Phospholipid composition of cardiac (Na++K+)-ATPases from various species

Summary There is a difference in phospholipid composition of cardiac (Na⁺+K⁺)-ATPase preparations between species which are sensitive to ouabain and those which are not. Sphingomyelin is higher and phosphatidylcholine is lower in the enzymes from sensitive species than in those from insensitive ones. Lysophosphatidylcholine is detectable only in the latter preparations.     

Further evidence for the dissociation of digoxin-like immunoreactivity from Na+, K+-ATPase inhibitory activity

Summary The effects of adrenalectomy or nephrectomy, carried out one hour previously, on the levels of endogenous digitalis-like factors were determined in rat plasma. Factors were assayed by digoxin-like immunoreactivity and direct Na⁺, K⁺-ATPase inhibitory activity. Digoxin-like immunoreactivity significantly decreased one hour after bilateral ablation of adrenals, while Na⁺, K⁺-ATPase inhibitory activity remained unaltered. There were no changes in either activity one hour after bilateral nephrectomy. These results suggest that digoxin-like immunoreactivity may be derived from the adrenal gland or under adrenal control and the major substances detected by digoxin-like immunoreactivity and direct Na⁺, K⁺-ATPase inhibitory activity may be different.     

Biochemical and immunochemical evidence for the origin of the spermatophore material inGlossina morsitans morsitans Westwood

Summary Protein patterns in secretions from fully differentiated male accessory reproductive glands (ARG), spermatophore (Sp) and testes (Te) of the tsetse,Glossina morsitans morsitans Westwood, were determined by isoelectrofocusing. Isoelectrofocusing patterns of total ARG proteins and those of Sp were remarkably similar. At least 27 bands were detected in ARG and Sp. Out of these, 13 were major protein bands and isoelectrofocused in the pl range of 4 and 6.55. About 10 of these 13 were found to be acidic. Ouchterlony immunodiffusion and straight line immunoelectrophoresis showed that male accessory reproductive gland secretory proteins and spermatophore share common immunological characteristics which are different from those of the testes.     

Inhibition of the sodium pump does not cause a stoichiometric decrease of ATP-production in energy limited fish hepatocytes

In isolated goldfish hepatocytes underaerobic conditions the energy requirement for the sodium pump (calculated from Rb⁺ flux) is closely matched by the ouabain-sensitive fraction of oxygen consumption, whereas during in vitroanoxia (cyanide inhibition of the electron transport chain) the measured ATP demand of the sodium pump clearly exceeds ouabain-sensitive ATP production by anaerobic glycolysis. We conclude that when the energy status of cells is low, part or all of the ATP spared by the inhibition of a particular function may be used for fuelling other ATP-consuming functions.     

The effect of cyclic AMP on Na+ and K+ transport systems in mouse macrophages

Summary Exogenous cyclic AMP (cAMP) inhibits the Na⁺, K⁺-cotransport system and stimulates the Na⁺, K⁺-pump and Na⁺, Ca²⁺ exchange in mouse macrophages. These effects are enhanced by inhibition of phosphodiesterase with methylisobutylxanthine (MIX). MIX alone showed little or no effect. A similar response was observed after stimulation of endogenous production of cAMP by isoproterenol.     

Effect of various stressors on the levels of lipid peroxide,antioxidants and Na+, K+-ATPase actrivity in rat brain

The level of malondialdehyde (MDA), an index of lipid peroxidation, and the antioxidants superoxide dismutase (SOD) and glutathione (GSH), as well as the activity of Na⁺, K⁺-ATPase, were assessed in whole rat brain after immobilization, anemic hypoxia (NaNO₂) and 72 h starvation. The effect of these stressors on plasma glucose and corticosterone levels was also observed. Hypoxia and starvation stimulated the lipidj peroxide formation in braini as indicated by an increase in the level of MDA, being higher after starvation than hypoxia. Brain SOD activity was also increased in response to hypoxia and starvation while GSH content was only diminished ini hypoxia. However, neither MDA nor antioxidants were affected by immobilization. On the other hand, the activity of brain Na⁺, K⁺-ATPase was significantly increased by immobilization and hypoxia but decreased in starvation. A similar pattern of change was also observed in plasma glucose and corticosterone levels in response to these stressors. These results elucidate differences in the biochemical response of animals towards various types of stress, with increased lipid peroxide formation in hypoxia and starvation.     

