Purpose: To examine the effect of halothane on beta 2-adrenergic receptor p
hosphorylation and on G-protein coupled receptor kinase (GRK), responsible
for beta 2-receptor downregulation.
Methods: Rat forebrain synaptosomes were incubated for 30 min with halothan
e 1 or 2%. The cytosolic and membrane fractions were separated, and phospho
rylation activity of recombinant beta 2-adrenergic receptor was quantified
autoradiographically using P-32 labeled adenosine triphosphate. Phosphoryla
tion activity of a specific GRK-2 substrate, was examined by measuring P-32
binding. Subcellular localization-of the enzyme was immunologically analyz
ed by Western blotting.
Results: Halothane 2% decreased the phosphorylation activity of the recombi
nant receptor in the cytosol fraction, regardless of 1 mu M 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 c
ontrast, 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%, a
nd by 45.7 +/- 6.1% @ 2%, P < 0.01).
Conclusion: Halothane could facilitate translocation of GRK-2 and possibly
promote the downregulation of O-2-adrenergic receptors in the synaptic memb
rane. The anesthetic action and hemodynamic suppressive action of halothane
may be related to this phenomenon.