Beta 2-adrenoceptor up-regulation in relation to cAMP production in human lymphocytes after physical exercise

The effect of isotonic bicycle exercise on beta 2-adrenoceptors and cAMP production in lymphocytes was studied. The origin of the newly exposed receptors was studied by measuring radioligand binding in the presence of hydrophylic or lipophylic 'cold' ligands. During exercise beta 2-adrenoceptor density increased from 1207 +/- 144 to 1776 +/- 152 sites/cell (56 +/- 14%). Isoprenaline induced an increase in cAMP synthesis, which was 68 +/- 15% higher than those values measured before the test. Forskolin did not induce a higher increase in cAMP production after exercise. The increase in receptor density seems not to be due to a transfer of internalized receptors to the membrane surface. We conclude that physical exercise induces an up-regulation of beta 2-adrenoceptors on lymphocytes and that these adrenoceptors are functional.

Cardiac beta-adrenoceptor binding characteristics with age following adrenal demedullation

1. The role of adrenal medullary catecholamines in the regulation of cardiac function becomes more important when adrenergic neural influences in the heart are decreased. Since adrenergic nervous input to the heart decreases with age, it would be expected that catecholamine influence on cardiac neuroeffector junction would increase. 2. Fischer-344 rats of 6-, 12- and 24-months were adrenal demedullated or sham-operated and the animals were killed at the end of two weeks. beta-Adrenoceptors were studied in the membrane preparations from the ventricles of rat hearts. [125I]-iodopindolol was used as the radioligand. The density of beta-receptors (Bmax), dissociation constant (KD) and the ratio of cardiac beta-adrenoceptor subtypes were studied. The relative percentages of beta-receptor subtypes were determined by use of ICI 89,406 (beta 1-selective antagonist) and ICI 118,551 (beta 2-selective antagonist). 3. In 24-month-old animals which were adrenal demedullated, hydrocortisone replacement was employed for one week; the animals were killed one week later. 4. The data indicate that there was a diminution of the Bmax following adrenal demedullation at all ages but that the ratios of beta 1: beta 2-adrenoceptors remain the same as in the controls (67:33). The effect of adrenal medullary catecholamines on cardiac beta-receptor binding characteristics did not seem to be influenced by age.

Rabbit alveolar beta-adrenergic receptors increase with gestational age

Pulmonary beta-adrenergic receptors, which mediate the actions of endogenous catecholamines, increase before birth, an important step in pulmonary maturation. This increase, which occurs primarily in the alveoli, may be hastened by corticosteroids. However, because the lung is composed of more than 40 cell types, we asked whether the normal distribution of beta-adrenergic receptors changes with gestational age in a way that seems physiologically relevant. We compared lungs from fetal rabbits at 26 and 31 days' gestation with lungs from adult rabbits by autoradiography with 125iodocyanopindolol, a beta-adrenergic antagonist. While the total silver grain concentration increased during gestation, the greatest proportional increase occurred in the alveoli. We conclude that pulmonary beta-adrenergic receptor concentration increases during gestation and that this increase is most dramatic for alveoli. This pattern is consistent with that previously observed after treatment of fetal rabbits in utero with corticosteroids.

Receptor modification in the brains of spontaneously hypertensive and Wistar-Kyoto rats: regionally specific and selective increase in cerebellar beta 2-adrenoceptors

Quantitative in vitro autoradiography was used to study beta-adrenergic and benzodiazepine receptor density in discrete regions from sagittal brain sections of 20 week old hypertensive (SHR) and normotensive (WKY) rats. The density of beta-adrenoceptors was increased by 68% in the granule cell layer of the cerebellum of the SHR without a change in receptor affinity; this increase was specific for receptors of the beta 2-subtype. On the other hand, benzodiazepine receptor density was unchanged in the cerebella of SHR. These results indicate that brain beta-adrenoceptors are differentially modulated by the hypertensive state which may be either a cause or a consequence of alterations in adrenergic nervous system activity found in the SHR.

