Intracellular transport of endocytosed chylomicron [3H]retinyl ester in rat liver parenchymal cells. Evidence for translocation of a [3H]retinoid from endosomes to endoplasmic reticulum

The intracellular transport of chylomicron remnants labeled with [3H]retinyl ester was studied in rat liver parenchymal cells by means of subcellular fractionation in Nycodenz and sucrose density gradients. The data presented indicate that endocytosed chylomicron remnant [3H]retinyl ester initially is located in low density endosomes. Radioactivity is subsequently transferred to a denser vesicle. Equilibrium as well as rate zonal centrifugation suggest that this denser [3H] retinoid-containing vesicle may represent endoplasmic reticulum. We have compared the intracellular transport of chylomicron remnant [3H]retinyl ester and 125I-asialofetuin. The receptor-mediated endocytosis of asialoglycoproteins in rat liver parenchymal cells is a thoroughly studied system. Our results suggest that the [3H] retinoid and 125I-asialofetuin follow the same path initially to the endosomes. After transit in endosomes, the intracellular transport differs. While asialofetuin is transported to the lysosomes, the retinoid is probably transferred to the endoplasmic reticulum.     

Characteristics of destructive-regenerative processes in the kidneys of albino rats in conditions of necronephrosis caused by corrosive sublimate

Study of serial semi-thin (0.5 micron) metacrylate and paraffinic (8 microns) of rat kidney sections 6, 12, 24 and 48 h after subcutaneous injection of mercury bichloride at a dose of 0.6 mg/100 g bw has revealed that injury to different parts of the canalicular nephron is of heterogeneous character. The proximal part of the nephron demonstrates both complete and partial necrosis of nephrocyte cytoplasm. The distal parts of the nephron and collecting tubules are characterized by partial necrosis of the apical cytoplasm. Within the period between 12 and 24 h after the mercury bichloride injection, intracellular reparative processes are observed, in addition to destruction, in partially damaged but viable nephrocytes, which is confirmed by the enlargement of the nucleolic size. Regeneration of the tubular epithelium due to cellular restoration was unmarked 24 h after the mercury bichloride injection.     

Effect of bromocriptine on prostacyclin release and cyclic nucleotides on rat aortic and uterine tissues

The effect of bromocriptine mesylate on cyclic nucleotides and PGI₂ release by rat aortic and uterine tissues was investigated. Treatment of rats with bromocriptine (10 mg kg⁻¹ I.P. daily for 14 days) increased PGI₂ release by the thoracic aorta from 0.67 ± 0.02 to 1.4 ± 0.03 ng/mg wet tissue (P < 0.001; n = 6). This increase was antagonized by treatment with sulpiride (15 mg kg⁻¹). Incubation of the arterial tissue with bromocriptive (50 ug ml⁻) in vitro also stimulated PGI₂ release. Mepacrine (160 μg ml⁻) significantly decreased both basal and stimulated PGI₂ release. Incubation of myometrial tissue from pregnant rats with bromocriptine (50 μg ml⁻¹) in vitro significantly decreased PGI₂ release from 1.25 ± 0.07 to 0.60 ± 0.08 ng/mg wet tissue (P < 0.05, n = 6).It also elevated uterine cAMP from 40 ± 2 to 64 ± 3 pmoles/100 mg wet tissue. Both effects were antagonized by sulpiride. Bromocriptine did not affect uterine cGMP or the cyclic nucleotides in the aorta. It is concluded that the increase in aortic PGI₂ was mediated via activation of dopamine D-2 receptors that stimulate phospholipase A₂ enzyme. The decrease in myometrial PGI₂ release may be related to the increase in uterine cAMP resulting from activation of dopamine D-1 receptors. Previous studies suggested a role for PGI₂ in implantation in the rat. The results suggest that the inhibitory effèct on uterine PGI₂ may underlie the reported inhibition of bromocriptine on implantation. On broad basis, the decrease in uterine PGI₂ together with the reported luteolytic effect of bromocriptine point to a potential role for the compound in postcoital contraception.     

Circumsporozoite protein of Plasmodium berghei: gene cloning and identification of the immunodominant epitopes.

The gene encoding the circumsporozoite (CS) protein of the rodent malaria parasite Plasmodium berghei was cloned and characterized. A cDNA library made from P. berghei sporozoite RNA was screened with a monoclonal antibody for expression of CS protein epitopes. The resulting cDNA clone was used to isolate the CS protein gene from a lambda library containing parasite blood-stage DNA. The CS protein gene contains a central region encoding two types of tandemly repeated amino acid units, flanked by nonrepeated regions encoding amino- and carboxy-terminal signal and anchorlike sequences, respectively. One of the central repeated amino acid unit types contains the immunodominant epitopes.     

