The beta-adrenergic receptor and adenylate cyclase

Neurovascular control during exercise in acute coronary syndrome patients with Gln27Glu polymorphism of β2-adrenergic receptor

Background

Gln27Glu (rs1042714) polymorphism of the β₂-adrenergic receptor (ADRB2) has been association with cardiovascular functionality in healthy subjects. However, it is unknown whether the presence of the ADRB2 Gln27Glu polymorphism influences neurovascular responses during exercise in patients with acute coronary syndromes (ACS). We tested the hypothesis that patients with ACS homozygous for the Gln allele would have increased muscle sympathetic nerve activity (MSNA) responses and decreased forearm vascular conductance (FVC) responses during exercise compared with patients carrying the Glu allele (Gln27Glu and Glu27Glu). In addition, exercise training would restore these responses in Gln27Gln patients.

Methods and results

Thirty-days after an ischemic event, 61 patients with ACS without ventricular dysfunction were divided into 2 groups: (1) Gln27Gln (n = 35, 53±1years) and (2) Gln27Glu+Glu27Glu (n = 26, 52±2years). MSNA was directly measured using the microneurography technique, blood pressure (BP) was measured with an automatic oscillometric device, and blood flow was measured using venous occlusion plethysmography. MSNA, mean BP, and FVC were evaluated at rest and during a 3-min handgrip exercise. The MSNA (P = 0.02) and mean BP (P = 0.04) responses during exercise were higher in the Gln27Gln patients compared with that in the Gln27Glu+Glu27Glu patients. No differences were found in FVC. Two months of exercise training significantly decreased the MSNA levels at baseline (P = 0.001) and in their response during exercise (P = 0.02) in Gln27Gln patients, but caused no changes in Gln27Glu+Glu27Glu patients. Exercise training increased FVC responses in Gln27Glu+Glu27Glu patients (P = 0.03), but not in Gln27Gln patients.

Conclusion

The exaggerated MSNA and mean BP responses during exercise suggest an increased cardiovascular risk in patients with ACS and Gln27Gln polymorphism. Exercise training emerges as an important strategy for restoring this reflex control. Gln27Glu polymorphism of ADRB2 influences exercise-induced vascular adaptation in patients with ACS.

Differential approach in selecting beta-adrenoblocker therapy for patients with chronic heart failure and anaemia

Currently, beta-adrenoblockers (β-AB) are regarded as one of the major medication classes in the treatment of patients with chronic heart failure (CHF). In several international studies, β -AB therapy of CHF patients was associated with reduced levels of haemoglobin (Hb) and development of new anaemia cases. Anaemia is known as an adverse prognostic factor in CHF. Aim. To study the effects of β -AB therapy on the anaemia clinical course among CHF patients. Material and methods. The study included 90 ambulatory patients with Functional Class (FC) II-IV CHF and anaemia. The participants were divided into 3 equally sized groups (n=30 per group) and treated with carvedilol, metoprolol, or nebivolol for 6 months. Results. By the end of the follow-up, baseline Hb levels increased in the nebivolol group (p=0,028), and were also significantly higher than in the other two groups. In the carvedilol group, the levels of haematocrit (Ht) and glomerular filtration rate (GFR) significantly decreased (p=0,017 and 0,06, respectively). In the metoprolol group, no substantial changes of laboratory parameters were observed. The maximal reduction in baseline CHF FC was registered in the patients receiving nebivolol (p=0,037). A significant improvement in myocardial contractility, based on the echocardiography data, was registered in the carvedilol and nebivolol groups. Conclusion. Nebivolol therapy was associated with a significantly more pronounced reduction in pro-BNP levels, compared to carvedilol or metoprolol treatment (p<0,001). The nebivolol group also demonstrated the most pronounced improvement in quality of life of CHF patients (p<0,001). These findings suggest that nebivolol could be recommended as a medication of choice in patients with CHF and anaemia.

The impact of new onset anaemia on morbidity and mortality in chronic heart failure: results from COMET

AIMS

Anaemia is a common comorbidity in chronic heart failure (CHF). The predictors of new onset anaemia (NOA) and its long-term prognostic value, particularly in patients treated with beta-blockers, are not known.