Beta-adrenergic receptor sensitivity in subjects practicing transcendental meditation

Several studies suggest that behavioral techniques such as meditation and relaxation may be associated with reduced end organ adrenergic receptor sensitivity. Thus far the evidence supporting this hypothesis has been indirect. We present preliminary findings showing reduced beta-adrenergic receptor sensitivity in a group of subjects practicing Transcendental Meditation. The meditation group (N = 10), compared to controls (N = 10), had a lower percentage of functional lymphocyte beta-adrenergic receptors (p = 0.009), but showed no difference in total receptor number or plasma catecholamines. There were no differences between the groups in Type A behavior, the Type A components, exercise, or family history of hypertension. The results provide some support for studies postulating that meditation is associated with reduced sympathetic adrenergic receptor sensitivity, and provide encouragement for the efficacy of receptor measurement in psychophysiology research.

Protein kinase A and/or C inhibitors potentiate isoproterenol-induced cyclic AMP accumulation in intact human lymphocytes

The objective of the present study was to investigate the roles of protein kinase A and/or C in agonist-induced beta adrenoceptor activation in intact human lymphocytes. LYmphocytes from healthy subjects were incubated with isoproterenol and phosphodiesterase inhibitor (IBMX, 1.0 mM) after 20 minutes of preincubation with (or without) various compounds possessing protein kinase A and/or C inhibitory activities. These compounds included the relatively selective protein kinase C (PK-C) inhibitors (W-7, calmidazolium, polymyxin B, neomycin, tamoxifen and clomiphene), purified protein inhibitors of protein kinase A (PK-A) (obtained synthetically, or purified from bovine hearts and porcine hearts) and the two compounds (H-7, H-9), which have been found to inhibit both PK-A and PK-C. The results showed that all PK-C inhibitors alone decreased cellular basal cAMP levels while inhibitors of PK-A as well as both H-7 and H-9 increased basal cAMP levels in a dose dependent manner at certain concentrations. All inhibitors studied potentiated isoproterenol-induced cAMP accumulation. The protein kinase A and C inhibitor, H-7, also potentiated PGE1 (but not forskolin)-induced cAMP accumulation. In contrast, the protein kinase C activator, PMA, inhibited isoproterenol- and PGE1- (but not forskolin) induced cAMP accumulation. These data suggest that the potentiating effects of PK-A and/or C inhibitors may be related to the inhibition of PK-A and/or PK-C, both of which have been shown to be involved in beta 2 adrenoceptor desensitization and phosphorylation.

Beta adrenergic binding sites in the human eye: an autoradiographic study

Beta adrenergic binding sites were localized and characterized in the human eye by means of "in vitro" autoradiography, using [125I] (-) iodocyanopindolol (125ICYP) as radioligand. Binding sites were visualized by apposition of isotope sensitive film to slide mounted eye sections. Receptor sites were present in the extraocular muscles, in the conjunctiva, in the epithelium and endothelium of the cornea, in the trabeculum and in the ciliary muscle. They were also present in the lens epithelium and in the retina. The pigmented ocular structures were heavily labelled but the binding was nonspecific. Characterization of these binding sites was achieved by testing the ability of selective adrenergic compounds to displace 125ICYP binding. These studies suggested that the majority of adrenergic binding sites in nonpigmented structures of human eye were of a beta2 type.

The relationship between the hypokalaemic response to adrenaline, beta-adrenoceptors, and Na(+)-K+ pumps in skeletal and cardiac muscle membranes in the rabbit

The hypokalaemic response to adrenaline and the involvement of beta-adrenoceptors and Na(+)-K+ pumps were investigated in control rabbits and animals chronically pretreated with adrenaline. The hypokalaemic response to acute intravenous infusion of adrenaline was significantly reduced when rabbits were chronically pretreated with adrenaline for 10 days. Chronic pretreatment of rabbits with adrenaline significantly reduced the densities for [125I]cyanopindolol and [3H]ouabain binding sites in skeletal muscle and heart. Furthermore, there was a strong positive correlation (r = 0.97, p less than 0.001) between the Bmax for ICYP and [3H]ouabain, in the rabbit heart. Ouabain-sensitive 86Rb uptake and the activity of 3-O-methylfluorescein phosphate phosphatase were used to assess the function of the Na(+)-K+ pump in skeletal and cardiac muscle. There was no significant difference in these functional indices of the Na(+)-K+ pump between the control and adrenaline-pretreated animals, in skeletal or cardiac muscle. Thus, downregulation of the [3H]ouabain binding sites did not appear to be accompanied by reduced function of the Na(+)-K+ pump. Additional investigations are required to confirm further the dissociation between the function of the pump and the ouabain binding sites.

