Comparative effects of caffeine, its analogues and calcium deficiency on cytokinesis

The effects of caffeine, aminophylline, caffeic acid, and calcium deficiency on cytokinesis were studied by light and electron microscopy. All these treatments blocked cell plate formation, resulting in the formation of binucleate cells. The aggregation and organization of membranous vesicles at the ‘presumptive cell plate’ during these treatments appears similar to that of normal cells, but fusion of the vesicles is insufficient to form a complete cell plate. It is suggested that some aspect of membrane recognition and fusion is the process actually interfered with by these treatments. Greater numbers of binucleate cells and fewer partial cell plates were observed in cells treated with caffeine and aminophylline as compared with those exposed to caffeic acid or calcium deficiency, indicating that the latter treatments do not block cell plate formation as efficiently as the former.     

On the locus of action of Na+ at site I of oxidative phosphorylation

The effect of octylguanidine on the Na⁺ stimulated oxygen uptake of rat liver mitochondria and bovine heart submitochondrial particles and on the Na⁺ induced efflux of K from the mitochondria has been examined. The results indicate that the action of Na⁺ is inhibited by octylguanidine, but that the degree of inhibition depends on the concentration of the cation. Apparently, a competition exists between Na⁺ and octylguanidine for a common site. Octylguanidine, but not oligomycin, at certain concentrations restores in mitochondria incubated with Na⁺ the capacity to respond to uncouplers. A competitive effect between monovalent cations and octylguanidine has been observed in submitochondrial particles oxidizing NADH.     

Cholinergic mechanisms in pial vessels

Summary Plexuses of cholinergic nerve terminals were demonstrated (acetylcholinesterase staining) in pial arteries (down to a diameter of about 15) at the base of the brain and on the brain convexities of mice, rats, rabbits, hamsters, guinea-pigs, and cats. The pial veins were less well supplied than the arteries. Consecutive formaldehyde gas treatment (to visualize adrenergic nerves) and acetylcholinesterase staining revealed that the adrenergic and cholinergic plexuses followed each other closely, the axon terminals running together in the same Schwann cell strands. This was confirmed by electron microscopy after KMnO₄ fixation or 5-hydroxydopamine treatment. The varicosities of cholinergic and adrenergic axons were sometimes seen as close as 250 Å. In the neuro-effector area, the terminals of both nerve types (naked or surrounded by an incomplete Schwann cell covering) approached the smooth muscle cells as close as 800–1100 Å, and they were separated from the latter only by the fused neuronal and muscular basement membranes. In this area axo-axonal contacts were observed. The adrenergic, but not the cholinergic, nerves disappeared after bilateral removal of the superior cervical sympathetic ganglia. Isolated cat middle cerebral artery contracted strongly with acetylcholine, and the effect was inhibited by atropine.With regard to the cholinergic neural control of the intracranial arteries, it may have particular functional implications: (1) that these vessels do have a cholinergic parasympathetic innervation in contrast to most other vascular systems, for example, in the mesenterium, (2) that this cholinergic nerve supply was found to be about equally prominent as the adrenergic (sympathetic) innervation which, in some pial vessels, is even better developed than in the mesenteric arteries, and (3) that the adrenergic and cholinergic systems in the intracranial arteries may interact, even at the level of the neuro-muscular contacts, a complex situation which may be partly responsible for the previous difficulties in defining the autonomic neural influence on the brain circulation.Part of the findings were reported at Journées Internationales de Circulation Cérébrale, Toulouse, April 21–22, 1972.     

Fluorescence and electron microscopy of amine-storing enterochromaffin-like cells in tracheal epithelium of mouse

Summary The tracheo-bronchial mucosa of the mouse has been found to contain an extensive system of argyrophilic epithelial cells. In the trachea the cells morphologically resemble enterochromaffin cells. Normally, these enterochromaffin-like cells contain no fluorogenic amine, as revealed by the Falck-Hillarp formaldehyde technique. On the other hand the cells have the capacity to take up and decarboxylate 3,4-dihydroxyphenylalanine (DOPA) or 5-hydroxytryptophan (5-HTP); the amine formed is stored in the cytoplasm in a reserpine-sensitive store. This capacity to produce and store amines under experimental conditions may reflect the presence in the tracheal enterochromaffin-like cells of an amine which can not be demonstrated with available fluorescence histochemical techniques. In the electron microscope the tracheal enterochromaffin-like cells were identified by a positive argyrophil reaction and by their capacity to accumulate radioactivity after administration of ³H-DOPA or ³H-5-HTP as revealed by autoradiography. The radioactive labelling was associated with cytoplasmic electron-dense granules (800–1000 Å), suggesting that the amine formed was stored in these granules. Accordingly, the granules stained argentaffin after DOPA-pre-treatment of the animal. It is suggested that, like similar cells in the gastric mucosa, these argyrophilic enterochromaffin-like cells constitute an endocrine system in which amines are of cytophysiological importance.     

Electron microscopic identification of the histamine-storing argyrophil (enterochromaffin-like) cells in the rat stomach

Summary In the oxyntic gland area of the rat stomach the histamine-containing epithelial cells (also referred to as enterochromaffin-like cells because of their morphologic similarity with the 5-hydroxytryptamine-storing enterochromaffin cells) constitute the system of argyrophil cells in this area as previously shown by the combined use of fluorescence and light microscopic techniques. By performing the argyrophil staining reaction directly on ultra-thin sections it could be demonstrated in the electron microscope that the argyrophil cells have features suggesting that they are endocrine. Based on the ultrastructure of their secretory granules at least two such endocrine cell systems—both argyrophil—could be recognized in the oxyntic glands. The silver deposits were accumulated over the secretory granules of both these cell systems.It is well known that after injection of 1-3,4-dihydroxyphenylalanine, the histamine-storing (enterochromaffin-like) cells of the oxyntic glands store also dopamine. Under these conditions the enterochromaffin-like cells stain argentaffin, which has been shown at the light microscopic level. Also this reaction could be performed directly on ultra-thin sections. By electron microscopy it was then established that the two endocrine cell systems of the oxyntic gland area stained argentaffin upon treatment with 1-3,4-dihydroxyphenylalanine, and that the staining was confined to the secretory granules.The results clearly show that the enterochromaffin-like cells of the rat oxyntic gland area (which is devoid of 5-hydroxytryptamine-containing enterochromaffin cells) are identical with cells characterized as endocrine by ultrastructural criteria, and that gastric non-mast-cell histamine occurs in at least two separate systems of enterochromaffin-like cells.     

Photochemistry and dark equilibrium of retinal isomers and bacteriorhodopsin isomers

European Biophysics Journal -     

Intramodal and interaural specificity of the human slow auditory evoked potential

Parameters of slow auditory evoked potentials (SAEPs) recorded during monotonic monaural stimulation and a programmed change in the frequency of successive tonal stimuli were compared. In one variant of polytonic stimulation, besides the frequency, the side of stimulation also was changed (alternation). During polytonic stimulation the amplitude of the SAEPs was greater than during monotonic. Maximal amplitudes were found during alternating polytonic stimulation. A decrease in the variability of amplitude of the SAEPs and an increase in their peak latencies were observed during polytonic stimulation. It is concluded that SAEPs are characterized by intramodal and interaural specificity. The tonotopic and bilaterally symmetrical organizations of the system of SAEP generation can be demonstrated more satisfactorily at low sound intensities. Data indicating that neuron populations of the system of SAEP generation, perceiving tonal stimuli which differ very little from each other "overlap" to a greater degree than populations perceiving more different sounds, are given, The data on intramodal and interaural specificity of the SAEP are discussed from the standpoint of its extralemniscal origin.State Postgraduate Medical Institute, Tbilisi. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 460–468, September–October, 1977.     

Prostaglandin F2α receptors in bovine corpus luteum cell membranes. Effect of enzymes and protein reagents

Various enzymes and proteins reagents inhibited [³H]prostaglandin F₂α binding to bovine corpus luteum cell membranes. Studies were undertaken (a) to explore further on the dose response relationships with the above agents, (b) to investigate the mechanism of inhibition of binding with respect to receptor affinities and number and (c) to assess whether decreased binding reflected changes in receptors and/or other membrane components.Preincubation of membranes with phoshpolipase A, trypsin, pronase, lipase, tetranitromethane, dinitrofluorobenzene, acetic anhydride and $\text{N-}\text{ethylmaleimide}$ resulted in moderate to drastic inhibitions of [³H]prostaglandin F₂α binding. The dose-dependent inhibition of binding by enzymes, but not by protein reagents (except for $\text{N-}\text{ethylmaleimide}$), exhibited a biphasic pattern: at lower concentrations, the loss of binding was low and relatively plateaued, but at higher concentrations, the losses were dramatic. The drastic reduction in binding by trypsin was due to destruction rather than solubilization of receptors from membranes. Phospholipase A was intrinsically more effective than phospholipases C and Ca²⁺ was not required for its inhibition of [³H]prostaglandin F₂α binding. Protein reagents inhibition of binding was differently influenced by added Ca²⁺ i.e., loss of binding increased with some ($\text{N-}\text{ethylmaleimide}$), decreased with others (tetranitromethane, dinitrofluorobenzene and azobenzene sulfenylbromide). These results are interpreted to indicate that Ca²⁺ induced conformational changes in membranes which may result in exposure of new groups and burying of already exposed modifiable groups.Treatment of membranes wiht trypsin and $\text{N-}\text{ethylmaleimide}$ selectively abolished high affinity prostaglandin F₂α receptors. The low affinity receptors were present but their numbers as well as their affinity were decreased. Lipase, phospholipase A, acetic anhydride, dinitrofluorobenzen and tetranitromethane appear to decrease binding by totally abolishing all prostaglandin F₂α receptors or by severely reducing their affinities.The occupancy of receptors by prostaglandin F₂α afforded considerable protection against trypsin, phospholipase A, lipase and dinitrofluorobenzene. These data indicated that the inhibition of binding by the above agents, at least in part, can be attributable to changes in receptor sites alone.     

A comparative study of metabolite levels in plant leaf material in the dark

Metabolite levels have been compared in the dark and during photosynthesis in leaves and protoplasts from spinach, pea, wheat and barley. In protoplasts the subcellular distribution was also studied. The levels of triose phosphates and sugar bisphosphates were high in the light and low in the dark. The hexose phosphates and 3-phosphoglycerate levels in the dark were very variable depending on the plant material. In most conditions, hexose phosphates and triose phosphates were mainly in the extrachloroplast compartment, while 3-phosphoglycerate and the sugar bisphosphates were mainly in the chloroplast compartment. Leaves always had a very low triose phosphate: 3-phosphoglycerate ratio in the dark, but in protoplasts this ratio was higher. Detailed studies with spinach showed that metabolite levels were very dependent on the availability of carbohydrate in the leaf, particularly starch. Starch mobilisation is not controlled just by the availability of inorganic phosphate and accumulation of phosphorylated intermediates. Hydrolysis of starch may provide precursors for sucrose synthesis while phosphorolysis leads to provision of substrates for respiration. Starch breakdown generates high enough levels of hexose phosphate to support substantial rates of sucrose synthesis in the dark. Respiration is not greatly increased when metabolite levels are high during starch mobilisation. Higher levels of metabolites shorten the length of the induction phase of photosynthesis.Abbreviations Chl chlorophyll - DHAP dihydroxyacetone phosphate - Fru2,6bisP fructose-2,6-bisphosphate - NMR nuclear magnetic resonance - PGA 3-phosphoglyceric acid - Pi inorganic phosphate - RuBP ribulose-1,5-bisphosphate - UDPGlc uridine-5-diphosphate glucose