METHODS AND RESULTS

In COMET, 3029 patients with CHF in NYHA II-IV and EF <35% were randomized to carvedilol or metoprolol tartrate and were followed for an average of 58 months. Plasma haemoglobin (Hb) concentrations were measured at a central laboratory at randomization, at four monthly intervals for the first year and annually thereafter. According to WHO criteria, anaemia was defined when Hb measured <13 g/dL for men and <12 g/dL for women. We considered anaemia to be severe when Hb <11.5 g/dL for men and <10.5 g/dL for women. The baseline mean Hb was 14.2 +/- 1.5 g/dL (n = 2996) and 15.9% of patients had anaemia (males, 16.0%; females, 15.2%). At baseline, severe anaemia was found in 3.3% of patients (males, 3.6%; females, 2.0%). During the study, all-cause mortality (RR 1.47) death or hospitalization (RR 1.28), and heart failure hospitalization (RR 1.43, all P < 0.0001) were higher in anaemic when compared with non-anaemic patients. In patients without anaemia at baseline, at the end of the study, the cumulative frequency of NOA was 28.1% in males and 27.0% in females. NOA increased over time from 14.2% at year 1 to 27.5% at year 5. Predictors of NOA were: higher age, diuretic dose, creatinine (all P < 0.0001), higher serum potassium, lower serum sodium, body mass index, and use of aldosterone antagonists, carvedilol, and digitalis (all P < 0.03). Treatment with carvedilol (vs. metoprolol tartrate) was associated with a 24% increased risk to develop NOA (P = 0.0047), but not severe anaemia (P = 0.18). Patients with a Hb decrease of >3 g/dL (RR 3.37, P < 0.0001) or of 2.0-3.0 g/dL (RR 1.47, P = 0.011) from baseline had an increased subsequent mortality when compared with patients having Hb increases of 0-1.0 g/dL.

CONCLUSION

In stable ambulatory CHF patients, development of NOA is frequent and can be predicted by a set of clinical variables. Decreases in Hb over time relate to future increased morbidity and mortality.

Frizzled gene expression and development of tissue polarity in the Drosophila wing

Almost every cell in the Drosophila pupal wing forms a single, distally pointing cuticular hair. The function of the frizzled (fz) gene is essential for the elaboration of the normal wing hair pattern. In the absence of fz function hairs develop, but they display an abnormal polarity. We have examined the developmental expression of the fz gene at the RNA level via in situ hybridization and at the protein level via Western blotting. We have found that fz is expressed in all regions of the epidermis before, during, and after the fz cold sensitive period. We have also found that fz function is not required for normal fz expression. We have further found that mutations in several other tissue polarity genes do not noticeably alter the expression or the modification state of the Fz protein.

Beta-agonist-induced inhibitory-guanine-nucleotide-binding regulatory protein coupling to adenylate cyclase in mollusc Anodonta cygnea foot muscle sarcolemma

In the sarcolemma fraction of foot muscles of a fresh-water bivalve mollusc, Anodonta cygnea, a direct inhibitory, rather than stimulatory, effect of the beta-adrenergic agonist isoproterenol, at micromolar concentration, on cAMP level and adenylate cyclase activity, was revealed. It was blocked by beta- but not alpha-adrenergic antagonists. A single class of [3H]dihydroalprenolol-binding sites with binding properties of beta-adrenergic receptor was detected in mollusc sarcolemma. Potentiation of the inhibitory effect of isoproterenol on mollusc adenylate cyclase activity by GTP or guanosine 5'-[beta,gamma-imido]triphosphate at micromolar concentrations, and its elimination in the presence of guanosine 5'-[beta-thio]diphosphate, were shown. The pertussis-toxin-induced ADP-ribosylation of sarcolemma 40-kDa protein [immunochemically related in the C-terminal part to pertussis-toxin-sensitive guanine-nucleotide-binding regulatory protein (G-protein) alpha subunits of vertebrates], as well as the treatment of mollusc sarcolemma with antisera responsive to the C-terminus of vertebrate inhibitory G-protein (G(i)) alpha subunit led to elimination of the inhibitory effect of isoproterenol on adenylate cyclase activity. The results obtained suggest that beta-agonist-induced inhibition of adenylate cyclase in A. cygnea foot muscle may be realized via the beta-adrenoreceptor/G(i) signalling pathway.

Basal and drug-induced cAMP levels in cortical slices from the tottering mouse

Basal and drug-induced levels of cAMP were determined in cortical slices from mice which were homozygous for the tottering (tg/tg) gene defect as well as from co-isogenic controls (+/+). Basal levels of cAMP were 77 +/- 16% higher in tg/tg slices compared to the controls. This difference was abolished by exposure of the slices to propranolol, a beta-adrenergic receptor antagonist. Both isoproterenol and veratridine stimulated cAMP formation, but only small differences were observed in the cAMP levels in tg/tg and +/+ slices after this treatment. Of the veratridine-dependent increase in cAMP, approximately 40% was blocked by propranolol treatment of slices from both strains. The results suggest that a higher level of endogenous norepinephrine release in tottering mice contributes to an elevation of basal cAMP levels.