Distribution of beta 1- and beta 2-adrenoceptors in mouse trachea and lung: a quantitative autoradiographic study

1. Binding and quantitative autoradiography were used to detect [125I]-iodocyanopindolol (I-CYP) associated with beta 1- and beta 2-adrenoceptors in mouse tracheal epithelium and airway smooth muscle as well as in lung parenchymal tissue. 2. Specific I-CYP binding to slide-mounted tissue sections of both trachea and parenchyma was of high affinity (KD = 49.0 pM, n = 3, trachea; KD = 118.9 pM, n = 3, parenchyma) and saturable, involving single populations of non-interacting binding sites (Hill coefficient nH = 1.00 +/- 0.02, trachea; nH = 0.99 +/- 0.03, parenchyma). 3. Direct measurement of tissue radioactivity also showed that specific I-CYP binding was competitively inhibited in the presence of the beta-adrenoceptor antagonists (-)-propranolol (non-selective), CGP 20712A (beta 1-selective) and ICI 118,551 (beta 2-selective). Analysis of the competition binding curves for the two selective antagonists revealed mixed populations of beta 1- and beta 2-adrenoceptors in the approximate proportions 33% and 67% respectively in mouse trachea and 28% and 72% respectively in mouse lung parenchyma. 4. Densities of autoradiographic grains derived from specific I-CYP binding to alveolar wall tissue and to tracheal epithelium and airway smooth muscle were quantified by a computer-assisted image analysis system, which allowed the construction of competition binding curves in the presence of the selective beta-adrenoceptor antagonists CGP 20712A and ICI 118,551. Analysis of these data demonstrated that in alveolar wall, beta 1- and beta 2-adrenoceptors co-existed in the proportions 18% and 82%, respectively. 5. Quantitative autoradiographic analyses also showed that beta 1- and beta 2-adrenoceptors were differentially distributed in tracheal epithelium and airway smooth muscle. The beta 2-adrenoceptor subtype accounted for 71% of all beta-adrenoceptors in epithelium. Conversely, beta l-adrenoceptors which mediate relaxant responses of mouse trachea to beta,-adrenoceptor agonists (Henry & Goldie, 1990), accounted for 69% of all beta-adrenoceptors in the airway smooth muscle.

Laminar distributions of muscarinic acetylcholine, serotonin, GABA and opioid receptors in human posterior cingulate cortex

Experimental animal studies have demonstrated a number of receptor localizations on specific cortical afferents and neurons. The present study of human posterior cingulate cortex evaluates the laminar distributions of particular receptors and their likely association with components of the neuropil. Coverslip autoradiographic and single grain counting techniques were used followed by heterogeneity analysis in which the layer of peak binding and an index of heterogeneity were determined for each ligand. The index was calculated by determining specific binding by layer as a percentage of binding in all layers. The differences from an absolutely homogeneous distribution, i.e. 11.1% for each of nine layers, were subtracted and the absolute laminar differences summed to form the index. High indices of over 15 reflected heterogeneous binding patterns in neocortex. The binding of ligands for muscarinic acetylcholine, serotonin, opioid, GABA and beta adrenoceptors was evaluated. Pirenzepine binding peaked in layer II of area 23a but was extremely homogeneous with an index of heterogeneity of 8.9. In contrast, oxotremorine-M binding had a peak in layer IIIc and an index of 16.4, while AF-DX 116 binding peaked in layer IIIa-b and had an index of 30.6. Of the ligands for serotonin uptake and receptor binding paroxetine binding was evenly distributed in layers I-III and had a low index of heterogeneity of 9.8. Ketanserin binding was also homogeneous and, since it had an index of 8.9, this pattern was virtually the same as that for paroxetine. In contrast, serotonin and 8-hydroxy-2-(di-n-propylamino)tetralin binding peaked in layer II and had very high indices of 20.8 and 50.3, respectively, suggesting only a limited association with that of the paroxetine distribution. Finally, there were three layers which contained peaks in binding for ligands for opioid, GABA and beta adrenoceptors. Firstly, layer Ia had peak dynorphin-A binding, the latter of which had an index of 22.6. Secondly, Tyr-D-Ala-Gly-MePhe-Gly-ol and 2-D-penicillamine-5-D-penicillamine-enkephalin binding peaked in layer II and had indices of 8.6 and 17.4, respectively. Thirdly, muscimol and (-)-cyanopindolol binding peaked in layer IIIa-b and had indices of 29.6 and 11.1, respectively. When viewed in the context of experimental animal studies, it is likely that heterogeneities in oxotremorine-M and paroxetine binding are associated with the termination of the thalamic and raphe nuclei, respectively. While serotonin 2 receptors are co-distributed with serotonin uptake sites, serotonin 1A receptors have a significant mismatch with these sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of beta adrenergic receptor binding characteristics and coupling to adenylate cyclase in rat pulmonary artery versus aorta

