Guinea pig hepatocyte alpha 1A-adrenoceptors: characterization, signal transduction and regulation.
Activation of guinea pig hepatocyte alpha 1-adrenoceptors increases phosphatidylinositol (PI) labeling, [3H]inositol phosphate production and phosphorylase activity. These adrenergic actions were not altered by pretreatment with chlorethylclonidine but were blocked by 5-methyl urapidil and prazosin (the former being 3- to 10-fold more potent than the latter), indicating that alpha 1A-adrenoceptors were involved. When the cells were incubated in buffer without calcium and containing EGTA, the alpha 1A-adrenergic stimulation of PI labeling was diminished but not abolished and that of phosphorylase was not affected. The alpha 1A-adrenergic effects were insensitive to pertussis toxin treatment. Phorbol myristate acetate inhibited the alpha 1A-adrenergic actions, although at relatively large concentrations, and also those of other agents such as angiotensin II and NaF. Our data clearly indicate that guinea pig hepatocytes express alpha 1A-adrenoceptors whose activation stimulates phosphoinositide turnover, via a pertussis toxin-insensitive process; the alpha 1A-adrenergic effects were at least partially independent of extracellular calcium.
García-Sáinz
J A
JA
Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, D.F., Mexico.
Romero-Avila
T
T
Olivares-Reyes
J A
JA
Macías-Silva
M
M
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D003000:Clonidine / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000032:analysis; D008099:Liver / Q000737:chemistry* / Q000166:cytology; D008297:Male; D037342:Pertussis Toxin; D010716:Phosphatidylinositols / Q000032:analysis* / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014316:Tritium; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D010761:Phosphorus Radioisotopes; D011942:Receptors, Adrenergic, alpha; D010566:Virulence Factors, Bordetella; D014316:Tritium; C051731:chlorethylclonidine; D004533:Egtazic Acid; D037342:Pertussis Toxin; D003000:Clonidine; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium