Halothane facilitates the translocation of GRK-2 and phosphorylation of beta2-adrenergic receptor in rat synaptosomes.
OBJECTIVE
To examine the effect of halothane on beta2-adrenergic receptor phosphorylation and on G-protein coupled receptor kinase (GRK), responsible for beta2-receptor downregulation.


METHODS
Rat forebrain synaptosomes were incubated for 30 min with halothane 1 or 2%. The cytosolic and membrane fractions were separated, and phosphorylation activity of recombinant beta2-adrenergic receptor was quantified autoradiographically using 32P labeled adenosine triphosphate. Phosphorylation activity of a specific GRK-2 substrate, was examined by measuring 32P binding. Subcellular localization of the enzyme was immunologically analyzed by Western blotting.


RESULTS
Halothane 2% decreased the phosphorylation activity of the recombinant receptor in the cytosol fraction, regardless of 10 microM isoproterenol (ISP) (P<0.01), which activity in the membrane fraction was increased (P<0.01). Phosphorylation activity of the synthetic peptide decreased in the cytosol obtained from synaptosomes exposed to halothane 2% (P<0.05). In contrast, activity in the membrane increased by exposure to halothane 2% (P<0.01). The concentration of GRK-2 decreased in the cytosol obtained from synaptosomes exposed to halothane 1% or 2% (decreases of 8.3+/-1.2% @ 1%, and 18.0+/-2.1% @ 2%, P<0.05). In the membrane, exposure to halothane 1% or 2% increased the GRK-2 amount dose dependently (22.5+/-3.1% @ 1%, and by 45.7+/-6.1% @ 2%, P<0.01).


CONCLUSIONS
Halothane could facilitate translocation of GRK-2 and possibly promote the downregulation of beta2-adrenergic receptors in the synaptic membrane. The anesthetic action and hemodynamic suppressive action of halothane may be related to this phenomenon.
Saito
S
S
Department of Anesthesiology and Reanimatology, Gunma University School of Medicine, Maebashi, Japan. shigerus@news.sb.gunma-u.ac.jp
Kadoi
Y
Y
Ohyama
A
A
Goto
F
F
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D006221:Halothane / Q000494:pharmacology*; D008297:Male; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D051552:beta-Adrenergic Receptor Kinases
D018685:Anesthetics, Inhalation; D018343:Receptors, Adrenergic, beta-2; D017868:Cyclic AMP-Dependent Protein Kinases; D051552:beta-Adrenergic Receptor Kinases; D006221:Halothane