non-specific lipophilic forces and a pyrophosphate-binding force.