Beta-adrenergic receptor properties of a pulmonary alveolar type II cell preparation from the adult rat

The pulmonary alveolar type II cell synthesizes and secretes phosphatidylcholine (PC), a major component of surfactant, above basal level in response to beta-adrenergic stimulation. The investigation of the specific receptor which mediates these events was the topic of this study. Freshly isolated type II cells from adult rats were disrupted in a French pressure cell, and crude particulate fractions were recovered and used in assays for binding of the radioligand (-)-3-[125I]-iodocyanopindolol. The receptor had high affinity for beta-adrenergic agents, and specific binding to the receptor was saturable and reversible. The KD value obtained by kinetic means (19.6 pM) was in close agreement with that obtained by Scatchard (21.5 pM) and Hill (21.3 pM) analyses of steady-state binding data. The Scatchard correlation coefficients and Hill plot coefficients were close to 1, indicative of a single class of binding sites which displays no cooperativity. The specificity for catecholamine agonists and stereoselectivity observed were appropriate for a beta-adrenergic receptor. Use of selective drugs identified the presence of both beta 1- and beta 2-adrenergic receptor subtypes (1:3, respectively) on this cell type.

The binding of [3H]-tiotidine to homogenates of guinea-pig lung parenchyma

By use of a rapid filtration assay, the binding of [3H]-tiotidine to homogenates of guinea-pig lung parenchyma was found to be saturable and of a high affinity. Mean values for the KD and Bmax were calculated as 8.5 +/- 1.5 nM and 28 +/- 5 fmol mg-1 protein respectively. The association and dissociation rate constants for [3H]-tiotidine binding at 4 degrees C were calculated to be 0.81 +/- 0.06 microM min-1 and 0.063 +/- 0.005 min-1 respectively, yielding a kinetically derived KD of 7.8 nM. A wide range of H2-receptor agonist and antagonists displaced [3H]-tiotidine binding from lung parenchyma homogenates in a biphasic manner. Examination of the first phase of the displacement of [3H]-tiotidine yielded Ki values for the antagonists tested similar to those found in other binding studies using this ligand and similar to KB values calculated for the antagonists in pharmacological studies.

[Is the alpha adrenergic receptor density increased in intact thrombocytes in non-isometric trained athletes?]

Alpha-adrenoreceptors were determined as an equivalent to 3H-dihydroergocryptine (DHE) specifically bound on intact thrombocytes in five untrained volunteers (I), eight non-staticly trained sportsmen (II), and eight intensively staticly trained athletes (III). Bmax was 933 +/- 363 (I), 982 +/- 373 (II), and 1796 +/- 539 fmol DHE X 10(-9) thrombocytes (III). KD was 1.28 +/- 0.49 (I), 2.94 +/- 1.12 (II), and 3.58 +/- 1.07 nmol X l-1 (III). The number of binding sites per cell amounted to 561 +/- 202 (I), 589 +/- 224 (II), and 1078 +/- 323 (III). The thrombocytes of the staticly trained athletes showed a significantly higher number of binding sites and a slightly higher affinity (KD) than the other groups (p less than 0.01). However, a wide range of overlapping has to be considered. The biologic significance of these results and their transferability to other organs are open at present. It is the question whether an altered adrenoreceptor density may be one factor of a higher prevalence of hypertension in staticly trained athletes on which our research group has reported recently.

Criteria for receptor sites in binding studies

The study of binding is not an easy task especially because of the difficulty of interpreting the results in terms of binding on specific receptor sites. The problem is not new; what is new is the increasing amount of fanciful interpretation that such a technique has generated. The tendency to interpret anomalous or intriguing results in terms of new receptor subtypes seems to have reached its peak. The need to apply severe criteria becomes imperative before concluding that a binding site may be called a receptor site. Some pitfalls in binding studies will be discussed.

