Characterization of the alpha 1B-adrenoceptors of catfish hepatocytes: functional and binding studies.
In catfish hepatocytes (Ictalurus punctatus) alpha 1-adrenergic activation by epinephrine or norepinephrine increased cytosol Ca2+ concentration. This effect was inhibited by alpha 1-adrenergic antagonists with the potency order WB4101 > benoxathian > or = 5-methylurapidil > phentolamine > (+)niguldipine. Pretreatment with the irreversible antagonist, chloroethylclonidine, reduced the alpha 1-adrenergic effect. alpha 1-Adrenergic stimulation also increased the resynthesis of phosphatidylinositol in whole cells. In liver membranes, a relatively small (33 fmol/mg of protein) number of sites with high affinity (Kd 100 pM) for the radioligand [125I]HEAT was detected. Binding competition experiments showed the following orders of potency: (1) for agonists, oxymetazoline > epinephrine > or = norepinephrine > methoxamine; (2) for antagonists, prazosin > WB4101 > benoxathian > or = 5-methylurapidil > phentolamine > (+)niguldipine. Membrane pretreatment with chloroethylclonidine markedly reduced [125I]HEAT binding. Good correlation was observed between the radioligand binding studies and the functional data with isolated cells. The present data suggest that the alpha 1-adrenoceptor present in catfish liver cells belongs to the alpha 1B subtype.
García-Sáinz
J A
JA
Departamento de Bioenergética, Universidad Nacional Autónoma de México, Mexico City.
Olivares-Reyes
J A
JA
Macías-Silva
M
M
Villalobos-Molina
R
R
D000316:Adrenergic alpha-Agonists / Q000378:metabolism; D000317:Adrenergic alpha-Antagonists / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004837:Epinephrine / Q000494:pharmacology; D007059:Ictaluridae; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010109:Oxymetazoline / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism; D011433:Propranolol / Q000494:pharmacology; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000378:metabolism*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D010716:Phosphatidylinositols; D018340:Receptors, Adrenergic, alpha-1; D010109:Oxymetazoline; D011433:Propranolol; D002118:Calcium; D009638:Norepinephrine; D004837:Epinephrine