Cholecystokinin-stimulated pepsinogen secretion and cholecystokinin receptors on gastric chief cells in guinea pigs

We investigated cholecystokinin (CCK) receptors on isolated gastric chief cells from guinea pig. CCK stimulated pepsinogen secretion from chief cells at the same efficacy as that induced by carbamylcholine. Binding of 125I-labeled CCK-33 (125I-CCK) to chief cells was temperature-dependent, and was saturable and reversible at 37 degrees C. Hofstee plots of the ability of CCK-8 to inhibit binding of 125I-CCK showed a linear regression line, suggesting that CCK receptors possessed one binding site. The dissociation constant of the binding site was calculated to be 3.8 x 10(-10) M. The dose-response curve of CCK for pepsinogen secretion was superimposed on that for the binding to its receptors. These results indicated that gastric chief cells from the guinea pig possess CCK receptors that relate closely to the action of CCK involved in pepsinogen secretion.     

Homoeosis in Drosophila: The Lethal Syndrome of the Regulator of bithorax (or trithorax) Locus and Its Interaction with Other Homoeotic Loci

Regulator of bithorax (Rg-bx)^- [or trithorax (trx)^-] lethal zygotes show anterior transformations of various cuticular features of the larval thorax and abdomen. The Rg-bx^- lethal syndrome depends on the dosage of the bithorax gene complex (BX-C), and lack of Rg-bx⁺ function is antagonistic to posterior transformations displayed by Polycomb ( Pc)^- embryos. Significantly, when the BX-C is deleted, the Rg-bx^- embryos disclose homoeosis of mesothoracic to prothoracic cuticular structures. This homoeotic transformation is due to a reduction in Antennapedia (Antp)⁺ gene activity and is consequently dependent on the dosage of the Antennapedia gene complex (ANT-C), suggesting that the Rg-bx⁺ activity is necessary for proper expression of the Antp⁺ gene. However, the functional relationship between the Rg-bx and Sex combs reduced (Scr) loci in embryogenesis is still to be established.     

Nucleic acid binding and mutagenicity of active metabolites of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline

2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) is a potent mutagen and carcinogen present in heated foodstuffs. The covalent binding of MeIQx to calf thymus DNA and calf liver RNA with microsomal activation was demonstrated. A major metabolite which exerts a direct mutagenic effect on S. typhimurium TA98 was found by HPLC analysis after incubation of MeIQx with rat liver microsomal fraction. The metabolite was identified as 2-hydroxyamino-3,8-dimethylimidazo[4,5-f]quinoxaline (N-OH-MeIQx). Synthetic N-OH-MeIQx was found to bind non-enzymatically to DNA and RNA at neutral pH even at 0 degrees C. Addition of acetic anhydride increased the binding of N-OH-MeIQx to DNA 10 times. These results suggest that MeIQx is metabolized to N-OH-MeIQx by microsomal cytochrome P-450 and further activated to an acetylated form that binds efficiently to nucleic acids in rat liver. Preferential modification of polyguanylic acid suggests that guanine residues of DNA are mainly modified with MeIQx. Synthetic N-OH-MeIQx exerted direct mutagenic activity on S. typhimurium TA98 inducing 150,000 rev/micrograms. Pentachlorophenol (PCP) caused a dose-dependent inhibition of this mutagenic effect, but 2,6-dichloro-4-nitrophenol (DCNP) did not. Thus the acetyltransferase of S. typhimurium seems to be important for the high mutagenicity of MeIQx after its microsomal activation.     

Photosynthetic Characteristics of Photoautotrophically Cultured Cells of Tobacco

The photosynthetic characteristics of photoautotrophically culturedcells of tobacco (Nicotiana tabacum cv. Samsun NN) as well asthose of photomixotrophically cultured cells and green leaveswere investigated. Analyses revealed that on a fresh weightbasis cultured tobacco cells had lower chlorophyll contentsthan cells of green leaves. The chlorophyll content per chloro-plast,however, was almost the same in both types of cell, and thechloroplast number per cell accounted for only small differencesin the cellular chlorophyll content. This indicates that thelarger cell volume of cultured cells is the main factor in thedifference in the chlorophyll content of these cells. Photosynthetic activity measurements also showed differencesin the chloroplasts of cultured and leaf cells. The maximumactivities of photosystem I and the Hill reaction for the culturedcells were about half those for leaf cells on a per unit chlorophyllbasis. Moreover, photo-autotrophic cells had relatively constantphotosystem I and Hill reaction activities during growth; whereas,on a fresh weight basis these activities in leaf cells reflecteddevelopmental changes in the chlorophyll content. Lithium dodecyl sulfate-polyacrylamide gel electrophoresis showedqualitatively similar thylakoid polypeptide compositions forcultured and leaf cells at all stages of growth even thoughthere were quantitative decreases in the contents of severalpolypeptides in the cultured green cells (especially in photomixotrophiccells) in comparison to the polypeptide contents of tobaccoleaves. We speculate that the lower photosynthetic activityof the cultured cells may be caused by this reduction in thecontents of certain thylakoid polypeptides. (Received November 14, 1988; Accepted June 19, 1989)     

Effects of antibody to 5 S-RNA-binding protein on protein synthesis in Artemia salina ribosomes.