Action of juvenile hormone on the follicle cells ofRhodnius prolixus: Evidence for a novel regulatory mechanism involving protein kinase C

Summary Juvenile hormone (JH) is known to act on the membranes of the follicle cells ofRhodnius, activating a specific Na⁺, K⁺-ATPase. This leads to a decrease in volume of the cells and the appearance of spaces between them (patency). The addition of an inhibitor of protein kinase C, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), to the medium in vitro inhibits the action of JH on the follicle cells. PDBU (phorbol-12,13-dibutyrate) mimics the action of JH in vitro and the response of the follicle cells to, PDBU is blocked by ouabain. It is concluded that the activation of protein kinase C is a required step in the chain of events leading to activation of the JH-dependent ATPase and set in train by the binding of JH to the membrane.     

Araplysillins-I and-II: Biologically active dibromotyrosine derivatives from the spongePsammaplysilla arabica

Summary Araplysillins-I and-II, two novel dibromotyrosine derivatives, were isolated fromPsammaplysilla arabica and their structure was elucidated by spectroscopic methods. They proved to be inhibitors of Na⁺/K⁺ ATPase and to have antimicrobial activity.     

The (Na++K+)-ATPase activity in brain of quaking mice

Summary The (Na⁺+K⁺)- and Mg²⁺-dependent ATPase distribution in several brain areas has been investigated in Quaking mutant mice characterized by myelin deficiency. A marked decrease of (Na⁺+K⁺)-ATPase activity has been found in limbic structures, hypothalamus and cerebellum. The Mg²⁺-dependent activity did not change. A possible involvement of the impairment of the (Na⁺+K⁺)-ATPase activity in the seizure susceptibility of this mice is discussed.Chargée de Recherche au CNRS.     

Lack of Na+,K+-ATPase expression in intercalated cells may be compensated by Na+-ATPase: A study on MDCK – C11 cells

The lack of Na⁺,K⁺-ATPase expression in intercalated cells (IC) is an intriguing condition due to its fundamental role in cellular homeostasis. In order to better understand this question we compared the activities of Na⁺,K⁺-ATPase and Na⁺-ATPase in two MDCK cell clones: the C11, with IC characteristics, and the C7, with principal cells (PC) characteristics. The Na⁺,K⁺-ATPase activity found in C11 cells is far lower than in C7 cells and the expression of its β-subunit is similar in both cells. On the other hand, a subset of C11 without α-subunit expression has been found. In C11 cells the Na⁺-ATPase activity is higher than that of the Na⁺,K⁺-ATPase, and it is increased by medium alkalinization, suggesting that it could account for the cellular Na⁺-homeostasis. Although further studies are necessary for a better understanding of these findings, the presence of Na⁺-ATPase may explain the adequate survival of cells that lack Na⁺,K⁺-ATPase. Received 09 July 2008; received after revision 03 August 2008; accepted 12 August 2008     

Purification from human plasma of endogenous dodium transport inhibitor(s)

Summary Na⁺, K⁺-ATPase inhibitors extracted from plasma of healthy human subjects displaced³H-ouabain binding to human erythrocytes and inhibited the Na⁺ efflux catalyzed by the Na⁺, K⁺-pump and unexpectedly the Na⁺, K⁺-cotransport system without alteration of the Na⁺, Na⁺-exchange or the Na⁺ passive permeability. This suggests the presence in healthy human plasma of endogenous factors with ouabain-like and furosemide-like activities.Acknowledgments. We are indebted to Dr M. A. Devynck for her advice on chemical measurements and to Dr R. P. Garay for his help with flux measurements     

Intracellular injection of cAMP and cGMP into snail neurones induces an increase in Na+-conductance

Summary Injection of cAMP and more rarely cGMP into the neurones of the snailHelix pomatia induces an increase in membrane conductance, membrane depolarization and excitation. The effect is theophylline-dependent and has a reversal potential near — 10 mV.     

