Involvement of thiols in the induction of inward current induced by silver in frog skeletal muscle membrane

Exposure of voltage-clamped frog skeletal muscle fibres to silver caused a maintained inward current which could be carried by Ca²⁺, Mg²⁺ or Na⁺. Inorganic Ca²⁺ channel blockers and dithiothreitol (SH reducing agent) diminished this current, but a Na⁺ channel blocker did not. Thus, silver activates the Ca²⁺ channel by acting on SH groups in a Ca²⁺ channel protein.     

Studies of total and protein-bound plasma Mg++ in wild and hatchery-reared coho salmon smolts in freshwater and in seawater

Summary Total plasma Mg⁺⁺ and Ca⁺⁺, Mg⁺⁺ in erythrocytes as well as protein-bound plasma Mg⁺⁺ were investigated in wild and hatchery-reared smolts. The proportion of plasma Mg⁺⁺ which was bound to plasma protein did not change significantly during entry into seawater, even though the in vitro addition of exogenous Mg⁺⁺ to the plasma showed that additional binding was possible.     

Differences in in vitro incorporation of tritiated deoxycytidine and tritiated thymidine into human lymphocytes

Summary Human lymphocytes stimulated in vitro by PHA or PWM incorporate³H-CdR into DNA, but less well than³H-TdR. More³H-CdR is incorporated in populations enriched for T cells. No³H-CdR is used by cells stimulated by lipopolysaccharides under circumstances in which³H-TdR is incorporated. We conclude that human T cells and B cells differ in their ability to use³H-CdR.     

The role of calcium in aggregation and development ofDictyostelium

Changes in cytosolic Ca²⁺ play an important role in a wide array of cell types and the control of its concentration depends upon the interplay of many cellular constituents. Resting cells maintain cytosolic calcium ([Ca²⁺]_i) at a low level in the face of steep gradients of extracellular and sequestered Ca²⁺. Many different signals can provoke the opening of calcium channels in the plasma membrane or in intracellular compartments and cause rapid influx of Ca²⁺ into the cytosol and elevation of [Ca²⁺]_i. After such stimulation Ca²⁺ ATPases located in the plasma membrane and in the membranes of intracellular stores rapidly return [Ca²⁺]_i to its basal level. Such responses to elevation of [Ca²⁺]_i are a part of an important signal transduction mechanism that uses calcium (often via the binding protein calmodulin) to mediate a variety of cellular actions responsive to outside influences.     

Role of bile in intestinal absorption of203Pb in rats

Summary The author studied absorption of²⁰³Pb after administering intraduodenally²⁰³Pb eliminated with bile. The results obtained were compared with absorption of203Pb administered into the duodenum as²⁰³PbCl₂ in rats forming 2 groups, one with bile ducts cannulated, the other intact. It was found that bile played an important role in absorption of Pb from the gastrointestinal tract. Absorption of Pb²⁰³ is significantly reduced if the bile is drained off by means of a canula.     

Enhanced susceptibility of T lymphocytes to oxidative stress in the absence of the cellular prion protein

The cellular prion glycoprotein (PrP^C) is ubiquitously expressed but its physiologic functions remain enigmatic, particularly in the immune system. Here, we demonstrate in vitro and in vivo that PrP^C is involved in T lymphocytes response to oxidative stress. By monitoring the intracellular level of reduced glutathione, we show that PrP^−/− thymocytes display a higher susceptibility to H₂O₂ exposure than PrP^+/+ cells. Furthermore, we find that in mice fed with a restricted diet, a regimen known to increase the intracellular level of ROS, PrP^−/− thymocytes are more sensitive to oxidative stress. PrP^C function appears to be specific for oxidative stress, since no significant differences are observed between PrP^−/− and PrP^+/+ mice exposed to other kinds of stress. We also show a marked evolution of the redox status of T cells throughout differentiation in the thymus. Taken together, our results clearly ascribe to PrP^C a protective function in thymocytes against oxidative stress.     

Lack of pressor effect of dopamine in the pentobarbital-anesthetized rat

Summary The blood pressure and heart rate responses to intravenous dopamine infusion at 2.5, 5.0 and 10.0 g·min^–1·100 g^–1 were studied in conscious and pentobarbital-anesthetized Sprague — Dawley rats. In the conscious rats, dopamine caused a significant dose-related increase in the mean arterial blood pressure which was abolished in the anesthetized rats. The heart rate increased significantly only at the highest dose infused. The responses to equipressor doses of noradrenaline (40 ng·min^–1·100 g^–1) and phenylephrine (1.0 g·min^–1·100 g^–1) were also suppressed in the anesthetized rats. The results suggest that pentobarbital anesthesia depresses the blood pressure response to dopamine infusion in the rat through a depression of activation of alpha-adrenoceptors.16 June 1986     

Antagonism of prostaglandin-induced cyclic AMP accumulation in the rat anterior pituitary in vitro by somatostatin analogues

Summary The PGE₂-induced cyclic AMP accumulation in the rat anterior pituitary in vitro is inhibited by [desamino¹]-, [desamino¹] [descarboxy¹⁴] and [d-Lys⁴]-somatostatin similarly to somatostatin, while the [descarboxy¹⁴]-somatostatin exhibits reduced activity; [d-Lys⁹]-somatostatin is ineffective at a higher concentration.The authors acknowledge the technical assistance ofG. Alexander. F. Bellini, D. Mangerel andJ. Rochon and thank Dr.G. Schilling and his associates for the analytical data.     