Adrenergic modulation of erythropoiesis: in vitro studies of colony-forming cells in normal and polycythaemic man

The effect of hormonal interactions on human erythroid colony growth has been studied using the beta adrenergic agonist, isoproterenol. The growth of colonies derived from both erythroid burst-forming cells (BFU-E) and erythroid colony-forming cells (CFU-E) was enhanced in the presence of isoproterenol. While isoproterenol was effective at all concentrations of erythropoietin (Ep) in cultures of marrow cells, an increase in BFU-E-derived colonies in peripheral blood cultures could be detected only at suboptimal levels of Ep concentrations. The isoproterenol effect was blocked by an agent with beta 2 receptor specificity (butoxamine), and L-isomeric configuration (L-propranolol). The stimulatory effect appeared to be mediated by a receptor different from that for Ep or for phytohaemagglutinin-stimulated leucocyte conditioned medium. Circulating BFU-E from eight patients with polycythaemia vera were also studied. Those colonies which grew in the absence of added Ep increased with isoproterenol; in cultures from normal subjects and in patients with secondary erythrocytosis, agonist stimulation was seen only in the presence of Ep. These studies provide evidence that the growth of both normal and neoplastic erythroid progenitors may be modulated by hormonal interactions.

Alcohol and the heart

Acute alcohol ingestion can lead to alterations of either mechanical function or electrophysiologic properties of the heart, whereas chronic consumption can lead to progressive cardiac dysfunction and congestive cardiomyopathy. On the other hand, alcohol appears to have a protective effect for coronary artery disease when consumed in low amounts, although prophylactic use of alcohol is not recommended.

Cyclic AMP in the regulation of exocytosis in the rat parotid gland. Evidence obtained with cholera toxin

The effects of cholera toxin on rat parotid gland function were determined in order to further characterize the relationship between cyclic AMP and exocytosis in this tissue. Cholera toxin induced the release of alpha-amylase from rat parotid minces in vitro. This release was accompanied by an activation of adenylate cyclase, elevated cyclic AMP levels, an elevated protein kinase activity ratio, and changes in the degree of phosphorylation of three endogenous phosphoproteins. Two of the phosphoproteins became more phosphorylated upon cholera toxin stimulation while the phosphorylation of the other decreased. The effects of cholera toxin on endogenous phosphoprotein labelling appeared to mimic those of the beta-adrenergic agonist isoproterenol but were of a smaller magnitude. These results are consistent with cyclic AMP functioning as a major mediator of exocytosis in this gland exerting its effects, at least in part, via activation of cyclic AMP dependent protein kinase. The mechanism by which an increased cyclic AMP level results in the decreased phosphorylation of an endogenous phosphoprotein is not known.

Recent advances in knowledge about beta-adrenergic receptors: application to clinical cardiology

The properties of beta-adrenergic receptors in the cardiovascular system have been studied in the past by two experimental approaches, which can be termed pharmacologic and biochemical. In the pharmacologic approach, the nature of a drug interaction with receptors is deduced from alterations in the physiologic properties of the tissue caused by administration of various concentrations of the drug. Many important concepts about beta-adrenergic receptors have come from such indirect pharmacologic studies. The biochemical approach directly assesses the interaction of drugs with beta-adrenergic receptors by studying the binding of radiolabeled antagonists and agonists with the receptor. This relatively new approach has provided a large amount of new information regarding the intrinsic properties of beta-adrenergic receptors and modification of these properties by physiologic stresses, administration of drugs and disease states. The biochemical approach has also been applied recently to the study of beta-adrenergic receptors in human beings. In the future, substantial clinically relevant new information regarding the nature of beta-adrenergic receptors in physiologic and pathologic conditions should result from application of a combination of the biochemical and physiologic approaches to studies in human beings.

Mapping of mammalian beta-adrenoreceptors by use of macromolecular alprenolol derivatives. A comparison with amphibian erythrocyte receptors

THe interaction of macromolecular alprenolol derivatives with beta-adrenoreceptors of rat heart, lung, and erythrocytes and frog erythrocytes has been studied. Macromolecular derivatives were prepared by covalently coupling alprenolol to dextrans containing a homologous series of spacer arms of various lengths. The affinity of these macromolecules for frog erythrocyte membranes increased with increasing length of spacer arm. In contrast, the affinity of these macromolecules for all mammalian membrane preparations was weak and insensitive to the length of the spacer arm. The inhibition of [3H]dihydroalprenolol binding to rat heart, lung, and erythrocyte membrane preparations by these macromolecular derivatives was more than 1000-fold less potent than inhibition by alprenolol. The results suggest different structural characteristics between mammalian and amphibian beta-adrenoreceptors; however, apparently only small differences between mammalian receptors could be distinguished with these probes.

