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Biomedical subjects

L Brown

Publications and source records attributed to L Brown.

At least 325 records · Page 18Linked to original sources
PubMed1984

Cardiac glycoside receptors in cultured heart cells--II. Characterization of a high affinity and a low affinity binding site in heart muscle cells from neonatal rats.

The binding of [3H]ouabain has been studied in (Na+ + K+)-ATPase enriched cardiac cell membranes, as well as in cardiac muscle and non-muscle cells in culture--all obtained from hearts of neonatal rats. The binding has been correlated with ouabain-induced inhibition of (Na+ + K+)-ATPase (cardiac cell membranes) and the inhibition of active (86Rb+ + K+)-influx (cardiac muscle and non-muscle cells in culture). Furthermore, the effect of ouabain on the amplitude of cell-wall motion and contraction velocity has been studied in electrically driven cardiac muscle cells. In muscle and non-muscle cells, two classes of ouabain binding sites have been identified. In rat heart muscle cells, the high affinity binding site has a dissociation constant (KD) of 3.2 X 10(-8) M and a binding capacity (B) of 0.2 pmole/mg protein (80,000 sites/cell); the values for the low affinity binding site are: KD = 7.1 X 10(-6) M; B = 2.6 pmole/mg protein (10(6) sites/cell). The binding to both types of binding sites is depressed by K+ and abolished after heat denaturation of the cells. The kinetics of [3H]ouabain binding to rat heart muscle cells (association and dissociation rate constants, K+- and temperature-dependence of association and dissociation processes) have been characterized. In rat heart muscle and non-muscle cells, the binding of [3H]ouabain to the low affinity site results in inhibition of the (86Rb+ + K+)-influx (EC50 = 1.3 and 1.5 X 10(-5) M ouabain), a decrease in cell-K+ (EC50 = 1.9 and 1.4 X 10(-5) M) and an increase in cell-Na+ (10(-5)-10(-4) M). The ouabain-induced positive inotropic effect (increase in amplitude of cell-wall motion, increase in contraction velocity) in cardiac muscle cells is observed only at ouabain concentrations greater than or equal to 5 X 10(-6) M, and it is therefore probably attributed to occupation of the low affinity binding site. Coupling of occupation of the low affinity site by ouabain with drug-induced inhibition of the sodium pump and with drug-induced positive inotropic action is further substantiated by kinetic measurements. In contrast, occupation of the high affinity binding site does not produce any measurable inhibition of the sodium pump activity or positive inotropy.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Non-additive positive inotropic effects of amrinone and ouabain on cat papillary muscles.

Amrinone has been shown to produce haemodynamic benefits in digitalis-treated patients. Since amrinone is a positive inotropic agent on isolated heart muscle, these benefits may mean that amrinone increases the maximal ouabain-induced increase in force of contraction, without causing toxicity. We have therefore measured, in cat right ventricular papillary muscles, the inotropic effects of ouabain, amrinone alone and amrinone with a maximally effective, non-toxic ouabain concentration (2 X 10(-7) M). Ouabain is much more potent than amrinone (EC50-values: ouabain, 8 X 10(-8) M, amrinone, 1-2.8 X 10(-3) M). The highest amrinone concentration used (6 X 10(-3) M) produced a significantly lower increase in force of contraction than ouabain (2 X 10(-7) M) in the same muscles. After ouabain (2 X 10(-7) M) produced a stable effect, no further increase in force of contraction was observed with any amrinone concentration. Sustained arrhythmias were observed in five of six muscles at 3 X 10(-3) M amrinone with ouabain (2 X 10(-7) M), but in only one of these muscles with amrinone 3 X 10(-3) M alone. Since the positive inotropic effects of amrinone are not additive with those from a maximally effective ouabain concentration, the haemodynamic benefits seen in patients are probably due to non-cardiac effects of amrinone such as vasodilatation.

