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M G Caron

Publications and source records attributed to M G Caron.

At least 343 records · Page 19Linked to original sources
PubMed1985

Homologous desensitization of the beta-adrenergic receptor. Functional integrity of the desensitized receptor from mammalian lung.

Previous work has demonstrated that injection of rats with isoproterenol is rapidly (10 min) followed by the development of a homologous form of desensitization of the beta-agonist-coupled adenylate cyclase in lung membranes. Half the receptor pool becomes sequestered in a light membrane fraction while the other half remains in the plasma membranes but becomes functionally uncoupled. In the present work we sought to assess whether "local sequestration" of the functionally intact receptor away from the effector adenylate cyclase in the plasma membrane contributes to the uncoupling of the beta-adrenergic receptor observed in the plasma membranes. We tested the functionality of the desensitized beta-adrenergic receptor in three different ways. We reconstituted the affinity chromatography purified control and "desensitized" receptors with pure Ns from human erythrocytes and assessed the ability to induce GTPase activity in Ns. Both control and desensitized beta-adrenergic receptors stimulate similar levels of GTPase activity in Ns (852 +/- 38 versus 738 +/- 49 fmol of Pi released/30 min (p greater than 0.05, n = 4). To further assess the relative ability of control and desensitized beta-adrenergic receptors to couple to another source of Ns we fused reconstituted beta-adrenergic receptors to Xenopus laevis erythrocytes, which contain Ns and adenylate cyclase but essentially no beta-adrenergic receptors. The functional interactions of control and desensitized beta-adrenergic receptor with the adenylate cyclase system of the acceptor cells was assessed by measuring the beta-agonist-stimulated adenylate cyclase activity and the agonist-induced formation of the high affinity state of the beta-adrenergic receptor (RH). Again both control and desensitized beta-adrenergic receptors appeared to interact with Ns to the same extent. To test if a local sequestration of the beta-adrenergic receptor away from Ns within the plasma membrane might contribute to the uncoupling of the beta-adrenergic receptors during desensitization, plasma membranes from control and desensitized lungs were treated with the fusogen polyethylene glycol to disrupt any compartmentalization of protein components within the plasma membrane. After polyethylene glycol treatment the previously uncoupled beta-adrenergic receptors could be recoupled to Ns as assessed by the formation of RH in agonist competition curves. These data suggest that in marked contrast to the heterologous type of desensitization, homologous desensitization may involve a local sequestration of a functionally intact beta-adrenergic receptor away from the adenylate cyclase effector system.

Adenylyl Cyclases↗
PubMed1984

Photoaffinity labeling of beta-adrenergic receptors in mammalian tissues.

Photoaffinity labeling of beta 1- and beta 2-adrenergic receptors in plasma membranes from various mammalian tissues has been been performed utilizing the recently developed beta-adrenergic antagonist probe [125I]para-azidobenzylcarazolol. Tissues studied and their proportions of beta 1 and beta 2 receptors were: rat lung (18% beta 1, 82% beta 2), rabbit lung (72% beta 1, 28% beta 2), guinea pig lung (15% beta 1, 85% beta 2), dog lung (20% beta 1, 80% beta 2) and rabbit skeletal muscle (10% beta 1, 90% beta 2). As assessed by autoradiograms of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, two to three specifically protected bands of Mr 62,000-65,000, 50,000-55,000 and 38,000-42,000 were observed in each tissue system. In each case, beta-adrenergic agonists and antagonists protected against photolabeling with appropriate beta 1 and beta 2 selectivity. Thus, in rat lung the beta 2 selective antagonist ICI-118,551 was more potent in blocking incorporation than the beta 1 selective antagonist betaxolol, whereas in rat, dog and guinea pig lung and rabbit skeletal muscle epinephrine was more potent than norepinephrine in blocking labeling, indicating a beta 2 specificity in these tissues. Conversely, in rabbit lung membranes, norepinephrine was approximately equipotent with epinephrine in blocking photoincorporation, indicating a beta 1 selectivity. In some systems protease inhibitors, especially those specific for metalloproteases (EDTA, EGTA), markedly diminished the amount of the smaller Mr peptides. For example, in rat lung the ratio of Mr 62,000:47,000:36,000 peptides changed from 30:40:30 to 60:35:5 in the presence of inhibitors. These results demonstrate the applicability of using [125I]para-azidobenzylcarazolol to covalently label mammalian beta-adrenergic receptors and suggest that mammalian beta 1 and beta 2 receptor binding sites primarily reside on peptides of Mr 62,000-65,000 and that smaller ligand binding fragments may arise by proteolysis.