Alterations in the properties of beta-adrenergic receptors of myocardial membranes in aging: impairments in agonist-receptor interactions and guanine nucleotide regulation accompany diminished catecholamine-responsiveness of adenylate cyclase

The effects of age on cardiac beta-adrenergic receptor linked adenylate cyclase system were studied using homogenates and membrane fractions of ventricular myocardium from young (3-4 months' old) and aged (24-25 months' old) rats. The number of beta-adrenergic receptor sites and the basal adenylate cyclase activities were essentially similar in young and aged hearts. On the other hand, striking age-associated alterations were seen in the properties of beta-receptors and adenylate cyclase in cardiac membranes. (A) The beta-receptor affinities for catecholamine agonists were reduced 10- to 20-fold in aged compared to young heart; the receptor affinity for antagonists were unaffected by age. (B) Guanine nucleotides caused a 9- to 17-fold reduction in beta-receptor affinity for isoproterenol in young heart; this guanine nucleotide-promoted reduction in receptor affinity for agonist was virtually absent in aged heart. (C) Guanine nucleotide-dependent stimulation of adenylate cyclase by isoproterenol was only 20-50% in aged heart compared to three-fold in young heart; beta-receptor-independent activation of the cyclase by guanine nucleotides and NaF were also reduced similarly in aged heart. These results demonstrate a marked age-associated deterioration in the functional integrity of beta-receptor linked adenylate cyclase system in aged heart. Further, the findings identify beta-receptor and guanine nucleotide regulatory protein as the components of the cyclase system affected in aging. It is suggested that the failure to form a "high-affinity" agonist-receptor complex, owing to the age-related decrement in receptor affinity for agonists, and the apparent inability of guanine nucleotide regulatory protein to effect appropriate molecular transitions at the level of both beta-receptor and the catalytic unit (i.e. the cyclase enzyme), contribute to the loss of catecholamine- and guanine nucleotide-responsiveness of adenylate cyclase in aged heart. This age-associated abnormality provides a biochemical basis for the well-recognized decline in adrenergic control of aging myocardium.

Myocardial adrenergic receptors and adenylate cyclase in the developing spontaneously hypertensive rat

Cardiac membrane preparations from developing spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats (0 to 125 days of age) were analyzed for the apparent numbers of alpha- and beta-adrenergic receptors and adenylate cyclase activities in an attempt to correlate biochemical changes with the reported functional changes occurring with the development of hypertension in the SHR. Although the apparent number of alpha- and beta-adrenergic receptors were similar in both strains of rats, isoproterenol-stimulated adenylate cyclase activities were significantly higher (P less than 0.05) in the prehypertensive SHRs when compared to WKY rats and declined to lower values as hypertension appeared. The percent stimulation produced by isoproterenol remained similar in cardiac membranes from normotensive WKY rats at all ages of development whereas this percent stimulation was 40% higher at birth in the SHRs and declined to approximately one half the original value by 100 days of age (P less than 0.05). The elevated adenylate cyclase activity observed during the prehypertensive state may contribute to the genesis of hypertension.

Down-regulation of the sodium pump following chronic exposure of HeLa cells and chick embryo heart cells to ouabain

1 HeLa cells and primary cultures of embryonic chick heart cells were grown in medium containing low concentrations of ouabain for 24 h. 2 Compared with normal cells, cells grown in ouabain have fewer free sodium pump sites, an increased intracellular sodium concentration and a decreased intracellular potassium concentration. The cells are able to maintain their intracellular ion contents because the remaining pump sites have an increased turnover rate. 3 When cells that have been chronically exposed to ouabain are returned to normal growth medium, the sodium pump site numbers increase; the recovery process begins within 6 to 8 h and is complete within 24 h. Recovery of pump site numbers is primarily dependent upon de novo protein synthesis since the protein synthesis inhibitor, cycloheximide, prevents recovery.

Micromolar calcium stimulates proteolysis and glutamate binding in rat brain synaptic membranes

Incubation of cortical synaptic membranes with low concentrations of calcium resulted in a decrease in the amount of a high-molecular-weight doublet protein and an increase in the sodium-independent binding of glutamate. Both effects were blocked by the thiol protease inhibitor leupeptin. These results suggest that calcium-induced proteolysis of membrane components regulates the number of glutamate receptors in neuronal membranes.

Neurotransmitter-receptor binding in various brain regions in ethanol-dependent rats

Since chronic ethanol administration has been demonstrated to induce a number of alterations in neurotransmitter utilization, the possibility was investigated that the receptors, on which these transmitters act, are altered because of a modified synaptic input. Male Sprague-Dawley rats were rendered physically-dependent on ethanol by the oral administration of 9-13 g/kg of ethanol each day over a 4 day period. The binding of radioligands specific for alpha-adrenergic, beta-adrenergic, dopaminergic, serotonergic, muscarinic cholinergic, and GABAergic receptors was assessed at various intervals after withdrawal in several areas of the brain. No alteration in receptor binding was observed at any point under the conditions studied. The data suggest that the signs of an ethanol withdrawal syndrome are not mediated through changes in the ability of neurotransmitters to interact with their receptors.

