Biomedical subjects

D Lichtstein

Publications and source records attributed to D Lichtstein.

At least 37 records · Page 2Linked to original sources

PubMed1992

Modulation of rat olfactory bulb mitochondrial function by atrial natriuretic peptide.

Atrial Natriuretic Peptide (ANP) and receptors for ANP are widely distributed in many tissues and cell types in vertebrates. ANP has been shown to be internalized into the cytoplasm in several cell types and thus it raises the possibility that it may act on intracellular receptors. Displacement experiments of [125I]-ANP binding to rat olfactory bulb mitochondrial fraction demonstrated the presence of high affinity (Kd < 10(-9)M) binding sites (Bmax, 112 fmol/mg protein) in this preparation. The addition of ANP (10(-8) M) to this mitochondrial preparation resulted in a 25% increase in TPP+ accumulation, signifying a striking hyperpolarization of the mitochondrial membrane. In contrast ANP did not increase TPP+ uptake to liver mitochondrial preparations. This direct effect of ANP on Olfactory bulb mitochondrial membrane potential may underly the known effects of this hormone on steroidogenesis.

Animals↗

PubMed1992

Digitalis-like compounds in the toad Bufo viridis: tissue and plasma levels and significance in osmotic stress.

Digitalis-like compounds (DLC), constituents of animal tissues, are possible regulators of the Na+, K(+)-ATPase implicated in water and salt homeostasis. The distribution of DLC in the toad (Bufo viridis) was determined following methanol extraction and partial purification. DLC highest levels were found in the skin but it was also detected in the plasma and many internal organs. Short term (hours) exposure of the toad to hypertonic shock (1.5% NaCl) induced an increase in plasma osmolarity due to an increase in Na+ and Cl- levels. This treatment induced a transient, three fold, increase of DLC levels in the brain and transient reduction of its levels in the ventral skin. Acclimation of the toads to burrowing conditions for six weeks resulted in an increase in plasma osmolarity due to a large increase in plasma urea with a small increase in ion concentrations. Under these conditions DLC levels in the dorsal skin increased by 100% without alteration of its levels in the plasma, brain and ventral skin. DLC levels in the toad brain of control animals, showed a significant dependence on season, being highest in the summer and lowest in the winter. DLC levels in the skin peaked in May while the levels in the plasma were season independent. The changes in DLC levels induced by the short- as well as long-term perturbations in the animal environmental salinity together with the seasonal differences suggest that DLC in the toad is involved in water and salt homeostasis of these animals, but may also participate in other unknown functions.

Animals↗

PubMed1991

Effect of salt acclimation on digitalis-like compounds in the toad.

Digitalis-like compounds (DLC) were shown to be a normal constituent of the skin and plasma of toads. In order to assess the possible physiological role of these compounds in the toad, their levels were determined in the brain, plasma and skin following acclimation in different NaCl solutions. We demonstrate that an increase in salt concentrations in the animal medium from 0 to 1.2% decreased the levels of DLC in the brain by 50% without altering significantly its levels in the plasma and skin. An increase in medium salt concentration to 1.5% resulted in a 50% increase of DLC levels in the skin without changing its levels in the plasma or brain. These results suggest that skin and brain DLC may participate in the long-term salt and water homeostasis in the toad, while the plasma compound either participates in the short-term regulations of salt and water homeostasis or have some other, unknown, function.

Animals↗

PubMed1991

Comparison of the effects of a bufodienolide and ouabain on neuronal and smooth muscle preparations.

The effect of a bufodienolide (monohydroxy-14,15-epoxy-20,22-dienolide glycoside) purified from toad skin was compared with that of ouabain on 3H-noradrenaline release and on the tension of rabbit pulmonary arterial strips. This compound exerted an ouabain-like activity. The neuronal effects of this bufodienolide derivative on squid axon were also studied and compared with those of ouabain. Both compounds enhanced the resting and stimulation-evoked (2 Hz, 360 shocks) release of 3H-noradrenaline. Moreover, in the presence of either this bufodienolide or ouabain, the tension of the rabbit artery increased gradually, and the contraction evoked by electrical stimulation was potentiated. Both compounds enhanced, in a prazosin-sensitive way, smooth muscle responses to noradrenaline and to electrical stimulation. In higher concentrations, they contracted smooth muscle cells of pulmonary artery, an action which was insensitive to prazosin. The bufodienolide was about 8 times more active in inhibition of 22Na efflux than was ouabain, but did not affect Ca efflux, which is not sensitive to ouabain. It is therefore concluded that compounds with an inhibitory effect on Na+,K(+)-ATPase are able to affect chemical neurotransmission of blood vessels in such a way that in lower concentrations they potentiate the release of noradrenaline, and in higher concentrations they contract directly the smooth muscle. These findings indicate that such compounds if they are present in the circulation might be involved in the physiological regulation of blood pressure or in the genesis of hypertension.

