The effects of sodium and amiloride on the motility of the caudal epididymal spermatozoa of the rat

Summary The forward motility of the rat caudal epididymal spermatozoa has been studied in different Na⁺ concentrations. When spermatozoa were suspended in a completely Na⁺-free solution, the forward motility suffered a progressive fall and after 3 h was completely suppressed. This effect was fully reversible on resuspending the spermatozoa in a solution containing Na⁺. Amiloride caused a fall in motility and the effect was similar to that of Na⁺ removal. The inhibition by amiloride of the motility was concentration dependent and the dose response curve showed an IC₅₀-value of about 5×10^–5 M. The role of Na⁺ influx in the maintenance of sperm motility was discussed.This work was supported by the World Health Organization.The technical assistance of Mr C.M. Li and the gift of amiloride from Merck, Sharp and Dohme are gratefully acknowledged.     

Announcement of the Editor-in-Chief

Announcement.  As decided in July 2005 we continue to publish once a year (in July) the names of the authors and the titles of the two most read (by Internet) Research Papers and Reviews published in Cell. Mol. Life Sci. the previous year. Thus we have the pleasure to provide you with the results of 2005. Research Articles  

Differences in membrane ion transport between hepatocytes from the periportal and the pericentral areas of the liver lobule

We studied the Na⁺/K⁺ pump, Na⁺/K⁺ ATPase activity, and oxygen consumption (QO₂) in hepatocytes isolated from the periportal (PH) and pericentral (CH) regions of the liver lobule, to provide an insight into the functional properties of these cells. Na⁺/K⁺ pump activity was determined using⁸⁶Rb⁺ (a functional analog of K⁺) and ouabain, a specific inhibitor of this transport system. Our results indicate the the Na⁺/K⁺, pump and Na⁺/K⁺ ATPase activity are significantly lower in CH than in PH, although basal ouabain-sensitive (OS) QO₂ was negligible in both of these cell preparations. However, OSQO₂ was significantly lower in CH than in PH when the Na⁺/K⁺ pump was activated using the ionophore nystatin in a Na⁺-containing medium. These results indicate that the differences in membrane ion transport exist between hepatocytes from different locations of the liver lobule.     

A histochemical demonstration of the Na++K+-ATPase activity in the thyroid and the effect of cyclic adenosine monophosphate (c-AMP)

Summary With a suitable modification of the Farquhar and Palade technique the Na⁺+K⁺-ATPase activity in guineapig thyroid is demonstrated. The addition of c-AMP (5×10^–6 M or 1.5×10^–5 M) to the incubation media produced an apparent intensification of the Na⁺+K⁺-ATPase activity in the thyroid.This work was supported by a grant from ZMNU of Serbia.     

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.     

Uptake of metabolic CO2 by the otoliths of the chick embryo

Riassunto Viene condotto uno studio sulla utilizzazione dell' NaHC¹⁴O₃ e C¹⁴H₃C¹⁴OC¹⁴OOH nel processo di calcificazione degli otoliti dell'embrione di pollo. I risultati delle indagini condotte hanno messo in evidenza la prevalente utilizzazione della CO₂ metabolica in tale processo.     

Zinc antagonizes the effect of botulinum type A toxin at the mouse neuromuscular junction

Summary Zn²⁺ (10–100 M) elevated the frequency of miniature end-plate potentials (MEPPs) in the mouse diaphragm. The effect did not depend on external Ca²⁺. Botulinum type A toxin (BTX_A, 50 ng/ml) abolished MEPPs almost completely within 30 min. Zn²⁺ (100 M) restored MEPPs and increased their frequency after they had been abolished by BTX_A in Ca²⁺-free solutions. The antagonistic effect of Zn²⁺ in the Ca²⁺-free solution was reduced by exposing the diaphragm to the toxin in the Ca²⁺-free solutions containing high K⁺. Thus, the action of BTX_A is probably enhanced by depolarization of the motor nerve terminals.     