In an effort to define the mechanisms regulating pulmonary vasodilatation and explain the greater in vitro response to iso-proterenol in the pulmonary artery (PA) vs. aorta (AO), we compared beta adrenergic receptor binding characteristics and coupling to adenylate cyclase in PA and AO obtained from adult male rats. Beta adrenergic receptor binding characteristics and affinity for agonists were determined with [125I]-iodocyanopindolol. Agonist displacement studies were characteristic of a beta-2 adrenergic receptor subtype. Receptor density (44.7 +/- 7.3 vs. 39.6 +/- 0.8 fmol/mg of protein means +/- S.E.M., PA vs. AO) and the dissociation constant for the radioligand (10.3 +/- 2.6 vs. 13.4 +/- 3.5 pM) were similar in the two arteries. However, affinity for l-isoproterenol was greater (the inhibition constant was lower) in PA compared to AO (0.08 +/- 0.03 vs. 1.20 +/- 0.18 microM, P less than .05), as was affinity for l-epinephrine (0.89 +/- 0.20 vs. 3.87 +/- 0.62 microM, P less than .05). Affinity was similar for l-norepinephrine (18.93 +/- 3.63 vs. 13.49 +/- 3.12 microM). Base-line cyclic AMP (cAMP) content, basal adenylate cyclase activity and adenylate cyclase activity stimulated by GTP, isoproterenol plus GTP and forskolin were measured by radioimmunoassay for cAMP. Base-line cAMP content was greater in PA than in AO (513.5 +/- 46.9 vs. 125.5 +/- 19.1 pmol of cAMP per mg of protein, P less than .001), as was basal adenylate cyclase activity (10.8 +/- 1.2 vs. 5.7 +/- 1.3 pmol of cAMP per mg of protein per min, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Differential regulation of human cardiac beta-adrenergic and muscarinic receptors by chronic beta-adrenoceptor antagonist treatment

In patients undergoing coronary artery bypass grafting chronic beta 1-adrenoceptor antagonist treatment increased right atrial beta 1-adrenoceptor number, did not affect beta 2-adrenoceptor number and decreased muscarinic M2-receptor number. Concomitantly, the M2-receptor-mediated negative inotropic effect of carbachol was reduced, while the beta 1-adrenoceptor-mediated positive inotropic effect of noradrenaline was not altered. The beta 2- adrenoceptor mediated positive inotropic effect of procaterol, however, was markedly enhanced. We conclude that chronic beta 1-adrenoceptor antagonist treatment increases beta 1-adrenoceptor number, sensitizes beta 2-adrenoceptor function and desensitizes M2-receptor function in the human heart.

Catecholamines increase lymphocyte beta 2-adrenergic receptors via a beta 2-adrenergic, spleen-dependent process