Animals↗

PubMed1991

Identification of 11,13-dihydroxy-14-octadecaenoic acid as a circulating Na+/K(+)-ATPase inhibitor.

Two digitalis-like compounds (DLC) were purified to homogeneity from bovine plasma. The purification procedure consisted of organic extractions and batch chromatography followed by three subsequent separations using reverse-phase high-performance liquid chromatography. The presence of a DLC in the different fractions was monitored by their ability to inhibit (a) [3H]ouabain binding to rat brain synaptosomes, and (b) microsomal Na+/K(+)-ATPase activity. Using mass spectrometry and nuclear magnetic resonance spectroscopy the structure of one of the DLCs was identified as 11,13-dihydroxy-14-octadecaenoic acid. It is suggested that this new hydroxy, unsaturated, fatty acid derivative may regulate Na+/K(+)-ATPase activity under some physiological and pathological conditions.

Animals↗

PubMed1990

The "cellular state": the way to regain specificity and diversity in hormone action.

In contrast with the high specificity achieved in the effects of hormones and growth factors by their interaction with a large number of membrane receptors, a loss of information seems to take place due to the small number of second messenger systems. To retain specificity one has to consider the cellular state as defined in a state machine by a pattern of activity. Different molecular mechanisms are considered as possible candidates to establish such states following the initial ligand-receptor interaction and the activation of one or several second messengers.

Animals↗

PubMed1990

Volume regulation of nerve terminals.

Pinched-off presynaptic nerve terminals (synaptosomes) possess significant regulatory volume increase (RVI) and regulatory volume decrease (RVD) capabilities. Following a swelling induced by a hypotonic challenge, the synaptosomes regulate their volume and adjust it, in 2 min, to within 5% of its initial value (RVD) at an initial rate of -0.77 +/- 0.10%/s (mean +/- SEM). Following a shrinking induced by a hypertonic challenge, the synaptosomes also regulate their volume at an initial rate of 0.18 +/- 0.02%/s (RVI), resulting in a new steady state, reached within 5-10 min, with a synaptosomal volume below the original volume. The omission of Na+ or K+ ions from the extrasynaptosomal medium reduces the initial rate of RVI by 72.5 and 66.5%, respectively. The "loop diuretics" bumetanide and furosemide significantly inhibited the RVI of the synaptosomes. In contrast, ouabain, amiloride, or 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid did not have any significant effect on RVI parameters. Furthermore, bumetanide-sensitive 86Rb uptake by rat brain synaptosomes was stimulated threefold by a hypertonic perturbation of 30%. Thus we conclude that the RVI of synaptosomes is mainly due to a stimulation of the Na+, K+, Cl- co-transport system induced by the synaptosomal shrinking following the hypertonic challenge.

Animals↗

PubMed1989

A bumetanide-sensitive, potassium carrier-mediated transport system in excitable tissues.

The binding of [3H]-bumetanide to rat brain synaptosomes revealed the existence of two binding sites. The high affinity site (R1 = 46.6 fmoles/mg protein) binds bumetanide and furosemide with Kd1 of 13 nM and 1.5 microM respectively, while the low affinity site (R2 = 1.37 nmoles/mg protein) is characterized by Kd2 of 200 microM and 680 microM for bumetanide and furosemide, respectively. Bumetanide sensitive 86Rb uptake was 34 +/- 14.5, 38.3 +/- 1.4, 18.6 +/- 1.3 and 29.0 +/- 6.1% of total 86Rb uptake in synaptic plasma membrane vesicles, rat brain synaptosomes, Neuroblastoma N1E115 cell line and chick chest muscle cells, respectively. Furosemide and bumetanide inhibited 86Rb uptake to rat brain SPM- vesicles in a dose dependent fashion. Half maximal inhibition (IC50) was observed at 20 nM and 4 microM for bumetanide and furosemide, respectively. Bumetanide-sensitive transport was dependent on extravesicular sodium and chloride concentrations with a Km of 21 and 25 mM for the two ions, respectively. These results demonstrate the existence of a "loop diuretic" sensitive carrier-mediated K+ transport system in brain and other excitable cells.

Animals↗

PubMed1988

Ouabain induces secretion of proatrial natriuretic factor by rat atrial cardiocytes.