Ionophoric activity of the antibiotic X.14547 A in the mitochondrial membrane

Summary Release of Ca⁺⁺, Mg⁺⁺ and K⁺ by the carboxylic ionophore X-14547 A was studied in the mitochondrial membrane. A comparison was made with A.23187 (Calcimycin) and X.537 A (Lasalocid A) under the same experimental conditions. It was shown that in this test system X.14547 A is primarily a K⁺ carrier comparable with X.537 A.     

On the phosphorylation of thiamine in the living animal

Riassunto Gli autori hanno preparato ATP³² dai muscoli di coniglio trattato preventivamente con fosfato di sodio radioattivo. Iniettando per via endovenosa l'ATP³² e tiamina a ratti albini è stato possibile mettere in evidenza, impiegando la tecnica cromatografica su carta, la formazione nel fegato di questi animali di DP³²T e TP³²T. Questi risultati dimostrano che nell'animale vivente ha luogo una diretta trasposizione di gruppi fosforici dall'ATP alla tiamina.     

Uptake of3H-GABA (γ-aminobutyric acid) and3H-leucine in the pancreatic islets and substantia nigra of the rat

Summary Isolated pancreatic islets and thin slices of substantia nigra (SN) of the rat were incubated in a medium containing³H-GABA or³H-leucine to test the activity of both tissues in the uptake of those substances. Pancreatic islets showed a low uptake of both³H-GABA and³H-leucine, but SN had a high activity in the uptake of³H-GABA, though not for³H-leucine. This suggests that GABA contained at high levels in the pancreatic islets plays some functional role other than in neurotransmission as in the central nervous system (CNS).     

Biochemical events associated with rapid cellular damage during the oxygen-and calcium-paradoxes of the mammalian heart

Summary The O_2– and Ca²⁺-paradoxes have a number of features in common and it is suggested that release of cytosolic proteins in both paradoxes is initiated by the activation of a sarcolemma NAD(P)H dehydrogenase which can generate a transmembrane flow of H⁺ and e^– and also oxygen radicals or recox cycling which damage ion channels and membrane proteins (phase I). Entry of Ca²⁺ through the damaged ion channels then exacerbates the damage by further activating this system, either directly or indirectly, and the redox cycling and/or oxygen radicals cause further damage to integral and cytoskeletal proteins of the sarcolemma resulting in microdamage to the integrity of the membrane (phase II) and the consequent release or exocytosis of cytoplasmic proteins and, under specialised condition, the blebbing of the sarcolemma. The system may be primed either by removal of extracellular Ca²⁺ or by raising [Ca²⁺]_i by a variety of measures, these two actions being synergistic. The system is initially activated in the Ca²⁺-paradox by the membrane perturbation associated with removal of extracellular Ca²⁺; prolonged anoxia in the metabolically active cardiac muscle causes a depletion of the ATP supply, particularly in the absence of glucose, and hence a rise in [Ca²⁺]_i in phase I of the oxygen paradox with the consequent activation of the NAD(P)H oxidase at the sarcolemma. Oxygen radicals are probably generated in both paradoxes and may have a partial role in the genesis of damage, but are not essential in the Ca²⁺-paradox which continues under anoxia. Massive entry of Ca²⁺ also activates an intracellularly localised dehydrogenase (probably at the SR) which produces myofilament damage by redox cycling.     

Experiments on the mechanism of the inhibition of mitochondrial Ca2+ transport by La3+ and ruthenium red

Summary The effects of La³⁺ and ruthenium red on the energy-linked uptake of Ca²⁺ mediated by a synthetic neutral Ca²⁺ ionophore have been investigated in rat liver mitochondria. The results indicate that unspecific surface charge effects do not play a major role in the mechanism of inhibition of mitochondrial Ca²⁺ transport by La³⁺ and ruthenium red.Acknowledgments. The authors are indebted to Prof. W. Simon, ETH Zurich, for having provided samples of the synthetic neutral Ca²⁺ ligand, and to M. Mattenberger for the valuable technical assistence. The work was supported by a grant of the Swiss Nationalfonds (grant No. 3.1720.75).     

