Studies on the hepatic alpha 1-adrenergic receptor. Modulation of guanine nucleotide effects by calcium, temperature, and age.

Lynch, Christopher J.; Charest, R; Blackmore, Peter F.; Exton, John H.

doi:10.1016/s0021-9258(18)89635-1

Cited by 79 publications

(11 citation statements)

References 30 publications

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“…When incubations were performed in the presence of 0.1 mM Gpp(NH)p, the resultant curves now indicated exclusive interaction of (-)-epinephrine with low-affinity sites (Figure 1). This is in agreement with previous reports (El Refai et al, 1979;Goodhardt et al, 1982;Lynch et al, 1985) that guanine nucleotides convert a,-adrenergic receptors to a single state of low affinity for agonists.…”

Section: Resultssupporting

confidence: 94%

“…The virtual identity of the dissociation constants at 4 °C, and for the small percentage of high-affinity sites identified at 37 °C, can be reconciled with a two-state model of the receptor for agonists, where the receptor is "locked" in the high-affinity configuration when incubations are performed at the low temperature. This locking of the high-affinity configuration in the cold is further demonstrated by the inability of Gpp(NH)p to decrease the affinity for agonists when studies are performed at 4 °C, in agreement with the findings reported by Lynch et al (1985).…”

Section: Resultssupporting

confidence: 91%

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Agonist-induced isomerization of the .alpha.1-adrenergic receptor: kinetic analysis using broken-cell and solubilized preparations

Schwarz¹,

Lanier²,

Sena³

et al. 1986

Biochemistry

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The affinity of agonists but not antagonists at hepatic membrane alpha 1-adrenergic receptors is temperature dependent; a 100-fold higher affinity is observed at 4 degrees C than at 37 degrees C. The relationship between these two agonist affinity states was investigated by using a strategy that allows the kinetics of this transition to be examined under equilibrium conditions. When competition assays are performed at 37 degrees C for varying intervals and the reaction mixture is then rapidly cooled by freezing, allowed to thaw, and further equilibrated at 4 degrees C, a rapid and progressive decrease (t1/2 of 1-2 min) in agonist affinity occurs, the extent of which is directly related to the incubation time at 37 degrees C. This decrease in agonist affinity is sustained as long as agonist is present but can be reversed by its subsequent removal. In contrast, no change in affinity is seen in identical experiments when antagonists are employed as the competing ligand. High-affinity binding of agonists is also demonstrated in short-term nonequilibrium experiments, indicating that the low-temperature incubations do not induce, but rather stabilize, a receptor conformation of high affinity for agonists. These findings suggest that the predominantly low-affinity binding of agonists to alpha 1-adrenergic receptors demonstrated in equilibrium studies at physiological temperatures may be the result of a ligand-driven decrease in affinity. Since the transition in receptor affinity for agonists occurs not only in broken-cell preparations but also after detergent solubilization of the membrane receptor, it most likely is due to an agonist-induced change in the conformation of the receptor protein per se.(ABSTRACT TRUNCATED AT 250 WORDS)

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Section: Resultssupporting

confidence: 94%

Section: Resultssupporting

confidence: 91%

Agonist-induced isomerization of the .alpha.1-adrenergic receptor: kinetic analysis using broken-cell and solubilized preparations

Schwarz¹,

Lanier²,

Sena³

et al. 1986

Biochemistry

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“…Nevertheless, there appears to be a threshold temperature below which guanine nucleotides are no longer able to modulate the affinity state for agonists. This is evidenced by the finding that with 4 °C incubations, agonist affinity at both ß-and «[-adrenergic receptors was not altered by the presence of Gpp(NH)p. Similar findings with low incubation temperatures have been reported at dopamine receptors by Watanabe et al (1985) and at «,-adrenergic receptors by Lynch et al (1985).…”

Section: Resultssupporting

confidence: 89%

“…In membrane preparations, Gpp-(NH)p causes a rightward shift of agonist competition curves at both a,-and /?2-adrenergic receptors. While this was expected for ß-receptors, contradictory results have been presented with respect to the modulation of agonist binding by guanine nucleotides at «[-adrenergic receptors (Schwarz et al, 1985b;Hoffman et al, 1982;Lowry et al, 1951;Goodhardt et al, 1982;Lynch et al, 1985). Our observation that Gpp(NH)p converts agonist binding sites at «[-adrenergic receptors to a state of lower affinity suggests that, in analogy to the ß-adrenergic system, a ternary complex of agonist, receptor, and an as yet unidentified G protein may be involved in the signal transduction pathway of this adrenergic receptor subtype.…”

