Alpha 1-adrenergic receptors in the brain: characterization in astrocytic glial cultures and comparison with neuronal cultures.
Binding of [125I]HEAT to membranes prepared from primary cultures of astrocytic glial cells was time-dependent and 70-85% specific. Various adrenergic agonists and antagonists competed for [125I]HEAT binding according to the potencies of prazosin greater than, yohimbine greater than or equal to, clonidine, norepinephrine (NE), and propranolol. Scatchard analysis showed the Bmax of 209 fmol/mg protein and a Kd of 184 pM for [125I]HEAT binding by astrocytic glial membranes. Pretreatment of astrocytes with NE resulted in a dose-dependent downregulation of [125I]HEAT binding sites with a maximal response observed after 8 h at 100 microM NE. Removal of NE from cultures after pretreatment resulted in a time- and protein synthesis-dependent recovery of binding sites to control levels within 120 h. Incubation of astrocytic glial cultures with NE stimulated phosphoinositide (PI) hydrolysis in a time- and dose-dependent manner with a maximal stimulation of 2-fold observed in 60 min by 100 microM NE. Clonidine expressed differential effects on alpha 1-adrenergic receptors of the neuronal and astrocytic glial cultures. Pretreatment with 10 microM clonidine caused a 40% decrease in the Bmax of [125I]HEAT binding without influencing the Kd value in neuronal cultures. This downregulatory effect of clonidine was associated with a reduction in the ability of NE to stimulate PI hydrolysis in clonidine pretreated cells. In contrast to neuronal cultures, clonidine neither downregulated [125I]HEAT binding sites nor stimulated PI hydrolysis in glial cultures.
Puig
J F
JF
Department of Physiology, University of Florida College of Medicine, Gainesville 32610.
Pacitti
A J
AJ
Guzman
N J
NJ
Crews
F T
FT
Sumners
C
C
Raizada
M K
MK
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002478:Cells, Cultured; D003000:Clonidine / Q000494:pharmacology; D007700:Kinetics; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D010716:Phosphatidylinositols; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D003000:Clonidine; D009638:Norepinephrine