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Predicate | Object |
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rdf:type | |
lifeskim:mentions | |
pubmed:issue |
1
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pubmed:dateCreated |
1989-8-22
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pubmed:abstractText |
We compared the effects of methoxamine on alpha 1-adrenergic receptor-mediated phosphorylase activation in rat hepatocytes and rabbit aorta. Although methoxamine is a potent agonist in activating phosphorylase of rabbit aorta, it had little effect in rat hepatocytes. Using the phenoxybenzamine inactivation method, we found that the quantitative relationship between 125I-BE2254 (125I-BE) binding capacity and maximal norepinephrine-stimulated phosphorylase activation was nonlinear in rabbit aorta, whereas it was linear in rat hepatocytes. The potency of methoxamine in inhibiting specific 125I-BE binding is significantly (p less than 0.05) higher in rabbit aorta (Kd, 96.4 +/- 7.7 microM), compared with rat hepatocytes (Kd, 283 +/- 16 microM). However, these quantitative differences could not fully explain the blunted [Ca2+]c and phosphorylase responses to methoxamine in rat hepatocytes. Treatment with chlorethylclonidine dose dependently suppressed 125I-BE binding sites and norepinephrine-induced phosphorylase activation in rat hepatocytes, whereas in rabbit aorta it resulted in only a 31% decrease in 125I-BE binding sites, with little effect on phosphorylase activation. Furthermore, alpha 1-adrenergic receptor-mediated cellular events of phosphatidylinositol (PI) hydrolysis and phosphorylase activation were unaffected by the removal of extracellular Ca2+ in rat hepatocytes, whereas both responses were markedly attenuated in rabbit aorta. The results indicate that two different alpha 1-adrenergic receptor subtypes activate glycogen phosphorylase, through different mechanisms for increasing [Ca2+]c in the two systems. In rat hepatocytes, alpha 1 receptors are closely linked to PI hydrolysis and Ca2+ release from intracellular stores and cause phosphorylase activation. In rabbit aorta, on the other hand, activation of alpha 1 receptors increases [Ca2+]c by Ca2+ influx from the extracellular fluid as well as by Ca2+ release, and both PI hydrolysis and phosphorylase activation are caused mainly by the Ca2+ entry. Methoxamine interacts with both chlorethylclonidine-sensitive and -insensitive alpha 1 receptor subtypes but selectively stimulates the alpha 1 receptor subtype that closely couples with the Ca2+ influx.
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pubmed:language |
eng
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pubmed:journal | |
pubmed:citationSubset |
IM
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pubmed:chemical |
http://linkedlifedata.com/resource/pubmed/chemical/BE 2254,
http://linkedlifedata.com/resource/pubmed/chemical/Calcium,
http://linkedlifedata.com/resource/pubmed/chemical/Clonidine,
http://linkedlifedata.com/resource/pubmed/chemical/Epinephrine,
http://linkedlifedata.com/resource/pubmed/chemical/Inositol Phosphates,
http://linkedlifedata.com/resource/pubmed/chemical/Methoxamine,
http://linkedlifedata.com/resource/pubmed/chemical/Phenethylamines,
http://linkedlifedata.com/resource/pubmed/chemical/Phenylephrine,
http://linkedlifedata.com/resource/pubmed/chemical/Phosphorylases,
http://linkedlifedata.com/resource/pubmed/chemical/Receptors, Adrenergic, alpha,
http://linkedlifedata.com/resource/pubmed/chemical/Tetralones,
http://linkedlifedata.com/resource/pubmed/chemical/chlorethylclonidine
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pubmed:status |
MEDLINE
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pubmed:month |
Jul
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pubmed:issn |
0026-895X
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pubmed:author | |
pubmed:issnType |
Print
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pubmed:volume |
36
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pubmed:owner |
NLM
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pubmed:authorsComplete |
Y
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pubmed:pagination |
166-76
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pubmed:dateRevised |
2006-11-15
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pubmed:meshHeading |
pubmed-meshheading:2546049-Animals,
pubmed-meshheading:2546049-Calcium,
pubmed-meshheading:2546049-Clonidine,
pubmed-meshheading:2546049-Enzyme Activation,
pubmed-meshheading:2546049-Epinephrine,
pubmed-meshheading:2546049-Inositol Phosphates,
pubmed-meshheading:2546049-Male,
pubmed-meshheading:2546049-Methoxamine,
pubmed-meshheading:2546049-Phenethylamines,
pubmed-meshheading:2546049-Phenylephrine,
pubmed-meshheading:2546049-Phosphorylases,
pubmed-meshheading:2546049-Rabbits,
pubmed-meshheading:2546049-Rats,
pubmed-meshheading:2546049-Rats, Inbred Strains,
pubmed-meshheading:2546049-Receptors, Adrenergic, alpha,
pubmed-meshheading:2546049-Tetralones
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pubmed:year |
1989
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pubmed:articleTitle |
Glycogen phosphorylase activation by two different alpha 1-adrenergic receptor subtypes: methoxamine selectively stimulates a putative alpha 1-adrenergic receptor subtype (alpha 1a) that couples with Ca2+ influx.
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pubmed:affiliation |
Department of Pharmacology, Yamanashi Medical College, Japan.
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pubmed:publicationType |
Journal Article,
In Vitro
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