Section: Resultsmentioning

confidence: 99%

Agonist interactions at hepatic .alpha.1- and .beta.-adrenergic receptors: affinity-state regulation by guanine nucleotides and temperature

Schwarz¹,

Carter²,

Homcy³

et al. 1986

Biochemistry

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We investigated the binding characteristics of agonists to alpha 1- and beta-adrenergic receptors of intact liver cells, broken rat liver cell membranes, and detergent-solubilized preparations under varying experimental conditions, focusing on the different "states" of the receptor for agonists and the regulation of these states by temperature and guanine nucleotides. While only low-affinity binding of agonists to both receptor subtypes was evident in studies performed at 37 degrees C with solubilized preparations, biphasic competition curves for agonists were observed in both intact cells and membrane preparations; the majority of sites were of low affinity. In membrane preparations, the nonhydrolyzable GTP analogue Gpp(NH)p caused a rightward shift of agonist competition curves and a loss of high-affinity binding. These results are consistent with the involvement of guanine nucleotide binding proteins in both alpha 1- and beta-adrenergic transduction pathways. When competition studies were performed at 4 degrees C, receptor sites existed predominantly in the high-affinity configuration, in intact cells and membranes, as well as in soluble preparations. In contrast to the studies conducted at 37 degrees C, no Gpp(NH)p-induced conversion to the lower affinity state could be demonstrated in studies performed with membrane preparations at 4 degrees C. Thus, the high-affinity state of alpha 1- and beta-adrenergic receptors is stabilized at 4 degrees C in intact cells, membranes, and soluble preparations. After incubations had been performed at 37 degrees C, high-affinity binding of agonists could not be restored by subsequent incubation at 4 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

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“…Antagonist binding at 37 °C and agonist binding at 4 °C were insensitive to guanine nucleotides. These results are consistent with earlier reports (Goodhardt et al, 1982;Lynch et al, 1985;Schwartz et al, 1986) suggesting that agonists form a high-affinity guanine-nucleotide-sensitive complex with the a.-adrenoceptor.…”

Section: Characterization Of a L-adrenoceptorssupporting

confidence: 93%

Heparin and other polyanions uncouple α1-adrenoceptors from G-proteins

Dassò

Taylor

1991

Biochemical Journal

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Several polyanionic compounds antagonize the interaction between receptors and the G-proteins that regulate adenylate cyclase or K+ channels, possibly by binding to a basic stretch of the receptor that is proposed to mediate its interaction with the G-proteins. We have studied the effects of polyanions on the interaction between the liver alpha 1-adrenoceptor and the G-protein through which it stimulates polyphosphoinositide turnover. Heparin [concn. causing 50% of maximal effect (EC50) = 0.5 microM], Trypan Blue (EC50 7.1 microM) or suramin (EC50 2.1 microM) prevented formation of the high-affinity adrenaline-receptor-G-protein complex without affecting antagonist binding. After alkaline treatment of the membranes, previously reported to cause G-protein removal, binding of agonists was insensitive to both guanine nucleotides and heparin. We conclude that these polyanions uncouple the alpha 1-adrenoceptor from its G-protein, suggesting that similar coupling mechanisms may underlie receptor activation of the G-proteins that activate polyphosphoinositide hydrolysis and those that regulate adenylate cyclase. This action of heparin severely limits its utility as a selective antagonist of the Ins(1,4,5)P3 receptor in intact cells.

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Studies on the hepatic alpha 1-adrenergic receptor. Modulation of guanine nucleotide effects by calcium, temperature, and age.

Cited by 79 publications

References 30 publications

Agonist-induced isomerization of the .alpha.1-adrenergic receptor: kinetic analysis using broken-cell and solubilized preparations

Agonist-induced isomerization of the .alpha.1-adrenergic receptor: kinetic analysis using broken-cell and solubilized preparations

Agonist interactions at hepatic .alpha.1- and .beta.-adrenergic receptors: affinity-state regulation by guanine nucleotides and temperature

Heparin and other polyanions uncouple α1-adrenoceptors from G-proteins

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