Concerning the ionic basis of presynaptic inhibition

Summary The superfused rat cuneate nucleus has been used to investigate the sensitivity of primary afferent terminals and of evoked primary afferent depolarization (PAD) to alterations in extracellular K⁺ and Cl^– ion levels. Results indicate that PAD is caused by an efflux of Cl^– from primary afferent terminals rather than by an increase in extracellular 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 strychnine on the electroretinogram of the isolated rabbit retina

Zusammenfassung Strychnin in einer Konzentration von 3×10^–6 bis 3,5×10^–5 M/l verursacht eine vorübergehende Vergrösserung derb-Welle des ERG der isolierten Kaninchennetzhaut, in einer Konzentration von 7×10^–5 bis 7×10^–4 M/l verkleinert es dieb-Welle. Aus den Ergebnissen wird geschlossen, dass die Substanz zumindest teilweise schon auf die Schicht des zweiten Neurons wirkt.     

ATPase in the normal and dystrophic developing retina of the rat

Riassunto Viene descritto un aumento significativo dell'attività specifica dell'ATPasi (attività/mg proteine) durante lo sviluppo post-natale della retina in ratti normali ed in ratti con retinite pigmentosa ereditaria. Il rapporto tra attività ATPasica in presenza di Mg⁺⁺-Na⁺-K⁺ ed attività ATPasica in presenza di Mg⁺⁺ non varia nella retina normale, mentre esso va incontro ad un precoce declino durante lo sviluppo della retina distrofica. Il significato di questi dati è discusso molto brevemente.     

The action of ouabain in promoting the release of catecholamines

Summary It is suggested that ouabain promotes catecholamine release by causing a rise in intracellular Na⁺ which, in turn, causes an elevated steady-state level of intracellular Ca²⁺. It is suggested that the Na⁺–K⁺-ATPase is not directly involved in exocytosis at either adrenergic or cholinergic synapses.     

A note on the evolution of the transducer mechanism of the vertebrate retinal rod

Summary The Ca²⁺-gating mechanism that is the key component of membrane excitability in Paramecium has recently been localized on the cilia of this animal. Such a finding shows how the change in Ca²⁺ permeability (which is the probable consequence of the photoisomerization of rhodopsin) of the discs of the outer segments of the retinal rods could have evolved.     

Phosphoramidon enhances allatostatin-mediated inhibition of juvenile hormone biosynthesis in the corpora allta of the cockroach,Diploptera punctata

Use of the enkephalinase inhibitor phosphoramidon in the in vitro radiochemical assay for juvenile hormone biosynthesis enhanced allatostatin-mediated inhibition of hormone production by corpora allata of the cockroach,Diploptera punctata. Significant increases in inhibition in day 2 virgin female CA by AST 1 (at 10^–7 M) and AST 4 (10^–8–10^–7 M) were observed in the presence of phosphoramidon (10^–5M or greater). No significant increases in inhibition were seen in CA from day 6 mated females with AST 4 (10^–9–10^–7M) and phosphoramidon combined. Phosphoramidon alone had no effect on JH biosynthesis. Analysis of allatostatin content of the CA, as determined by ELISA, revealed that addition of phosphoramidon to the medium increased the endogenous allatostatin conten in CA of virgin and mated females. The similarity in primary structure between allatostatins and enkephalin-like peptides and their similar distribution makes it probable that phosphoramidon acts by preventing breakdown of allatostatins within the CA.     

Measurement of the biliary tree volume in the rat under Tm-conditions

Summary Biliary tree capacities determined under Tm-conditions using³⁵S-sulfobromophthalein sodium,^35S-sulfobromophthalein glutathione, and¹⁴C-taurocholate sodium as markers exceeded markedly the biliary volumes reported until now. This may have been caused at least partly by a more homogenous distribution of the marker substance throughout the liver parenchyma in contrast to simple bolus injection studies.