Neonatal rat atrial and ventricular cardiocytes in primary culture secrete proatrial natriuretic factor (proANF), the 126-amino acid precursor of atrial natriuretic factor (ANF). The cellular mechanisms of proANF secretion differ in the two cell types: atrial cardiocytes store proANF in abundant secretory granules before secretion, whereas ventricular cardiocytes secrete the precursor rapidly after synthesis. In this study, we used the Na+-K+-adenosinetriphosphatase (ATPase) inhibitor ouabain to investigate the functional significance of these differing secretory mechanisms. Ouabain increased immunoreactive ANF (iANF) secretion by atrial cardiocytes 1.5- to 2.4-fold. Metabolic labeling studies demonstrated that proANF was the form of iANF released in response to ouabain. Ventricular secretion of iANF was unaffected by the Na+-K+-ATPase inhibitor. These observations are consistent with a model in which atrial cardiocytes are able to release proANF via a regulated secretory pathway, whereas ventricular cardiocytes utilize a constitutive secretory pathway. The ability of ouabain to stimulate proANF secretion suggests that an increase in intracellular calcium concentration may promote fusion of secretory granules with atrial cell membranes thereby mediating exocytosis of stored proANF.

Animals↗

PubMed1988

Multiple interactions of unsaturated fatty acids with opiate and ouabain binding sites and beta-adrenergic sensitive adenylate cyclase system.

The unsaturated fatty acids oleic, linoleic and arachidonic inhibited binding of ligands to the ouabain, opiate, and beta-adrenergic plasma membrane receptors. Low concentrations of fatty acids slightly increased the binding of ouabain to its binding sites. The effect of these fatty acids on beta-adrenergic sensitive adenylate cyclase was more complex. 0.2-0.3 mM fatty acids increased adenylate cyclase activity, while higher concentrations of arachidonic and linoleic acids, but not oleic acid, inhibited basal, beta-agonist- and NaF-stimulated activities in membranes of A431 and C6 cells. To evaluate which aspects of the unsaturated fatty acid molecules might be responsible for the observed effects, myristic acid, monoolein and taurodeoxycholic acid were studied. They also inhibited binding to the opiate receptor. Myristic acid, did not inhibit ouabain binding, binding to beta-receptor, nor adenylate cyclase activity. Monoolein, had no inhibitory effect on ouabain binding but behaved similar to oleic acid in the beta-receptor/adenylate cyclase system. Taurodeoxycholic acid inhibited binding to all three receptors as well as adenylate cyclase activity. We conclude that the effects of unsaturated fatty acids on ligand binding and adenylate cyclase activity are the result of their multiple interactions with various molecular processes rather than any unique property of long chain unsaturated fatty acids, per se.

Adenylyl Cyclases↗

PubMed1987

A second look at the second messenger hypothesis.

Several hundred hormones, neurotransmitters, growth factors and other "first messengers" bind to specific cell membrane receptors and induce a myriad of effects: short term, transport, metabolic, mitotic and regulation of thousands of specific genes. Yet, less than a dozen "second messengers" have been clearly established to date. Even allowing for the discovery of a large number of additional second messengers, there remains a paradox in terms of information-transfer within the cell: how can so many specific signals produce so many effects through so few relatively nonspecific intermediates? We consider several possible solutions to this paradox, including the hypothesis that signal specificity is encoded in part in the primary structure of the receptor.

Adenylyl Cyclases↗

PubMed1987

Noradrenaline releasing effect of an ouabain-like compound on pulmonary artery.

The effect of ouabain and an endogenous ouabain-like compound (OLC) was studied on (3H)noradrenaline [3H)NA) release from rabbit pulmonary artery. Similarly to ouabain, OLC enhanced the release of (3H)NA in response to electrical stimulation. These findings are the first evidence that OLC is able to act presynaptically and enhance the amount of (3H)NA release per impulse. It is suggested that this mechanism might be involved in the physiological regulation of blood pressure or in the genesis of hypertension.

Animals↗

PubMed1987

Demonstration and characterization of two classes of cardiac glycoside binding sites to rat heart membrane preparations using quantitative computer modeling.

Cardiac glycoside binding to rat heart membrane preparations was measured by rapid filtration technique. The binding data were analyzed using quantitative computer analysis. The experimental results using [3H]-ouabain as the labeled ligand were consistent with a model in which cardiac glycoside specific binding occurs at two independent classes of sites. The high affinity sites were characterized by a dissociation constants of 40 nM, 50 nM, and 61 nM for ouabain, digoxin and digitoxin, respectively, with a binding capacity of 1.3 pmoles/mg protein. The lower affinity sites for ouabain were characterized by dissociation constants of 2.3 microM, 67 nM and 71 nM for ouabain, digoxin and digitoxin, respectively, with a binding capacity of 3 pmoles/mg protein. Potassium ions inhibit [3H]-ouabain binding in a dose dependent manner with an IC50 of 500 microM. Quantitative computer modelling indicated that potassium inhibits ouabain binding at both binding sites.

Animals↗

PubMed1987

The ouabain receptor in animal tissues and its endogenous ligand.