Affinity Labels↗
PubMed1984

A novel radioiodinated high affinity ligand for the D2-dopamine receptor. Characterization of its binding in bovine anterior pituitary membranes.

A novel high affinity dopaminergic ligand, N-(p-aminophenethyl)spiroperidol, has been synthesized and radioiodinated to a specific radioactivity of 2175 Ci/mmol. Binding of this ligand to bovine anterior pituitary membranes is: rapid (40-60 min to equilibrium at 25 degrees C) and reversible (t1/2 = 1 h at 25 degrees C); saturable and of high affinity (KD approximately 20 pM) and displays a typical D2-dopaminergic specificity. The ligand, which identifies the same number of receptor sites as other tritiated antagonist ligands, can be used in different tissues and preparations to delineate the characteristics of the D2 receptor. Thus, this high affinity, high specific radioactivity ligand (N-(p-amino-m-[125I]iodophenethyl)spiroperidol) represents a tool which until now had not been available for the characterization of the D2-dopamine receptor.

Animals↗
PubMed1984

The mammalian beta 2-adrenergic receptor: purification and characterization.

The beta 2-adrenergic receptors from hamster, guinea pig, and rat lungs have been solubilized with digitonin and purified by sequential Sepharose-alprenolol affinity and high-performance steric-exclusion liquid chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography of iodinated purified receptor preparations reveal a peptide with an apparent Mr of 64 000 in all three systems that coincides with the peptide labeled by the specific beta-adrenergic photoaffinity probe (p-azido-m-[125I]iodobenzyl)carazolol. A single polypeptide was observed in all three systems, suggesting that lower molecular weight peptides identified previously by affinity labeling or purification in mammalian systems may represent proteolyzed forms of the receptor. Purification of the beta-adrenergic receptor has also been assessed by silver staining, iodinated lectin binding, and measurement of the specific activity (approximately 15 000 pmol of [3H]dihydroalprenolol bound/mg of protein). Overall yields approximate 10% of the initial crude particulate binding, with 1-3 pmol of purified receptor obtained/g of tissue. The purified receptor preparations bind agonist and antagonist ligands with the expected beta 2-adrenergic specificity and stereoselectivity. Peptide mapping and lectin binding studies of the hamster, guinea pig, and rat lung beta 2-adrenergic receptors reveal significant similarities suggestive of evolutionary homology.

Animals↗
PubMed1984

The mammalian beta 2-adrenergic receptor: reconstitution of functional interactions between pure receptor and pure stimulatory nucleotide binding protein of the adenylate cyclase system.

Pure beta-adrenergic receptors (beta-AR) isolated from guinea pig lung and pure guanine nucleotide binding regulatory protein (NS) of adenylate cyclase isolated from human erythrocytes have been inserted into phospholipid vesicles, resulting in the functional coupling of these two components. The reconstitution of receptor and NS interactions results in the establishment of a guanine nucleotide sensitive state of the receptor that binds agonists with high affinity. Competition curves of isoproterenol for labeled antagonist binding to vesicles containing both beta-AR and NS are biphasic and reveal two affinity states, one of high (approximately 2 nM) and the other of low affinity (approximately 300 nM). In the presence of guanine nucleotides, the competition curves become monophasic and are shifted to a single low-affinity state for the agonist similar to the situation observed in membrane preparations. In addition, the interactions of the receptor and NS lead to the induction of a GTPase activity in NS. The GTPase activity can be stimulated by beta-adrenergic agonists such as isoproterenol (2-5-fold) and is completely blocked by antagonists such as alprenolol in a stereoselective manner. The established hormone responsive activity retains the beta 2-adrenergic specificity conferred by the pure receptor, and similar extents of stimulation (up to 4-fold) are observed with pure receptor from frog erythrocytes, indicating a similar efficiency of coupling between receptors from different species and NS.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
PubMed1984

Reconstitution of a hormone-sensitive adenylate cyclase system. The pure beta-adrenergic receptor and guanine nucleotide regulatory protein confer hormone responsiveness on the resolved catalytic unit.

A hormone responsive adenylate cyclase has been reconstituted in phosphatidylcholine vesicles from its isolated protein components. The proteins used were the affinity chromatography purified (500-2000-fold) or pure Mr = 64,000 beta-adrenergic receptors (beta AR) isolated from hamster and guinea pig lung membranes, the pure heterotrimeric (Mr: alpha = 42,000; beta = 35,000; gamma approximately equal to 5,000) guanine nucleotide regulatory protein (Ns) isolated from human erythrocyte membranes; and the catalytic unit of the adenylate cyclase (C) solubilized from bovine brain caudate nucleus and resolved from beta AR and Ns by gel filtration. Adenylate cyclase activity in vesicles containing C alone was stimulated by forskolin but not by guanine nucleotides or by the beta-adrenergic agonist isoproterenol. Reconstitution of Ns and C interactions in the lipid vesicles resulted in guanine nucleotide but not beta-adrenergic agonist sensitivity. When beta AR was inserted together with Ns and C into lipid vesicles, the catalytic unit became responsive to beta-adrenergic agonists as well and this stimulation was blocked in a stereoselective manner by the beta-adrenergic antagonist alprenolol. Regulation of adenylate cyclase activity in the reconstituted system by beta-adrenergic agonists, guanine nucleotides, and Mg2+ showed properties similar to those observed in native membranes. The interactions of the various protein components in the reconstituted system were also monitored by GTPase activity. Such activity was observed to occur primarily as a result of receptor-Ns interactions. The results described in this report document the feasibility of studying hormone-responsive adenylate cyclase in a totally reconstituted system which retains the major regulatory properties of the enzyme in its native membrane-bound environment.

Adenylyl Cyclases↗
PubMed1984

Direct demonstration of impaired functionality of a purified desensitized beta-adrenergic receptor in a reconstituted system.

Long-term exposure of various cell types to beta-adrenergic agonists such as isoproterenol leads to an attenuated responsiveness ("desensitization") of the adenylate cyclase system to further challenge with these agonists. The turkey erythrocyte model system was used earlier to show that a covalent modification of the receptor (phosphorylation) is associated with this process. The functionality of the "desensitized" beta-adrenergic receptor was assessed by implanting purified beta-adrenergic receptor preparations from control and desensitized turkey erythrocytes into phospholipid mixtures and then fusing them with receptor-deficient cells (Xenopus laevis erythrocytes). Desensitized beta-adrenergic receptors showed a 40 to 50 percent reduction in their ability to couple to the heterologous adenylate cyclase system, comparable to the reduction in their functionality observed in their original membrane environment. These results demonstrate the utility of recently developed receptor reconstitution techniques for assessing the functionality of purified receptors and show a direct link between a covalent modification of a membrane-bound receptor and its impaired functionality in a reconstituted system.

Adenylyl Cyclases↗
PubMed1984

Desensitization of turkey erythrocyte adenylate cyclase. Beta-adrenergic receptor phosphorylation is correlated with attenuation of adenylate cyclase activity.

Preincubation of turkey erythrocytes with beta-adrenergic agonists leads to an attenuation of the responsiveness of adenylate cyclase to subsequent hormonal stimulation. Recently, our laboratory has shown (Stadel, J. M., Nambi, P., Shorr, R. G. L., Sawyer, D. D., Caron, M. G., and Lefkowitz, R. J. (1983) Proc. Natl. Acad. Sci. U. S. A. 80, 3173-3177) using 32Pi incorporation that phosphorylation of the beta-adrenergic receptor accompanies this desensitization process. We now report that, as determined from intracellular [gamma-32P] ATP specific activity measurements, this phosphorylation reaction occurs in a stoichiometric fashion. Under basal conditions there exists 0.75 +/- 0.1 mol of phosphate per mol of receptor whereas under maximally desensitized conditions this ratio increases to 2.34 +/- 0.13 mol/mol. This phosphorylation of the receptor is dose-dependent with respect to isoproterenol and exhibits a dose-response curve coincidental with that for isoproterenol-induced desensitization of adenylate cyclase. The time courses for receptor phosphorylation and adenylate cyclase desensitization are identical. In addition, the rate of resensitization of adenylate cyclase activity is comparable to the rate of return of the phosphate/receptor stoichiometries to control levels. Both the phosphorylation and desensitization reactions are pharmacologically specific as indicated by the high degree of stereoselectivity, rank order of catecholamines, and blockade by the specific beta-adrenergic antagonist, propranolol. Incubation of turkey erythrocytes with cAMP and cAMP analogs maximally activates cAMP-dependent protein kinase but only partially mimics isoproterenol in promoting phosphorylation of the receptor in concordance with their partial effects in inducing desensitization. Conversely, activators or inhibitors of Ca2+/calmodulin kinase or protein kinase C do not affect the isoproterenol-induced desensitization. These results indicate that desensitization of turkey erythrocyte adenylate cyclase is highly correlated with phosphorylation of the beta-adrenergic receptor and that these events are mediated, at least partially, by cAMP.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1984

Mammalian beta-adrenergic receptors. Distinct glycoprotein populations containing high mannose or complex type carbohydrate chains.

Mammalian beta-adrenergic receptor binding peptides can be visualized by covalently labeling them with the photoaffinity reagent p-azido-m-[125I]iodobenzylcarazolol followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. The receptor peptides migrate as broad bands of Mr approximately equal to 62,000. In the present study, we examined the carbohydrate composition of the mammalian beta receptor through the use of specific exo- and endoglycosidases and lectin affinity chromatography. Treatment of p-azido-m-[125I]iodobenzylcarazolol-labeled beta2-adrenergic receptors from hamster lung or rat erythrocyte with the exoglycosidases neuraminidase and alpha-mannosidase provided evidence for the existence of both high mannose and complex type carbohydrate chains on beta 2-adrenergic receptors. The nonadditivity of the effect of sequential treatments with these enzymes suggested discrete populations of beta-adrenergic receptors containing either complex or high mannose type chains. Deglycosylation of receptor with endoglycosidase F results in a single labeled polypeptide at Mr = 49,000 for both systems. The same two populations of the beta receptors (high mannose or complex type chain) could also be fractionated by lectin affinity chromatography of solubilized p-azido-m-[125I]iodobenzylcarazolol-labeled receptors. The high mannose-containing receptors could be absorbed to and specifically eluted from concanavalin A-agarose. Those containing complex type carbohydrates could be adsorbed to and eluted from wheat germ agglutinin-agarose. Taken together, these data suggest that mammalian beta-adrenergic receptors contain both complex and high mannose type carbohydrate chains and that microheterogeneity of these chains likely explains the broad band pattern typically obtained on sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Affinity Labels↗
PubMed1984

Identification of the subunit-binding site of alpha 2-adrenergic receptors using [3H]phenoxybenzamine.

alpha 2-Adrenergic receptors are members of an important class of membrane-bound receptors which appear to mediate physiologic responses by decreasing the activity of the regulatory enzyme adenylate cyclase. This report describes the first direct indentification of the subunit-binding site of alpha 2-adrenergic receptors. alpha 2-Adrenergic receptors from human platelets were solubilized with 1% digitonin and were purified approximately 600-fold by repetitive affinity chromatography. In saturation and competition binding studies using [3H]yohimbine the original alpha 2-adrenergic characteristics were retained by the partially purified receptor, i.e. the following potency series (based on Ki values) was obtained: phentolamine approximately equal to yohimbine much greater than prazosin and (-)epinephrine greater than (+)epinephrine. Phenoxybenzamine was found to have a Ki for the partially purified alpha 2-adrenergic receptor of 108 nM. As judged by the loss of specific [3H]yohimbine binding, phenoxybenzamine (a known alkylating agent) was found to bind irreversibly to the partially purified alpha 2-adrenergic receptor. Using [3H]phenoxybenzamine, covalent labeling of proteins in the partially purified receptor preparation was obtained. Following sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography, a specifically labeled peptide with a relative molecular mass of 61,000 was visualized. Irreversible labeling of this peptide by [3H]phenoxybenzamine could be prevented with either phentolamine or (-)epinephrine, but not with prazosin or (+)epinephrine, suggesting that this peptide of Mr = 61,000 represents the major subunit binding site of the human platelet alpha 2-adrenergic receptor.

Binding, Competitive↗
PubMed1984

Dopamine receptor of the porcine anterior pituitary gland. Solubilization and characterization.

In the anterior pituitary gland, dopamine controls the release of prolactin from the mammotrophs. The dopamine receptors in the porcine gland have been shown to exist in two different affinity states of equal proportion, one bearing high affinity for agonists and labeled by 3H-agonist-ligands and the other displaying low affinity for agonists. Both forms of the receptor can be labeled by 3H-antagonist-ligands. Dopamine receptors from porcine anterior pituitary membranes can be solubilized with retention of their ability to interact with specific dopaminergic ligands. Treatment of membrane preparations with 1% digitonin resulted in the solubilization of 20-25% of the specific binding sites labeled by [3H] spiroperidol with a specific activity of about 100 fmoles/mg. The receptor was a glycoprotein as assessed by the interaction of these binding sites with agarose-immobilized lectin. [3H]Spiroperidol binding in solubilized preparations was saturable, of high affinity (KD = 570 pM), and to a single class of stereoselective binding sites. Agonist competition for [3H]spiroperidol binding indicated that, whereas the solubilized receptor retained its dopaminergic specificity, the high-affinity interactions of the receptor with agonists present in membranes and sensitive to guanine nucleotides were lost in solubilized preparations. Thus, the KD values calculated from the agonist competition curves for [3H]spiroperidol corresponded to the agonist affinities for the low-affinity state of the receptor documented in membranes. However, high-affinity agonist binding and its sensitivity to guanine nucleotides were preserved when the membrane-bound receptor was prelabeled with the agonist [3H]N-n-propylnorapomorphine prior to solubilization. These results suggest that a component that confers agonist high-affinity binding and guanine nucleotide responsiveness to the receptor is lost during solubilization unless a stable complex is formed with the agonist prelabeled receptor prior to solubilization.

Animals↗
PubMed1984

Photoaffinity labeling of turkey erythrocyte beta-adrenergic receptors: degradation of the Mr = 49,000 protein explains apparent heterogeneity.

The potent photoaffinity probe [125I]p-azidobenzylcarazolol was used to identify beta-adrenergic receptors from turkey erythrocytes. Two peptides were specifically labeled with apparent Mr = 39,000 and 49,000 on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The ratio of labeling of these peptides was found to be dependent on the method of tissue preparation. Thus, the Mr = 39,000/Mr = 49,000 ratio was 1:2 when labeling was done on intact cells, 1:1 for labeling of crude membranes, and 4:1 for purified membrane preparations. Moreover, incubation of intact cells or either membrane preparation at 37 degrees C led to a diminution of the Mr = 49,000 labeled peptide which was associated with a stoichiometric increase in the Mr = 39,000 form of the receptor. These results suggest that the turkey erythrocyte beta-adrenergic receptor is a protein of Mr = 49,000 and that the commonly observed Mr = 39,000 peptide is derived from this protein.

Affinity Labels↗
PubMed1984

Photoaffinity labeling of mammalian alpha 1-adrenergic receptors. Identification of the ligand binding subunit with a high affinity radioiodinated probe.

We have synthesized and characterized a novel high affinity radioiodinated alpha 1-adrenergic receptor photoaffinity probe, 4-amino-6,7-dimethoxy-2-[4-[5-(4-azido - 3 - [125I]iodophenyl) pentanoyl] - 1 - piperazinyl] quinazoline. In the absence of light, this ligand binds with high affinity (KD = 130 pM) in a reversible and saturable manner to sites in rat hepatic plasma membranes. The binding is stereoselective and competitively inhibited by adrenergic agonists and antagonists with an alpha 1-adrenergic specificity. Upon photolysis, this ligand incorporates irreversibly into plasma membranes prepared from several mammalian tissues including rat liver, rat, guinea pig, and rabbit spleen, rabbit lung, and rabbit aorta vascular smooth muscle cells, also with typical alpha 1-adrenergic specificity. Autoradiograms of such membrane samples subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveal a major specifically labeled polypeptide at Mr = 78,000-85,000, depending on the tissue used, in addition to some lower molecular weight peptides. Protease inhibitors, in particular EDTA, a metalloprotease inhibitor, dramatically increases the predominance of the Mr = 78,000-85,000 polypeptide while attenuating the labeling of the lower molecular weight bands. This new high affinity radioiodinated photoaffinity probe should be of great value for the molecular characterization of the alpha 1-adrenergic receptor.