Aminopyridines↗
PubMed1984

Cardiac glycoside receptors in cultured heart cells--I. Characterization of one single class of high affinity receptors in heart muscle cells from chick embryos.

Binding of (3H)-ouabain and ouabain-induced inhibition of the sodium pump and of the (Na+ + K+)-ATPase have been characterized in cultured cardiac muscle and non muscle cells, as well as in cardiac cell membranes--all obtained from chick embryos. In both cell types, ouabain binds to a single type of binding sites in a temperature-dependent manner. The association rate but not the dissociation rate, is lowered by K+; specific binding is lost after heat-denaturation of the cells. Binding parameters (association and dissociation rate constants, activation energies for association and dissociation) are similar in muscle and non muscle cells. The dissociation constant of specific ouabain binding is 1.5 X 10(-7)M in cardiac muscle cells, and 1.9 X 10(-7)M in cardiac non muscle cells, the binding capacity being 2.6 and 2.1 pmoles/mg protein respectively. Specific binding of ouabain to the cells is coupled to inhibition of the sodium pump, as can be seen from ouabain-induced inhibition of active (86Rb+ + K+)-uptake, decrease in cellular K+, and increase in cellular Na+ (EC50 = 10(-7)-10(-6)M). The data obtained with cardiac cells are in good agreement with results found for ouabain binding (dissociation constant 4.3 X 10(-7)M) and (Na+ + K+)-ATPase inhibition (EC50 = 1.4 X 10(-6)M) in cardiac cell membranes prepared from the same tissue. Due to the experimental evidence it is concluded that the binding site for ouabain is identical with the cardiac glycoside receptor of these cells. In cardiac non muscle cells, binding of ouabain to its receptor is strictly coupled to inhibition of active K+-transport in a stoichiometric manner. In cardiac muscle cells, however, active K+-transport is inhibited by less than 10% when up to 40% of cardiac glycoside receptors have bound ouabain. It is assumed that this non-stoichiometric coupling of receptor occupancy and sodium pump inhibition in cardiac muscle cells may prevent substantial changes of Na+- and K+-contents in the heart in the presence of therapeutic levels of cardiac glycosides.

Animals↗
PubMed1984

Follicular carcinoma of the thyroid appearing as an intraluminal superior vena cava tumor.

Follicular carcinoma of the thyroid has the propensity for microscopic angioinvasion. Tumor extension into the great veins has been previously reported primarily as a postmortem finding. Most patients have a long history of a substernal goiter and appear initially with superior vena cava syndrome. We studied a case of intraluminal invasion of the superior vena cava by a follicular carcinoma of the thyroid, without superior vena cava syndrome. To our knowledge, this is the second reported case of a patient treated successfully by surgery.

Adenocarcinoma↗
PubMed1984

Two receptors for cardiac glycosides in the heart.

Specific binding of 3H-ouabain to rat cardiac cell membranes revealed a high affinity and a low affinity site. In order to test the pharmacological significance of these different types of binding sites, specific 3H-ouabain binding, force of contraction and 86Rb+-uptake were measured simultaneously in contracting cat papillary muscles and in guinea pig atria. The results in the digitalis sensitive cat shows one type of cardiac glycoside receptors with high affinity (KD approximately 10(-7) M) for ouabain. The occupation of this receptor runs parallel with an increase in force of contraction and an inhibition of 86Rb+-uptake. In the rather digitalis insensitive guinea pig, 3H-ouabain binding also runs parallel with increased force of contraction, 86Rb+-uptake, however, is only inhibited at toxic glycoside concentrations. Thus, in rat and guinea pig heart there exist at least two different digitalis receptors--the high affinity receptor seems to be coupled to inotropic effects, the low affinity receptor is linked to inhibition of (Na+ + K+)-ATPase.

Animals↗
PubMed1984

Two binding sites for ouabain in cardiac cell membranes.