Cardiac glycosides bind to the Na+,K+-ATPase and inhibit its activity. Low concentrations (less than 10(-7) M) of ouabain stimulate the activity of Na+,K+-ATPase in whole homogenates of rat brain. The magnitude of this stimulation varies from 5 to 70%. The concentration of ouabain which induces maximal stimulation is also highly variable and ranges between 10(-9) to 10(-7) M. This stimulation may be explained by the presence of an endogenous ouabain-like compound (OLC) in the brain homogenate. Mammalian tissues and body fluids including brain, heart, kidney, plasma, urine and cerebrospinal fluid contain a unidentified OLC. An endogenous OLC was also demonstrated in toad skin and plasma. This compound was purified to homogeneity and identified using UV, NMR and Mass spectroscopies to be 3-hydroxy-14, 15-epoxy-20,22-dienolide glycoside (resibufogenin). Several reports have suggested that unsaturated fatty acids are the ouabain-like regulators of the Na+,K+-ATPase. Furthermore, Saline infusion to WKY rats, which was shown to increase OLC in the plasma causes also an elevation of free fatty acids. Thus, the interaction of fatty acids with several plasma membrane components was studied. Ouabain binding, opiate binding and binding to the beta-adrenergic receptor were all inhibited by micromolar concentrations of the unsaturated fatty acids, linoleic, oleic and arachidonic. Binding to the opiate receptor was inhibited with IC50 of 40-90 microM and binding to beta-adrenergic receptor with IC50 of 350-450 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Identification of a ouabain-like compound in toad skin and plasma as a bufodienolide derivative.

An ouabain-like compound (OLC) was purified from toad skin. The purification procedure consisted of three sequential separations on HPLC using amino and reverse phase chromatography. Using UV, NMR and Mass spectroscopy the structure of the purified material is suggested to be mono-hydroxy-14,15-epoxy-20,22-dienolide glycoside (resibufogenin). Evidence is presented that this compound is also present in the toad plasma. It is suggested that the endogenous bufodienolide derivative participates in the physiological regulation of the Na+,K+-ATPase activity.

Animals↗

PubMed1986

Endogenous "ouabain-like" activity in bovine plasma.

An endogenous inhibitor of the sodium pump has been detected and concentrated 1000-fold from bovine plasma. The steps of purification included deproteinization and extraction with methanol, removal of lipids by coextractions with a lipophilic solvent, desalting and further concentration by adsorption on C18-SepPack cartridges and HPLC fractionation on a weak anionic exchange column. The material isolated displaces 3H-ouabain from brain synaptosomes, inhibits red cell membrane Na,K-ATPase without inhibiting Mg-ATPase or Ca,Mg-ATPase. Deproteinization of plasma by boiling may lead to appearance of non-specific inhibitors. The procedures developed should now permit isolation of sufficient amount of material for further purification and structural characterization.

Animals↗

PubMed1986

Further characterisation of the inotropic effect of a bufodienolide glycoside--an endogenous ouabain like compound.

A ouabain like compound obtained from toad skin and plasma and identified to be a steroidal bufodienolide glycoside was found to displace ouabain from its binding site and to inhibit Na+-K+ ATPase, and have positive inotropic effects on cardiac muscle. The ionic and rate dependence of this positive inotropy was studied in the frog atrium. The effect was dependent on extracellular potassium, sodium, and calcium concentrations and on the rate of stimulation, which is similar to the properties of cardiac glycosides. Occasionally, the compound gave transient or even negative inotropic responses, as do the glycosides. The action potential configuration was also affected by the compound in the same complex pattern as is that of cardiac glycosides. It is concluded that the endogenous bufodienolide compound has the same physiological effects as cardiac glycosides. Since the same compound is present in toad plasma it may serve as an intrinsic humoral regulator of cardiac contractility. This study is the first detailed characterisation of the cardioactive properties of this compound.

Action Potentials↗

PubMed1986

Isolated rectal gland cells: oxygen consumption and hormonal stimulation.

Cells isolated from rectal glands of Squalus acanthias, using collagenase and hyaluronidase digestion, retained normal morphological characteristics as judged by light microscopy of 1-micron plastic sections. Their oxygen consumption per unit weight was comparable to that of intact rectal gland studied either in situ, or by isolated perfusion, as well as that of rectal gland slices. Cellular respiration was stimulated by dibutyryl cyclic AMP and theophylline or by vasoactive intestinal peptide which stimulate secretion of chloride by the intact gland. Stimulated oxygen consumption was inhibited by ouabain and bumetanide and was proportional to the concentration of sodium or chloride in the incubation solution. The oxygen consumption of these cells parallels the secretory and metabolic behavior of the intact rectal gland, suggesting that it reflects energy demands for ion transport. The relative ease with which a homogeneous preparation of viable and active cells can be obtained and the apparent preservation of many of their key functional characteristics make this preparation a useful tool for the study of hormone-stimulated ion transport.

Adenosine↗