Glucose transport in human red cell membranes. Dependence of age, ATP, and insulin

Glucose self-exchange flux (Jex) and net efflux (Jnet) in human red cells and ghosts were studied at 25 degrees C and pH 7.2 by means of the combined use of the Millipore-Swinnex filtering method and the continuous flow tube method to show the dependence of time of storage after aspiration, ATP and insulin. In fresh cells (RBC), ghosts (G), ghosts with 2 mM ATP (G +), and cells stored at 4 degrees C greater than 60 days (OC) both Jex and Jnet follow simple Michaelis-Menten kinetics where J = Jmax X Ci X (K1/2 + Ci)-1. Jmaxex and Jmaxnet (nmol X cm-2 X s-1), respectively, was: (RBC) 0.27 and 0.19, (G) 0.24 and 0.27, (G +) 0.23 and 0.24, (OC) 0.23 and 0.20. K1/2,ex and K1/2,net (mM), respectively, was: (RBC) 7.5 and 1.3, (G) 4.8 and 14.2, (G +) 11.6 and 6.8, (OC) 3.8 and 9.0. In ghosts, the ATP-dependent fraction of the permeability shows a hyperbolic dependence on glucose concentrations lower than 80 mM. Insulin up to 1 microM had effect on neither Jex nor Jnet in RBC. Based on reported values of cytochalasin B binding sites the turnover rate per site in RBC appears to be as high as in maximally insulin-stimulated fat cells. Our results suggest that the number of transport sites remains constant, independent of age, ATP and insulin.     

Beta 2-receptors in the rat anterior pituitary mediate adrenergic stimulation of prolactin release

As previously shown, the beta-adrenergic agonists isoproterenol, epinephrine and norepinephrine stimulate prolactin (PRL) release from superfused rat anterior pituitary cell aggregates. In order to further characterize the beta-adrenergic response in this tissue preparation, the effects of various beta-adrenergic agents were investigated. The beta 2-agonist, zinterol, stimulated PRL release at concentrations more than 4 orders of magnitude lower than prenalterol, a beta 1-agonist with high potency in rat heart. The order of potency of the antagonists IPS 339 (beta 2), ICI 118.551 (beta 2), propranolol, sotalol, practolol (beta 1), metoprolol (beta 1) and H 35/25 for inhibition of beta-agonist-stimulated PRL release provided additional support for a beta 2-stimulatory effect. beta-Agonists were also capable of stimulating PRL release from superfused intact pituitaries. The beta-adrenergic response desensitized rapidly during prolonged exposure of the aggregates to beta-agonists.     

Structural requirements for diacylglycerols to mimic tumor-promoting phobol diester action on the epidermal growth factor receptor

The structural requirements for diacylglycerols to mimic the action of tumor-promoting phorbol diesters on the epidermal growth factor (EGF) receptor of A431 human epidermoid carcinoma cells were investigated. Five biological effects were considered: inhibition of high affinity 125I-EGF binding, change in the phosphorylation state of the EGF receptor, inhibition of the EGF-dependent tyrosine phosphorylation of the EGF receptor, inhibition of [3H]phorbol 12 beta, 13 alpha-dibutyrate binding, and stimulation of calcium- and phospholipid-dependent protein kinase (C-kinase) in vitro. A marked effect of the acyl chain length, 3-10 carbons, of symmetric sn-1,2-diacylglycerols was observed on their ability to mimic the effect of 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA). sn-1,2-Dipropanoylglycerol did not mimic the effects of PMA, but sn-1,2-didecanoylglycerol potently mimicked PMA action. A correlation was found between the ability of these diacylglycerols to stimulate the activity of C-kinase in vitro and to mimic the effects of PMA on the EGF receptor in intact cells. Analogues of sn-1,2-dioctanoylglycerol in which the 3' hydroxyl group was substituted with hydrogen, thio or chloro moieties were inactive when assayed for their ability to stimulate C-kinase in vitro and mimic PMA action in intact cells. We conclude that the hydroxyl group of a diacylglycerol is vital for the interaction with the phorbol diester receptor. The stringent correlation between the potency of the 11 diacylglycerol analogues tested to modulate C-kinase in vitro and to mimic PMA action in vivo provides strong evidence for the hypothesis that C-kinase plays a central role in the regulation of A431 cell EGF receptors by tumor-promoting phorbol diesters.     

Modulation of ornithine decarboxylase activity in the normal and regenerating rat liver by different doses of hydra peptide morphogen

The authors studied the anabolic effect of peptide morphogen of the hydra undecapeptide on normal and regenerating rat liver. Ornithine decarboxylase (EC 4.1.1.17) activity served as a marker. Intraperitoneal injection of the peptide into intact animals stimulated ornithine decarboxylase activity in a dose-dependent manner. In partially hepatectomized rats the peptide stimulated ornithine decarboxylase activity in the dose of 20 micrograms/kg body weight while greater doses inhibited the enzyme activity.