Cardiac glycoside receptors were defined by simultaneous measurement of 3H-ouabain binding and its effects on cardiac cell membranes, contracting cardiac muscle and cultured cardiac cells. These measurements show that: Rat and guinea pig cardiac cell membranes have two specific ouabain binding sites. In both species, ouabain binding to the high affinity site on cell membranes correlates with the positive inotropic effect in contracting cardiac muscle. Inhibition of (Na+ + K+)-ATPase activity corresponds to binding to the low affinity site. This questions the hypothesis that (Na+ + K+)-ATPase inhibition is necessary for ouabain-induced positive inotropy. K+ may induce an heterogeneity in the ouabain binding sites of the digitalis-sensitive cat and human heart.

Animals↗
PubMed1984

Controlled release of microquantities of macromolecules.

A technique for insuring the controlled release of small amounts of macromolecules such as polypeptides from polymeric delivery systems is described. We show that incorporation of albumin in milligram quantities into these delivery systems can facilitate the sustained release of nanogram or microgram quantities of a model macromolecule such as inulin. The albumin-containing controlled-release polymers did not cause inflammation or tissue damage in two commonly used assay sites for certain biological growth factors such as tumor angiogenesis stimulators and inhibitors--the chick chorioallantoic membrane (CAM) and the rabbit cornea. The method reported here should be particularly suited to the delivery of purified growth factors which are active and usually obtainable in microgram or smaller amounts.

Animals↗
PubMed1984

Evidence for two kinetically and functionally different types of cardiac glycoside receptors in the heart.

Cardiac glycosides bind with high affinity to specific receptors in the heart. In cardiac cell membranes of most animal species and man, this glycoside-receptor binding is followed by a subsequent inhibition of the membrane-bound (Na+ + K+)-ATPase, the biochemical equivalent of the active Na+/K+-transport system. Most investigators, however, have been unable to find, as a consequence of the glycoside-(Na+ + K+)-ATPase interaction, an inhibited Na+ or K+ transport in intact cardiac tissue when using low but positive inotropic concentrations of cardiac glycosides. In electrically stimulated contracting rat or guinea pig cardiac muscle we determined two kinetically different 3H-ouabain binding sites. The high affinity/low capacity site is related to positive inotropy, whereas the low affinity/high capacity binding site is connected to an inhibition of the (Na+ + K+)-ATPase. Occupation of the low affinity sites with ouabain molecules was concomitant with an increased intracellular Na+ and loss of K+ as well as onset of arrhythmias. According to our experiments, there are at least two different types of ouabain binding sites, inhibition of the (Na+ + K+)-ATPase was not necessarily related to positive inotropy in rat and guinea pig heart.

Animals↗
PubMed1984

Relationship between ion requirements for respiration and membrane transport in a marine bacterium.

Intact cells of the marine bacterium Alteromonas haloplanktis 214 oxidized NADH, added to the suspending medium, by a process which was stimulated by Na+ or Li+ but not K+. Toluene-treated cells oxidized NADH at three times the rate of untreated cells by a mechanism activated by Na+ but not by Li+ or K+. In the latter reaction, K+ spared the requirement for Na+. Intact cells of A. haloplanktis oxidized ethanol by a mechanism stimulated by either Na+ or Li+. The uptake of alpha-aminoisobutyric acid by intact cells of A. haloplanktis in the presence of either NADH or ethanol as an oxidizable substrate required Na+, and neither Li+ nor K+ could replace it. The results indicate that exogenous and endogenous NADH and ethanol are oxidized by A. haloplanktis by processes distinguishable from one another by their requirements for alkali metal ions and from the ion requirements for membrane transport. Intact cells of Vibrio natriegens and Photobacterium phosphoreum oxidized NADH, added externally, by an Na+-activated process, and intact cells of Vibrio fischeri oxidized NADH, added externally, by a K+-activated process. Toluene treatment caused the cells of all three organisms to oxidize NADH at much faster rates than untreated cells by mechanisms which were activated by Na+ and spared by K+.