The effects of an affinity-purified polyclonal antibody to Artemia salina ribosomal protein L5 on protein synthesis in vitro were examined. The antibody interacted with 60 S subunits more strongly than with 80 S ribosomes, and inhibited reassociation of ribosomal subunits to some extent at 5 mM-Mg2+ but not at 10 mM. Polyphenylalanine synthesis in vitro at 10 mM-Mg2+ was significantly inhibited, especially when the antibody was first preincubated with 60 S subunits prior to the assay. The incorporation of amino acid directed by globin mRNA was inhibited only when the preincubation with 60 S subunits was carried out. On the other hand, no effect was detected on elongation factor 2- and 60 S subunit-dependent uncoupled GTPase activity. These results suggest that L5 is probably located at or near the subunit interface and may play an important role in protein synthesis.     

Centrifugal decrement in diameter of myelinated afferent fibres innervating frog taste organ

1. Regional changes in the diameter of single myelinated afferent nerve fibres innervating the taste disc of the fungiform papillae on the bullfrog tongue were investigated morphologically and functionally. 2. The diameter of myelinated afferents in the medial lingual branch of the glossopharyngeal nerve averaged 8.4 microns at the proximal end of the tongue and gradually decreased at the rate of 0.8 micron/cm length of the fibres as they ran in the apical direction of the tongue. 3. The conduction velocity of single myelinated afferent fibres within the tongue decreased gradually as they ran peripherally. 4. Electrophysiological inspection of neural connections between the fungiform papillae suggests that a gradual centrifugal decrease in the diameter of a single myelinated afferent fibre is not due to multiple bifurcations of the fibre at various sites within the tongue, but due to a natural gradual decrease in the thickness of the myelin sheath and the diameter of axon.     

Effect of disuse on the ultrastructure of the achilles tendon in rats

We examined the influence exerted, through disuse of the hindlimb, on the collagen fibres of the achilles tendon in rats. With disuse the body mass decreased by 28%, and the mass of soleus muscle decreased by 20%. A decrease in the surface area and diameter was observed in the experimental group when compared to the control group. A histogram of the collagen fibres showed a decrease of the thick fibres in the experimental group. The maximum surface area of collagen fibres in the experimental group was seen to be only 43% of that of the control group. These results showed a decrease in the thickness of the collagen fibres of the achilles tendon through disuse. This seemed to suggest that resistance to tension is decreased by disuse.     

Catecholaminergic innervation of GRF-containing neurons in the rat hypothalamus revealed by electron-microscopic cytochemistry

Summary The Catecholaminergic innervation of neurons containing growth hormone-releasing factor (GRF) was examined by use of a method which combined either 5-hydroxydopamine (5-OHDA) uptake or autoradiography after intraventricular injection of ³H-noradrenaline with immunocytochemistry for GRF in the same tissue sections at the electron-microscopic level. In the ventrolateral part of the arcuate nucleus of the rat hypothalamus a large number of immunonegative axon terminals were found to make synaptic contact with GRF-like immunoreactive (GRF-LI) cell bodies and processes. ³H-noradrenaline autoradiography or 5-OHDA-labeling combined with GRF immunocytochemistry revealed that axon terminals labeled with ³H-noradrenaline or 5-OHDA make synaptic contact with the GRF-LI nerve cell bodies and processes. These findings indicate that catecholamine-containing neurons innervate GRF neurons to regulate GRF secretion via synapses in the rat arcuate nucleus.     

Possible relationship between poly(ADP-ribose)synthetase and formation of antibody against acetylcholine receptors in patients with myasthenia gravis

We examined the relationship of the serum levels of antibody against acetylcholine receptors to the serum levels of 13 enzymes, including various hydrolytic enzymes, poly(ADP-ribose)synthetase (Poly(ADP-ribose)Syn), and sialyltransferase (NANA-trans), in patients with myasthenia gravis. The patients were divided into two groups, depending on the presence or absence of thymoma. In spite of the absence of significant difference in the absolute levels of individual enzymatic activities between the two groups, the network relationships of such enzymes were quite different between the two groups. Of the 13 enzymes examined, only Poly(ADP-ribose)Syn showed a weak but significant correlation with the level of the antibody in the patients without thymoma. A multivariate study more clearly suggested the relationship between the antibody formation and Poly(ADP-ribose)Syn in the patients without thymoma. Such observations were not found in the patients with thymoma.