Optimal conditions for [3H]apomorphine binding and anomalous equilibrium binding of [3H]apomorphine and [3H]spiperone to rat striatal membranes: involvement of surface phenomena versus multiple binding sites

I. Binding of [3H] apomorphine to dopaminergic receptors in rat striatum was most reproducible and clearly detectable when incubations were run at 25 degrees C in Tris-HCl buffer, pH 7.5, containing 1 mM-EDTA and 0.01% ascorbic acid, using a washed total-membrane fraction. The receptor binding was stereospecifically inhibited by (+)-butaclamol, and dopamine agonists and antagonists showed high binding affinity for these sites. Unlabelled apomorphine inhibited an additional nonstereospecific binding site, which was unrelated to dopamine receptors. EDTA in the incubation mixture considerably lowered nonstereospecific [3H]apomorphine binding, apparently by preventing the complexation of the catechol moiety with metal ions which were demonstrated in membrane preparations. Stereospecific [3H]apomorphine binding was not detectable in the frontal cortex, whereas in the absence of EDTA much saturable nonstereospecific binding occurred. II. Kinetic patterns of stereospecific [3H]spiperone and [3H]apomorphine binding to rat striatal membranes and the inhibition patterns of a dopamine antagonist and an agonist were evaluated at different temperatures in high-ionic-strength Tris buffer with salts added and low-ionic-strength Tris buffer with EDTA. Apparent KD values of spiperone decreased with decreasing tissue concentrations. KD values of both spiperone and apomorphine were little influenced by temperature changes. Scatchard plots of the stereospecific binding changed from linear to curved; the amount of nonstereospecific binding of the 3H ligands varied considerably, but in opposite directions for spiperone and apomorphine in the different buffers. In various assay conditions, interactions between agonists, and between antagonists, appeared fully competitive, but agonist-antagonist interactions were of mixed type. The anomalous binding patterns are interpreted in terms of surface phenomena occurring upon reactions of a ligand with complex physicochemical properties and nonsolubilized sites on membranes suspended in a buffered aqueous solution. It is concluded that anomalous binding patterns are not necessarily an indication of binding to multiple sites or involvement of distinct receptors for high-affinity agonist and antagonist binding.

Preparation and spectroscopic characterization of molecular species of brain phosphatidylserines

This study describes the first preparation and spectroscopic characterization of naturally occurring phospholipids separated according to degree of unsaturation. Phosphatidylserines (PS) have been prepared from bovine brain and shown to be pure by extensive thin layer chromatographic analysis as well as by infrared spectroscopy and fatty acid analysis. The PS has been separated according to degree of unsaturation and prepared using AgNO3-impregnated silica gel H thin-layer chromatography. Fatty acid analysis of the two principal PS subfractions indicates that they are enriched in the molecular species 1-octadecanoyl-2-docosahexaenoyl-sn-glycero-3-phosphorylserine and 1-octadecanoyl-2-octadecenoyl-sn-glycero-3-phosphorylserine. The identity of the two PS subfractions was further verified by rechromatographing on several thin layer systems and by infrared spectroscopy. With the use of a 100 MHz Fourier transform nuclear magnetic resonance (NMR) spectrometer, the spectra of bovine whole brain, white matter, gray matter, monoenoic, and hexaenoic PS were obtained. Distinct proton resonances were assigned to double bond protons, protons adjacent to a double bond, and protons between two double bonds, using fatty acid methyl ester standards. The various PS preparations gave different intensities of the various proton resonances which correlated with differences in fatty acid composition. The method provides a convenient, non-destructive spectroscopic method for distinguishing monoenoic and polyunsaturated species of intact phospholipids. Electron spin resonance studies of nitroxide-labelled cholestane in sonicated PS vesicles showed greater probe motion as the unsaturation of the acyl chains was increased. The hexaenoic PS vesicles were more fluid than monoenoic PS vesicles at all temperatures in the range 10-55 degrees C. These results suggest that neuronal membranes are more fluid than myelin membranes as neuronal membranes contain more hexaenoic phospholipids.