Biological Transport↗
PubMed1984

Binding of digitalis derivatives to beef, cat and human cardiac (Na+ + K+)-ATPase. Affinity and kinetic constants.

We have measured the potency of 17 digitalis derivatives on cardiac (Na+ + K+)-ATPase from the digitalis-sensitive species, beef, cat and human. The potencies are given as the dissociation constant (KD-value) calculated from the concentration of unlabelled compound which inhibited 3H-ouabain binding by 50%, or from Scatchard or Woolf analyses. KD-values calculated by these independent methods were similar. As previously noted, structure-activity relationship (SAR) studies show that the binding of the whole molecule is necessary for optimal potency. The 3H-labelled derivatives of five of these compounds were used to measure the association and dissociation rate constants with cardiac (Na+ + K+)-ATPase. The rate constants for cat and human cardiac (Na+ + K+)-ATPase were very similar. Further, KD-values on cat and human cardiac (Na+ + K+)-ATPase for the 17 compounds tested showed a close correlation (r greater than 0.99), indicating that the cat heart is a suitable model for digitalis effects on the human heart.

Animals↗
PubMed1984

Comparison of the affinity of human, beef and cat heart (Na+ + K+)-ATPase for different digitalis derivatives.

The potencies of eight digitalis derivatives, including two new derivatives of digitoxin, were determined on heart (Na+ + K+)-ATPase or erythrocytes from three digitalis-sensitive species, beef, cat and human. Three methods were used: inhibition of 3H-ouabain binding to give the dissociation constant (KD-value), or inhibition of (Na+ + K+)-ATPase activity or 86Rb+-uptake into human erythrocytes to give the IC50-values. The same order of potency was observed with all methods. The slopes of the concentration-response curves were similar for all compounds. For all compounds, the concentrations which inhibited 3H-ouabain binding by 50% caused about a 50% inhibition of (Na+ + K+)-ATPase activity. All three methods are suitable for determining the potency of new semisynthetic digitalis derivatives. The two new derivatives of digitoxin, 3"'-dehydrodigitoxin oxime and 3"'-dehydrodigitoxin methyloxime, were less potent than digitoxin but were of similar potency to ouabain.

Animals↗
PubMed1984

A comparison of the effects of ouabain, dihydroouabain and 3 alpha-methyldigitoxigenin glucoside on guinea pig left atria.

The effects of ouabain, dihydroouabain and 3 alpha-methyldigitoxigenin glucoside on force of contraction and 86Rb+-uptake were measured in contracting guinea pig left atria. Dihydroouabain and 3 alpha-methyldigitoxigenin glucoside were both about 40 times less potent than ouabain. All compounds gave approximately the same maximal increase in force of contraction. The results gave no evidence that either dihydroouabain or 3 alpha-methyldigitoxigenin glucoside has a greater therapeutic index than ouabain. All compounds showed similar effect on 86Rb+-uptake (no significant change at positive inotropic concentrations, significantly decreased 86Rb+-uptake only at toxic concentrations). These results imply that these three compounds have a similar mechanism of action.

Animals↗
PubMed1984

Comparison of the inotropic effects of some 5 alpha-cardenolides on guinea pig left atria.

The inotropic activity of eleven 5 alpha-cardenolides and six 5 beta-cardenolides was determined using guinea pig left atria and the results were compared with published data obtained from cat toxicity studies. The guinea pig atrial studies showed that the configuration of the A/B ring junction did not influence significantly the cardiotonic potency of digitoxigenin and its 5 alpha-epimer, uzarigenin, but was of significance with respect to the influence of substituent groups. Glucosidation decreased the potency of uzarigenin but increased that of digitoxigenin. By contrast, conjugation with rhamnose increased the activity of both uzarigenin and digitoxigenin. Cat toxicity data did not correlate well with that obtained using guinea pig atria, possibly because of the variable influence of pharmacokinetic factors applicable to the cat toxicity studies.