The effect of physostigmine on (Na++K+)-ATPase activity in different rat brain regions

Summary The activity of (Na⁺+K⁺)-ATPase and acetylcholine esterase were folloed in rat brain cerebral cortex, caudate, thalamus, hippocampus and medulla after i.v. administration of physostigmine. Both enzymes were found to be inhibited in a dose-dependent manner. The most pronounced inhibition of (Na⁺+K⁺)-ATPase was found in caudate. where the highest activity of acetylcholine esterase is found.These studies were supported by a grant from the Union of Science of Republic Serbia, No. 40404-14.     

Altered K+ movement in liver mitochondria from alloxan diabetic rats

Summary Potassium movements were monitored in liver mitochondria from control and alloxan diabetic rats with a cationic electrode. There was net accumulation of K⁺ after Ca²⁺ addition to the mitochondria with the diabetic but not with the control.     

Decrease of K+ conductance underlying a depolarizing photoresponse of a molluscan extraocular photoreceptor

Summary An identified neurone in theOnchidium abdominal ganglion responds to light with a depolarizing generator potential, so that this neurone functions as an extraocular photoreceptor. The light-evoked depolarizing response is produced by a selective decrease in K⁺ conductance.     

Dual modes of 5-(N-ethyl-N-isopropyl)amiloride modulation of apical dipeptide uptake in the human small intestinal epithelial cell line Caco-2

Selective pharmacological Na⁺/H⁺ exchange (NHE) inhibitors were used to identify functional NHE isoforms in human small intestinal enterocytes (Caco-2) and to distinguish between direct and indirect effects on transport via the intestinal di/tripeptide transporter hPepT1. The relative potencies of these inhibitors to inhibit ²²Na⁺ influx identifies NHE3 and NHE1 as the apical and basolateral NHE isoforms. The Na⁺-dependent (NHE3-sensitive) component of apical dipeptide ([¹⁴C] Gly-Sar) uptake was inhibited by the selective NHE inhibitors with the same order of potency observed for inhibition of apical ²²Na⁺ uptake. However, 5-(N-ethyl-N-isopropyl) amiloride (EIPA) also reduced [¹⁴C]Gly-Sar uptake in the absence of Na⁺ and this inhibition was concentration and pH (maximal at pH 5.5) dependent. NHE3 inhibition by S1611 and S3226 modulates dipeptide uptake indirectly by reducing the transapical driving force (H⁺ electrochemical gradient). EIPA (at 100 μM) has similar effects, but at higher concentrations (>200 μM) also has direct inhibitory effects on hPepT1.Received 28 February 2005; received after revision 20 April 2005; accepted 20 May 2005     

Symbioramide,a novel Ca2+-ATPase activator from the cultured dinoflagellateSymbiodinium sp.

Summary A novel sphingosine derivative, symbioramide, has been isolated from the laboratory-cultured dinoflagellateSymbiodinium sp. as a sarcoplasmic reticulum (SR) Ca²⁺-ATPase activator, and its structure elucidated to be1 on the basis of spectral and chemical means.Acknowledgments. We thank Ms M. Hamashima and Ms A. Muroyama for their technical assistance.     

Selectivity of action between pyrethroids and combined DDT-pyrethroid insecticides on Na+ influx into mammalian neuroblastoma

Summary Several of the most active synthetic pyrethroid insecticides in the presence of sea anemone toxin II, induced a dose related influx of sodium ion into the C9 mouse neuroblastoma. The influx of sodium ion into this mammalian cell did not take place with a DDT analogue, EDO and several new combined DDT-pyrethroid insecticides, although these have been reported to cause excess sodium influx into arthropod axons, related to their insecticidal activity. This difference between species in the action of the new insecticides at the nerve sodium channel explains their low mammalian toxicity.