Effects of beta adrenergic agents and prostaglandin E1 on erythroid colony (CFU-E) growth and cyclic AMP formation in Friend erythroleukemic cells

The formation of erythroid colonies from bone marrow and spleen cells infected with the polycythemic strain of the Friend virus (FV-P) was characterized in an in vitro methyl cellulose colony-forming system in response to prostaglandin E1 and the beta-2 adrenergic agonist, albuterol. Both drugs markedly inhibited the formation of CFU-E colonies of FV-P-infected bone marrow and spleen in the absence or presence of erythropoietin. The albuterol-mediated inhibition of CFU-E colonies (FV-P-infected) was selectively blocked by butoxamine, a beta-2 antagonist. Adenylate cyclase (AC) activity was also determined in FV-P spleen membrane preparations in response to albuterol and PGE1. Both agents stimulated enzyme activity, and butoxamine blocked the stimulation seen with albuterol. The ability of albuterol and PGE1 to stimulate AC activity in the FV-P-infected cells suggests that the effects of these agents on CFU-E formation may be mediated by specific beta-2 adrenergic and PG receptors through the adenylate cyclase-cyclic AMP system.

Cytoskeletal constraint of the beta-adrenergic receptor in frog erythrocyte membranes

A fluorescence receptor binding assay, based upon the high-affinity beta-adrenergic receptor antagonist propranolol, is utilized to probe the microenvironment of the antagonist-receptor complex in the frog (Rana catesbeiana) erythrocyte membrane. The technique of steady-state fluorescence depolarization is applied to the propranolol-receptor complex, allowing quantitation of the rotational relaxation time of the complex. It is found that the complex is dynamically constrained at 20 degrees C. However, in the temperature range 6-10 degrees C a sharp reversible release of constraint is observed. It is further demonstrated that the addition of drugs that are known to specifically disrupt the cytoskeleton (colchicine, vincristine, and vinblastine) causes a similar but irreversible release of constraint at 20 degrees C. Cytochalasin B has a much smaller influence on the rotational mobility of the propranolol-receptor complex than do the other drugs that disrupt the cytoskeleton. Amphotericin B is without effect on the rotational constraint of the complex. Binding of the antagonist [3H]dihydroalprenolol is not influenced by colchicine. A model is proposed which postulates that cytoskeletal elements are linked to the antagonist-receptor complex. Antagonist binding does not result in cytoskeletal release, whereas agonist binding is postulated to lead to dissociation of the agonist-receptor complex from the cytoskeleton, thereby activating adenylate cyclase.

Binding of [3H]cimetidine to rat brain tissue

Binding of [3H]cimetidine to rat brain tissue was investigated, and a saturable binding with dissociation constant 0.22 +/- 0.05 microM found. This binding is inhibited by a range of imidazole-derived histamine H2-receptor antagonists, but not by a number of non-imidazole H2-receptor antagonists. It is concluded that the [3H]cimetidine binding site in rat brain tissue that is labelled in these experiments is not the histamine H2-receptor.

N-Formylmethionyl peptide receptors on equine leukocytes initiate secretion but not chemotaxis

The chemotaxis of leukocytes appears to be initiated by the binding of chemotactic factors to the surface of these cells. N-Formylated peptides induce chemotaxis and lysosomal enzyme secretion of leukocytes; because these peptides are available in a purified radiolabeled form, they have been useful in the characterization of receptors for chemotactic factors. Equine polymorphonuclear leukocytes secrete lysosomal enzymes but do not exhibit chemotaxis in respone to the N-formylated peptides, even though they have a high-affinity cell surface receptor for these agents. The specificity of the equine receptor resembles the specificity of the receptor on chemotactically responsive leukocytes from other species. Equine polymorphonuclear leukocytes may thus be an excellent model for the study of the events that lead to a biological response following receptor occupancy.

Development of specific receptors for N-formylated chemotactic peptides in a human monocyte cell line stimulated with lymphokines

A human monocyte-like cell line, U937, when grown in continuous culture, does not secrete lysosomal enzymes or migrate towards chemotactic factors. When the cells are stimulated by lymphokines, however, they develop the ability both to migrate directionally and to secrete enzymes in response to several types of chemoattractants. The development, by stimulated cells, of chemotactic and secretory responses to one class of chemoattractants, the N- formylated peptides, is accompanied by the appearance on the cells of specific binding sites for these substances. Using tritiated N-formyl- methionyl-leueyl-phenylalanine (fMet-Leu-[(3)H]Phe) as a ligand, it was determined that unstimulated U937 cells possess no detectable binding sites. However, after stimulation with lymphocyte culture supernates for 24, 48, and 72 h, they developed 4,505 (+/-) 1,138, 22,150(+/-) 4,030, and 37,200 (+/-) 8,000 sites/cell, respectively. The dissociation constants for the interaction of fMet-Leu-[SH]Phe with the binding sites were approximately the same regardless of stimulation time and ranged between 15 and 30 nM. The binding of fMet-Leu-[(3)H]Phe by stimulated U937 cells was rapid and readily reversed by the addition of a large excess of unlabeled peptide. The affinity of a series of N-formylated peptides for binding to U937 cells exactly reflected the potency of the peptides in inducing lysosomal enzyme secretion and chemotaxis. The availability of a continuous human monocytic cell line that can be induced to express receptors for N-formylated peptides will provide a useful tool not only for the characterization of such receptors but also for the delineation of regulatory mechanisms involved in cellular differentiation and the chemotactic response.