Animals↗
PubMed1984

Should the greater saphenous vein be preserved in patients requiring arterial outflow reconstruction in the lower extremity?

Two patient groups were studied to determine the need to preserve the greater saphenous vein during femoral outflow reconstruction for later aortocoronary bypass procedures. First, 74 patients were followed to the time of death or to a minimum of 5 years after femoral outflow reconstruction was performed. Only four patients (5.4%) underwent subsequent aortocoronary bypass. The previous outflow procedures had no adverse effect on the quality of aortocoronary conduit. Risk factors were analyzed to help predict the incidence of later coronary revascularization after femoral outflow reconstruction was performed. The second group that was analyzed included 500 nearly consecutive patients who underwent aortocoronary bypass. In 15 of these patients (3%), there was inadequate saphenous vein for conduit use. In no case was the inadequacy of saphenous vein due to its previous use as outflow conduit in the leg. Only seven patients (1.4%) had had an outflow reconstruction prior to aortocoronary bypass. In conclusion, continued use of adequate greater saphenous vein as femoral outflow conduit is justified despite the high incidence of coronary artery disease in these patients.

Adult↗
PubMed1983

Binding of dihydrodigitoxin to beef and human cardiac (Na+ + K+)-ATPase: evidence for two binding sites in cell membranes.

The specific binding of three cardiac glycosides, 3H-ouabain, 3H-digitoxin and 3H-dihydrodigitoxin, to beef cardiac (Na+ + K+)-ATPase was compared. Non-specific binding was defined as that in the presence of 0.1 mM unlabelled compound, or in the absence of ligands. The dissociation constants (KD-values) calculated from the inhibition of 3H-ouabain binding were: ouabain, 2.9 X 10(-9)M; digitoxin, 1.1 X 10(-9)M; and dihydrodigitoxin 2.7 X 10(-8)M. The concentrations which inhibited beef cardiac (Na+ + K+)-ATPase by 50% were: ouabain, 5.9 X 10(-9)M; digitoxin, 1.6 X 10(-9)M; and dihydrodigitoxin, 2.5 X 10(-8)M. Ouabain and digitoxin showed straight Scatchard plots for one site of high affinity (ouabain, KD = 2.6 X 10(-9)M; digitoxin, KD = 1.7 X 10(-9)M). However, dihydrodigitoxin gave a curved Scatchard plot. Analysis of this binding by the methods of M. J. Weidemann, H. Erdelt and M. Klingenberger (Eur. J. Biochem. 16, 313 (1970) for two binding sites gave the following results: for Mg2+,Pi-supported binding, the KD of the high affinity site was 1.6 X 10(-8)M with a capacity similar to that for ouabain of about 30 pmole/mg protein. For binding supported by Na+,ATP,Mg2+, the KD-value of the high affinity site was 5.3 X 10(-8)M of similar capacity. The low affinity binding site (KD = 4.0 X 10(-6)M for Mg2+,Pi; KD = 5.5 X 10(-6)M for Na+,ATP,Mg2+) bound about 350 pmole/mg protein. The low affinity site but not the high affinity site was also present in heat-denatured enzyme. Binding supported by Mg2+,Pi showed one low affinity site only for ouabain and dihydrodigitoxin in the presence of 200 mM Na+. The high affinity sites for these three cardiac glycosides were further characterized by measurement of the association and dissociation rate constants. The specific binding of 3H-ouabain and 3H-dihydrodigitoxin to human cardiac (Na+ + K+)-ATPase was measured. 3H-Ouabain showed a straight Scatchard plot for one high affinity site only (KD = 4.5 X 10(-9) M, capacity about 15 pmole/mg protein). 3H-Dihydrodigitoxin gave two binding sites: a high affinity site (KD = 1.8 X 10(-8) M) of similar capacity to ouabain, and a low affinity site (KD = 2.0 X 10(-6) M) of about 10-fold greater capacity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