We investigated the mechanisms underlying the increase in mononuclear leukocyte (MNL) beta 2-adrenergic receptor (AR) number and responsiveness after acute infusion of catecholamines. Infusion of isoproterenol and epinephrine, but not of norepinephrine, acutely increased MNL beta-AR density, and this was blocked by the beta 2-selective antagonist ICI 118,551 but not by the beta 1-selective antagonist bisoprolol, suggesting a beta 2-AR-mediated effect. Infusion of isoproterenol but not of norepinephrine also induced a lymphocytosis, with an increase in the number of circulating suppressor/cytolytic T (Ts/c)- and natural killer (NK)-cells but a decrease in helper T (Th)-cells, leading to a decreased Th-Ts/c-cell ratio. beta-AR density was higher in Ts/c-cells than in Th-cells. After isoproterenol infusion, beta-AR density was elevated in all lymphocyte subsets but not in monocytes or platelets, suggesting a lymphocyte-specific phenomenon. Infusion of isoproterenol in splenectomized patients did not alter lymphocyte subset composition and only slightly increased beta 2-AR density. In healthy subjects lymphocyte proliferation in response to various mitogens was attenuated after infusion of isoproterenol but not of norepinephrine; this effect was abolished in splenectomized patients. We conclude that the elevated MNL beta-AR density after acute exposure to beta-adrenergic agonists is caused by a release of lymphocyte subsets from the spleen into the circulation and/or by an exchange of lymphocyte subsets between the spleen and the circulation, whereby freshly released splenic lymphocytes appear to carry more beta-AR than those found in the circulation. This appears to impair immune responsiveness in a dual manner, by decreasing the Th-/Ts/c-cell ratio and by rendering lymphocytes more sensitive to the antiproliferative effects of catecholamines via a higher beta-AR density.

Viral pneumonia attenuates adenylate cyclase but not beta-adrenergic receptors in murine lung

Respiratory infections provoke increased airway reactivity in both asthmatic and otherwise healthy subjects in part through impaired beta-adrenergic relaxation of bronchial and tracheal muscle. The precise mechanism remains obscure, but some studies report a decrease in the number of beta-adrenergic receptors. The present study was designed to assess the effect of viral respiratory infection with influenza A on lung beta-adrenergic receptors and adenylate cyclase activation in mice under two separate protocols. First, to determine whether changes are due to a local or systemic effect, we compared mice with influenza infections limited to the upper respiratory tract to mice with infection of the total respiratory tract. Four days after upper respiratory tract infection there were no changes in either isoproterenol- or NaF-stimulated adenylate cyclase activity. In contrast, there was an 82% decrease in isoproterenol- and a 25% decrease in NaF-stimulated adenylate cyclase activity on the fourth day after total respiratory tract infection. There were no changes in beta-adrenergic receptors or receptor coupling to adenylate cyclase with either type of infection. Our second protocol compared acutely infected mice to postrecovery mice. Twelve days after infection the virus was no longer present in the lungs, and adenylate cyclase activity was restored to normal. These data suggest that viral respiratory infection may impair airway function through attenuation of receptor and postreceptor activation of adenylate cyclase activity.

Serotonin depletion unmasks serotonergic component of [3H]dihydroalprenolol binding in rat brain

Selective lesions of serotonin neurons or inhibition of serotonin synthesis results in an increase in the number of [3H]dihydroalprenolol binding sites in several areas of rat brain. Previously, this increase in binding sites was interpreted as an increase in beta-adrenergic receptors. However, the lesion-induced increase in [3H]dihydroalprenolol is not accompanied by an increase in isoproterenol- or norepinephrine-stimulated cyclic AMP production. The increased binding of [3H]dihydroalprenolol is blocked by the addition of serotonin but not by the addition of norepinephrine or dopamine to the assays. Furthermore, the addition of metergoline, a serotonin antagonist, also blocked the increase in lesioned tissues. Thus, the lesion-induced increase in [3H]dihydroalprenolol binding appears to represent an increase in serotonergic binding sites. Among drugs with some selectivity for serotonin-1 receptor subtypes, trifluoromethylphenylpiperazine and RU-24929 were as effective as serotonin in blocking lesion-induced increases in [3H]dihydroalprenolol binding. However, 8-hydroxy-N,N-dipropyl-2-aminotetralin (8-OH-DPAT), spiperone, and mesulergine were either much less effective than serotonin or completely ineffective. Radioligand binding to serotonin-1A and serotonin-1B sites with [3H]8-OH-DPAT and 125I-cyanopindolol, respectively, after lesions of serotonin axons or depletion of serotonin was not increased, despite a marked increase in [3H]dihydroalprenolol binding in the same tissues. When tissues from control rats or rats with serotonin lesions were preincubated at 37 degrees for 10 min to remove endogenous serotonin bound to receptors, the binding of [3H]dihydroalprenolol in controls was increased to the level seen in lesioned tissues. Thus, [3H]dihydroalprenolol binds primarily to beta-adrenergic receptors in control membranes that are not preincubated; however, either preincubation of control tissues or serotonin depletion unmasks a serotonin-1 receptor subtype to which [3H]dihydroalprenolol binds in addition to the beta-adrenergic receptor.