Direct inhibition of phospholipid scrambling activity in erythrocytes by potassium ions

The exposure of phosphatidylserine (PS) at the cell surface plays a critical role in blood coagulation and serves as a macrophage recognition moiety for the engulfment of apoptotic cells. Previous observations have shown that a high extracellular [K⁺] and selective K⁺ channel blockers inhibit PS exposure in platelets and erythrocytes. Here we show that the rate of PS exposure in erythrocytes decreases by ~50% when the intracellular [K⁺] increases from 0 to physiological concentrations. Using resealed erythrocyte membranes, we further show that lipid scrambling is inducible by raising the intracellular [Ca²⁺] and that K⁺ ions have a direct inhibitory effect on this process. Lipid scrambling in resealed ghosts occurs in the absence of cell shrinkage and microvesicle formation, processes that are generally attributed to Ca²⁺-induced lipid scrambling in intact erythrocytes. Thus, opening of Ca²⁺-sensitive K⁺ channels causes loss of intracellular K⁺ that results in reduced intrinsic inhibitory effect of these ions on scramblase activity. Received 11 September 2008; received after revision 17 October 2008; accepted 27 October 2008     

Possible role of intestinal alkaline phosphatase activity in thiamine transport

Summary Thiamine deficiency caused a marked decrease of intestinal alkaline phosphatase (al-Pase) activity, but had no effect on the Ca⁺⁺-ATPase activity and Ca⁺⁺-absorption in rats. The al-Pase activity was significantly decreased 1 h after oral administration of ethanol at 0.5 and 2.5 g/kg. In contrast, Mg⁺⁺-, Ca⁺⁺- and (Na⁺+K⁺)-ATPase activities did not change after the administration of ethanol. These findings show that the al-Pase activity, unlike the Ca⁺⁺-ATPase activity, is not related to Ca⁺⁺-absorption. A possible role of al-Pase activity in the active transport of thiamine in the intestine was discussed.     

Photoreactivation of UV damage in culturedDrosophila cells

Summary Cell survival and photoreactivation of 254 nm ultraviolet (UV) light damage in a wild typeDrosophila cell line was assayed by colony formation in liquid medium. F_o, F_q, and extrapolation number for the exponential portion of survival curves are 21 J/m², 3.6 J/m², and 1.5 for non-photoreactivated cells and 110 J/m², 11.2 J/m², and 1.3 for those exposed to photoreactivating light. Maximal photoreactivation occurs at the 100 J/m² region of the curve. At 10 and 50% survival, 75–80% of the UV damage was photoreactivable.     

Time course of the distribution of in vivo administered89Sr++ in rat liver subcellular fractions

Riassunto É stata studiata la distribuzione dello⁸⁹Sr⁺⁺ nelle frazioni subcellulari di fegato di ratto. Nei primi secondi dopo l'iniezione, la maggior parte dello⁸⁹Sr⁺⁺ si trova nei mitocondri. In alcuni minuti, la radioattività diminuisce nei mitocondri ed aumenta nel reticolo endoplasmico e nella fase solubile. Lo⁸⁹Sr⁺⁺ viene probabilmente trasferito da una struttura cellulare all'altra; i mitocondri ed il reticolo endoplasmico svolgono ruoli distinti nella deposizione dello Sr⁺⁺ nella cellula epatica.

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This research was supported by the U.S. Public Health Service (Grant No. RO5 TW-00216) and by the Italian National Research Council, with the skilled technical assistance of MissDaniela Ceccarelli.     

Inhibition of hepatic Na+, K+-adenosinetriphosphatase in taurolithocholate-induced cholestasis in the rat

Summary Na⁺, K⁺-adenosinetriphosphatase (Na⁺, K⁺-ATPase) activity was decreased in liver plasma membranes from rats in which cholestasis had been induced by i.v. administration of sodium taurolithocholate (5 moles/100 g b. wt). Incubation of liver plasma membranes with taurolithocholate (10–1300 M) caused significant and dose dependent reductions of Na⁺, K⁺-ATPase activity at taurolithocholate concentrations above 100 M. These findings lend support to the hypothesis that cholestasis induced by monohydroxy bile acids is at least partially the result of an inhibition of hepatic Na⁺, K⁺-ATPase activity.This work was supported by the Swiss National Science Foundation.The authors thank Mr H. Sägesser and Miss B. Schütz for technical assistance.     