Affinity Labels↗
PubMed1984

Dopaminergic inhibition of adenylate cyclase correlates with high affinity agonist binding to anterior pituitary D2 dopamine receptors.

Dopamine (DA) and the dopaminergic agonists n-propylnorapomorphine (NPA), 2-amino-6,7-dihydroxytetrahydronaphthalene (ADTN) and apomorphine (APO) inhibit forskolin-stimulated adenylate cyclase activity in a dose-dependent fashion by more than 40% in membrane preparations of the porcine anterior pituitary gland. These agonists exhibit apparent dissociation constants that follow an expected dopaminergic order of potency (NPA greater than ADTN greater than or equal to APO greater than DA). The inhibition is dependent on guanine nucleotides and is reversible by dopaminergic antagonists (spiroperidol greater than (+)-butaclamol much greater than (-)-butaclamol). The potencies of these agonists in inhibiting forskolin-stimulated adenylate cyclase activity correlate with the agonist dissociation constants (KH) for binding to the high affinity receptor state (RH) in porcine anterior pituitary membranes (De Lean et al., Mol. Pharmacol. 1982, 22, 290-297) and the EC50 for inhibition of prolactin release from rat anterior pituitary cells in culture (Caron et al., J. Biol. Chem. 1978, 253, 2244-2253). Furthermore, the intrinsic activities of dopamine and the other agonists for inhibition of forskolin-stimulated adenylate cyclase are similar and correlate well with the ability of these agents to induce a comparable proportion (50%) of the receptor in a high affinity state. Together these data provide additional support for the physiological relevance of the high affinity agonist binding state of the D2 receptor in mediating the decrease in prolactin secretion via attenuation of adenylate cyclase.

Adenylyl Cyclase Inhibitors↗
PubMed1984

Development of an affinity ligand for purification of alpha 2-adrenoceptors from human platelet membranes.

Human platelets contain alpha 2-adrenoceptors which are negatively coupled to the enzyme adenylate cyclase. In order to better understand the interaction of this subtype of alpha receptor with this key enzyme, we have initiated a program to isolate and characterize the alpha 2-adrenoceptor. This report describes the synthesis and biological characterization of a series of molecules that were prepared as affinity ligands for this purpose. The best of these is 9-(allyloxy)-6-chloro-3-methyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SK&F 101253). This compound is an alpha 2-adrenoceptor antagonist, which was obtained by synthetic modification of 6-chloro-3-methyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SK&F 86466), a novel antagonist with high affinity for the alpha 2-receptor.

Affinity Labels↗
PubMed1984

Skeletal muscle beta-adrenergic receptors: variations due to fiber type and training.

To determine the relationship between oxidative capacity and characteristics of beta-adrenergic receptors (beta AR) in skeletal muscle, selected biochemical variables were quantitated in particulate preparations from soleus and gastrocnemius muscle from rats subjected to 10 wk of treadmill running and from three control groups: free-fed, sedentary controls; food-restricted, pair-weighted controls; and animals trained by swimming. Beta AR density and isoproterenol-stimulated adenylate cyclase activity were considerably greater in the slow-twitch oxidative soleus muscle than in the mixed fiber type gastrocnemius in animals from each group (P less than 0.005). Succinic dehydrogenase (SDH) activity of gastrocnemius was increased 23-42% (P less than 0.05) in runners over each of the control groups, concommitantly with a 15-27% increase (P less than 0.05) in beta AR density (Bmax for binding of 125I-cyanopindolol). In 24 animals from all four treatment groups, there was a significant correlation between SDH activity and beta AR density (r = 0.68; P less than 0.001). We conclude that BAR density correlates positively with oxidative capacity in skeletal muscle, but further studies are required to determine the physiological importance of these differences.

Adenylyl Cyclases↗