Regulation of beta 1- and beta 2-adrenoceptors following chronic treatment with beta-adrenoceptor antagonists

The effect of chronic pretreatment of guinea pigs with various beta-adrenoceptor antagonists on the binding characteristics of the radioligand 125I-cyanopindolol (ICYP) and responsiveness of adenylate cyclase to isoprenaline in the gastrocnemius muscle (beta 2-adrenoceptors) and the left ventricle (beta 1-adrenoceptors) were compared. Pretreatment of guinea pigs with propranolol or ICI 118,551 for one week significantly increased the density of the beta 2-adrenoceptors in the gastrocnemius muscle. Atenolol pretreatment for one week did not affect the density of the receptors. Pretreatment of the animals with pindolol for one week reduced the density of beta 2-adrenoceptors in skeletal muscle. In the left ventricle pretreatment of the guinea pigs with any of the antagonists did not alter either the density or the KD of beta 1-adrenoceptors. The responsiveness of adenylate cyclase to isoprenaline (10(-4) M) in the left ventricle or skeletal muscle was not affected when the guinea pigs were pretreated with propranolol. Pretreatment of the guinea pigs with reserpine (0.5 mg.kg-1) intraperitoneally for one week, to deplete catecholamines did not affect beta-adrenoceptor density or KD in the left ventricle or skeletal muscle. We conclude that the regulation of beta-adrenoceptors by the antagonist may not be caused by the prevention of the access of endogenous agonists to beta-adrenoceptors and it is dependent on the selectivity of the antagonist and on the susceptibility of the receptors to regulation.

Altered adrenergic response and specificity of the receptors in rat ascites hepatoma AH130

Adenylate cyclase activation through adrenergic receptors in rat ascites hepatoma (AH) 130 cells in response to adrenergic drugs was studied, and receptor binding and displacement were compared with those of normal rat hepatocytes. Epinephrine (Epi) and norepinephrine (NE) activated AH130 adenylate cyclase about half as much as isoproterenol (IPN) but equaled IPN after treatment with the alpha-antagonist phentolamine or islet-activating protein (IAP). The three catecholamines in hepatocytes were similar regardless of phentolamine or IAP. These catecholamines activated adenylate cyclase in order of IPN greater than NE greater than Epi in AH130 cells but IPN greater than Epi greater than NE in hepatocytes. We then used the alpha 1-selective ligand [3H]prazosin, the alpha 2-selective ligand [3H]clonidine, and the beta-ligand [125I]iodocyanopindolol [( 125I]ICYP), and found that AH130 cells had few prazosin-binding sites, about eight times as many clonidine-binding sites with high affinity, and many more ICYP-binding sites than in hepatocytes. The dissociation constant (Ki) of the beta 1-selective drug metoprolol by Hofstee plots for AH130 cells was lower than that for hepatocytes. The inhibition of specific ICYP binding by the beta 2-selective agonist salbutamol for AH130 cells gave only one Ki value which was much higher than both high and low Ki values of the drug for hepatocytes. These findings indicate that the alpha- and beta-adrenergic receptors in hepatocytes are predominantly alpha 1-type and beta 2-type, but that those in AH130 cells are predominantly alpha 2-type and beta 1-type, and the low adrenergic response of AH130 cells is due to the dominant appearance of alpha 2-adrenergic receptors, linked with the inhibitory guanine-nucleotide binding regulatory protein, instead of alpha 1-adrenergic receptors, and beta 1-adrenergic receptors with low affinity for the hormone.