A reappraisal of the hormonal regulation of larval fat body histolysis in femaleDrosophila melanogaster

The histolysis of larval fat body cells in adult femaleDrosophila melanogaster was examined in wild type and mutant animals. The fat body cells of wild type (Canton-S),apterous ^56f homozygotes,apterous ^78jts homozygotes and heterozygotes,apterous ⁴/+, ecdysoneless¹ homozygotes and heterozygotes all underwent histolysis normally during the 72 h following adult eclosion. Only in the case ofap ⁴/ap⁴ adults did the cells fail to histolyze normally. The fat body cells of both diapausing and non-diapausing wild type females underwent histolysis at the same rate. Attempts to demonstrate histolysis in vitro were unsuccessful, even in the presence of juvenile hormones (JHs), larval ring glands, or adult ovaries. In all strains other than theap ⁴ homozygotes, a significant proportion of larval fat body cells were dead at any time while theap ⁴/ap⁴ animals, almost all cells remained viable. It is postulated that fat body cell lysis following eclosion is not a JH-mediated event, but is elicited by an as yet unidentified factor(s), possibly originating in the ovary.     

Cell-to-cell transmission in the activation of in situ nematocytes in acontia ofCalliactis parasitica

Summary It is reported that Ca²⁺-induced discharge of in situ nematocytes of acontia ofCalliactis parasitica can occur by cell-to-cell transmission along the acontial filament at a speed that averages 9.8·10^–3 cm^–1. The discharge is preceded by protrusion of nematocytes that proceeds along the acontium at a slightly higher speed.     

Blockade by zinc ions of K+-induced contraction and calcium in guinea pigTaenia coli

Preincubation with 0.3 mM Zn²⁺ markedly inhibited both the tonic response and Ca²⁺ binding at low affinity sites induced by K⁺ (60 mM), with smaller effects on the phasic response and the high affinity Ca²⁺ sites, inTaenia coli. However, when the muscle was kept in Zn²⁺-containing medium following the first stimulation with the K⁺, the phasic response and the high affinity Ca²⁺ sites were more severely inhibited during the second stimulation with K⁺. This probably indicates that Zn²⁺ reduced the tonic tension response to K⁺ mainly by inhibiting Ca²⁺ influx at the cell membranes ofTaenia coli. However, when Zn²⁺ is continuously present, Ca²⁺ is not supplied at the storage sites and is not available for the phasic response to a second stimulation with K⁺.     

Effect of enkephalins in the presence of the antibiotic bacitracin in the longitudinal muscle strip preparation from guinea-pig ileum

Summary The antibiotic bacitracin (5×10^–5–4×10^–4 M) increases the inhibition of the contractile response caused by both enkephalin release and direct application of Met-enkephalin 5×10^–7 M in the longitudinal muscle strip preparation from guinea-pig ileum. This effect is attributed to an inhibition of enkephalin degrading peptidases by bacitracin.     

Effect of ouabain on volume regulation of rabbit kidney cortex slices in hypo-osmotic media

Summary The volume regulation process at work in rabbit kidney cortex slices submitted to hypo-osmotic media show both a swelling limitation and a volume readjustment phase. Swelling limitation is Na⁺ dependent and is blocked by ouabain 10^–3 M. There is, however, no need to implicate the activity of a ouabain sensitive Na⁺/K⁺ pump in this process.This work has been aided by a grant 1.5.422.82F from the FNRS to R.G. We wish to thank Mr J.M. Theate for his skilful assitance.     

Drug interactions in intestinal absorption of3H-digitoxin in rats

Summary The absorption of³H-digitoxin from perfused rat small intestine was inhibited by probenecid (1.0×10^–2 M), ethacrynic acid (0.5×10^–3 M), and mersalyl (8.0×10^–3 M) indicating that digitoxin absorption is at least partly an active process.     

Two phorbol ester receptor affinities in partially transformed human urothelial cells and decrease of receptor binding in desensitized cells

The presence of specific binding sites for phorbol esters was studied in a transformed but non-tumorigenic human urothelial cell line HCV-29 by assay of specific binding of³H-phorbol-12,13-dibutyrate (³H-PDBu) to intact living cells.³H-PDBu bound specifically to HCV-29 cells in a saturable and competitive manner. Scatchard plot analysis of specific binding yielded a curved plot consistent with two binding sites with K_d of 11 nM and 102 nM, respectively. At saturation the corresponding PDBu binding capacities (B_max) were 8.8 pmol/10⁶ cells (5.2×10⁶ molecules bound per cell) and 2.8 pmol/10⁶ cells (1.7×10⁶ molecules bound per cell).³H-PDBu binding was displaced by biologically active phorbol ester tumor promoters such as 12-O-tetradecanoylphorbol-13-acetate (TPA) and mezerein,but not by tumor promoters such as L-tryptophan, anthranilic acid and sodium saccharin. In cells desensitized by pretreatment with 1 g/ml (2M) TPA or PDBu for 24 h the level of binding was reduced to 28% of the level in non-exposed cells. The ability of desensitized cells to bind³H-PDBu was gradually restored within 5–6 days. At the same time the cells became sensitive to the morphological alteration induced by PDBu. This suggests that desensitization of HCV-29 cells is due to a decreased receptor-ligand binding capacity probably associated with down regulation of the phorbol ester receptors.