Relationship between the (--)-[3H]-dihydroalprenolol binding to beta-adrenoceptors and transmembrane 86Rb efflux of the BC3H1 nonfusing muscle cell line

1 We have studied the binding properties of the beta-adrenoceptor antagonist [3H]-dihydroalprenolol ([3H]-DHA) on a membrane preparation of the non-fusing muscle cells BC3H1. 2 [3H]-DHA appears to bind to two classes of sites. The first site has a high affinity (KD = 0.53 nM) and a low capcity (Bmax = 58 fmol/mg of protein). The second site has a low affinity (KD = 110 nM) and a high capacity (Bmax = 1100 fmol/mg of protein). 3 The pharmacological properties of the high affinity low capacity site correspond to the known properties of the beta 2-adrenoceptors since the agonists inhibit [3H]-DHA binding following the series isoprenaline greater than adrenaline greater than noradrenaline greater than phenylephrine and the antagonists following the series alprenolol congruent to propranolol greater than butoxamine greater than practolol greater than phentolamine. 4 The binding properties of the beta-adrenoceptors were correlated with the effect of beta-adrenoceptor agonists and antagonists on 86Rb efflux rate from BC3H1 Cells. 5 There is very good correlation between the dissociation constants obtained by inhibition of [3H]-DHA binding by the antagonists alprenolol and propranolol, and the inhibition constants calculated from their antagonism of the 86Rb efflux rate stimulation by adrenaline. The ratio of the dissociation constants obtained by inhibition of [3H]-DHA binding by agonists and their EC50, calculated from 86Rb efflux curves, is higher than 1. This high KD/EC50 ratio indicates a high coupling efficiency between receptor occupancy by agonists and the biological effect measured.

Macromolecular beta-adrenergic antagonists discriminating between receptor and antibody

The beta-adrenergic antagonist, alprenolol, was attached in an irreversible manner to macromolecular dextran via side arms that differed in length. The ability of these macromolecules to bind to the beta-adrenergic receptor of frog erythrocytes and to catecholamine-binding antibodies raised against partially purified receptors was studied. Compared to the parent drug the potency of binding of macromolecular alprenolol to the receptor decreased about 1/10, 1/600, and 1/8000 when the length of the arm separating alprenolol from the dextran moiety was 13, 8, and 4 atoms, respectively. In contrast, the binding potencies of the parent drug and of all its macromolecular derivatives for the antibody were within the same order of magnitude. Thus, conversion of a drug to a macromolecular form may not only sustain its binding activity but may also lead in a higher selectivity. The macromolecular derivatives described here may be suitable probes for investigation of the location and of the molecular properties of the binding sites for beta-adrenergic drugs.

Modification of dopamine receptor-mediated processes after chronic ethanol intoxication: a possible mechanism

Animals undergoing withdrawal from chronic ethanol treatment displayed significantly impaired function of dopaminergic systems in the CNS. Autonomic and behavioral response to dopaminergic agonists were reduced, as was the stimulation by dopamine of dopamine-sensitive adenylate cyclase from the striatal region of brain. In addition, the ability of neuroleptics to stimulate tryosine hydroxylase activity in the subcortex was diminished. These findings suggested a decreased sensitivity of dopaminergic receptors during ethanol withdrawal, and in time course of appearance and disappearance, the decreased sensitivity appeared to parallel ethanol withdrawal hyper-excitability. Moreover, the responsiveness of dopamine-sensitive adenylate cyclase could be restored by in vitro exposure to physiologically attainable concentrations of ethanol, suggesting that this system had become dependent on the presence of ethanol for normal function. The mechanism of the decreased sensitivity, in particular for the adenylate cyclase, but perhaps also for other dopamine receptor-mediated processesx, may be inefficient coupling between receptor and enzyme, as a result of changes in neuronal membrane structure produced by chronic exposure to ethanol and withdrawal.