Persistent desensitization of the heart to the inotropic action of isoproterenol by adenosine

Isolated guinea pig hearts were perfused with Krebs buffer in the absence or presence of 10 microM adenosine for 60 to 120 min followed by a 15 min washout with adenosine-free buffer. The effects of isoproterenol on left ventricular dP/dt and heart rate were then determined. Perfusion with adenosine for a minimum of 90 min followed by washout resulted in a 40% depression of the dose-response curve of left ventricular dP/dt to isoproterenol. This depressed inotropic responsiveness persisted for at least 1 hr after cessation of adenosine perfusion. The heart rate response to isoproterenol was unaffected. Also, adenosine perfusion had no effect on ouabain inotropism. Measurement of adenosine in coronary effluent and in ventricular tissue by radioimmunoassay verified that no residual elevated adenosine remained following perfusion and washout. Moreover, isoproterenol-induced release of adenosine into the coronary effluent did not differ between control and adenosine-treated hearts. Addition of 100 microM theophylline, an adenosine receptor antagonist, to the adenosine containing buffer during perfusion prevented the depressed response to isoproterenol. In membrane fractions prepared from ventricles, beta receptors were assessed by (-) [125] iodocyanopindolol binding and neither the density of these receptors nor their affinity for agonists or antagonists was altered by adenosine perfusion. However, activation of adenylate cyclase by isoproterenol (10 microm) was significantly depressed in membranes from adenosine perfused hearts. These findings are consistent with a receptor mediated action of adenosine to produce persistent depression of catecholamine inotropism. Such an effect may be important in heart failure where myocardial levels of adenosine are elevated and circulating levels of catecholamines are high.

Autoradiographic localization of beta-adrenoceptors in asthmatic human lung

The autoradiographic distribution and density of beta-adrenoceptors in human non-diseased and asthmatic bronchi were investigated using [125I]iodocyanopindolol (I-CYP). Analysis of the effects of the beta-adrenoceptor antagonists on I-CYP binding demonstrated that betaxolol (20 nM, beta 1-selective) had no significant effect on specific grain density in either nonasthmatic or asthmatic human bronchus, whereas ICI-118551 (20 nM, beta 2-selective) inhibited I-CYP binding by 85 +/- 9% and 89 +/- 3%, respectively. Thus, homogeneous populations of beta 2-adrenoceptors existed in bronchi from both sources. Large populations of beta-adrenoceptors were localized to the bronchial epithelium, submucosal glands, and airway smooth muscle. Asthmatic bronchial tissue featured epithelial damage with exfoliated cells associated with luminal mucus plugs. A thickened basement membrane and airway smooth muscle hyperplasia were also evident. High levels of specific I-CYP binding were also detected over asthmatic bronchial smooth muscle, as assessed by autoradiography and quantitation of specific grain densities. Isoproterenol and fenoterol were 10- and 13-fold less potent, respectively, in bronchi from asthmatic lung than in those from nonasthmatic lung. However, this attenuated responsiveness to beta-adrenoceptor agonists was not caused by reduced beta-adrenoceptor density in asthmatic airways. A defect may exist in the coupling between beta-adrenoceptors and postreceptor mechanisms in severely asthmatic lung.

[Beta-adrenoreceptors in the muscular tissue of Anodonta cygnea]

The beta-adrenoceptors in the muscular tissue of Anodonta cygnea have been studied for the first time with the use of antagonist [125I] iodocyanopindolol. The tissue membrane had only one class of binding sites with Kd 2.9 +/- 0.02 pM and the maximal number of binding sites (Bmax) 110 +/- 2.4 fmoles/mg of protein. The potency of beta-agonists and antagonists for displacing [125I] iodocyanopindolol for its beta-AR complexes was the following: isoproterenol greater than adrenaline greater than noradrenaline-propranolol greater than serotonin much greater than dopamine greater than phentolamine. The GTP negative regulation of beta-AR affinity has been found. The data obtained show that the beta-AR are functionally coupled with GTP-binding protein which were similar to GTP-proteins of vertebrates.

Effect of aging on properties and function of beta-adrenoceptors in rat lung

beta-Adrenoceptor density and ligand affinity, basal adenylate cyclase activity and cAMP synthesis upon stimulation with forskolin, fluoride, guanine nucleotides (GTP or guanylyl imidodiphosphate (GppNHp) or isoproterenol in the presence of the nucleotides were studied in membranes prepared from lungs of young (aged 2-3 months) and of old (aged 24-25 months) male Wistar rats. There was a significant (P less than 0.05, 21%) increase in beta-receptor density and a significant (P less than 0.05, 38%) decrease in the percentage of high-affinity binding sites for isoproterenol. Both basal adenylate cyclase activity and that after stimulation with guanine nucleotides or isoproterenol in the presence of nucleotides were unaltered with age. Forskolin stimulation of cAMP synthesis was significantly reduced (by 24%, P less than 0.05) in tissues from older animals. It is suggested that the age-dependent changes in properties of beta-receptors in rat lungs are compensatory, in order to ensure equal cAMP production for equal agonist stimulation.

Localization of beta-adrenergic receptors in A431 cells in situ. Effect of chronic exposure to agonist

The status of beta-adrenergic receptors was investigated in A431 cells exposed to chronic stimulation by the beta-adrenergic agonist, (-)-isoproterenol. Specific binding of beta-adrenergic antagonist (-)-[125I]iodocyanopindolol declined to 60-80% below control values within 12 h of agonist treatment. This decline in ligand binding was also observed in high-speed membrane fractions prepared from agonist-treated cells. Immunoblots probed with anti-receptor antibodies revealed both that beta-adrenergic receptors from untreated and treated cells migrated as 65,000-Mr peptides and that the cellular complement of receptor was unchanged. Indirect immunofluorescence localization of beta-adrenergic receptors was comparable in control (untreated) cells and cells challenged with (-)-isoproterenol for 1, 12, or 24 h. Thus receptor complement, migration on SDS/polyacrylamide-gel electrophoresis, and localization in situ are largely unaffected by agonist stimulation. Receptor binding of antagonist radioligands, in contrast, is markedly down-regulated in cells stimulated chronically with beta-adrenergic agonists. These data argue in favour of agonist-induced alteration(s) in the conformation of the receptor that preclude radioligand binding rather than agonist-induced receptor sequestration and/or degradation.

Indirect immunofluorescence localization of beta-adrenergic receptors and G-proteins in human A431 cells

Polyclonal antibodies directed against (i) rodent lung beta 2-adrenergic receptor, (ii) a synthetic fragment of an extracellular domain of the receptor, and (iii) human placenta G-protein beta-subunits, were used to localize these antigens in situ in intact and permeabilized human epidermoid carcinoma A431 cells. Antibodies directed against beta 2-adrenergic receptors showed a punctate immunofluorescence staining throughout the cell surface of fixed intact cells. Punctate staining was also observed in clones of Chinese hamster ovary cells transfected with an expression vector harbouring the gene for the hamster beta 2-adrenergic receptor. The immunofluorescence observed with anti-receptor antibodies paralleled the level of receptor expression. In contrast, the beta-subunits common to G-proteins were not stained in fixed intact cells, presumably reflecting their intracellular localization. In detergent-permeabilized fixed cells, strong punctate staining of G beta-subunits was observed throughout the cytoplasm. This is the first indirect immunofluorescence localization of beta-adrenergic receptors and G-proteins. Punctate immunofluorescence staining suggests that both antigens are distributed in clusters.

Characterization, localization and pharmacological profile of a high-affinity [3H]lidocaine binding site

Electrophysiological findings support the existence of voltage-dependent, sodium channel-associated receptors for class I antiarrhythmics. We have tried to identify such receptors with tritiated lidocaine. High-affinity binding sites were discovered in heart and brain membranes, but liver and kidney particulate fractions had the highest density of sites. The dissociation constants were 75 nM in bovine heart and 29 nM in guinea-pig liver membranes. Binding was reversible (t 1/2: 102 s at 2 degrees C), optimal at pH 9-10 and was only partly destroyed by heat treatment. Subcellular fractionation experiments excluded a plasmalemmal association of the lidocaine site in heart. The competition profile of 16 antiarrhythmics indicated chemical comparability of the sites in heart and liver. These data greatly challenge the applicability of labeled lidocaine as sodium channel probe. The pharmacological significance of the site described here remains to be clarified.

5-HT1B and 5-HT2 serotonin binding sites in cultured Wistar-Kyoto rat aortic smooth muscle cells

We studied [3H]serotonin [( 3H]5-HT) binding on cultured arterial smooth muscle cells from rat aorta. We found a high and low affinity binding site. Binding to the higher affinity site could be displaced by drugs in an order corresponding most closely with the 5-HT1B subtype, and high affinity [125I]iodo-cyanopindolol binding was also found. We found evidence for a 5-HT2 subtype using [3H]ketanserin binding, with similar results whether specific binding was determined using unlabelled ketanserin, methysergide or mianserin.