Regulation of hepatocyte plasma membrane alpha 1-adrenergic receptors by 4 beta-phorbol 12-myristate 13-acetate.
The effect of phorbol 12-myristate 13-acetate (PMA) on hepatocyte alpha 1-adrenergic receptors was determined by [3H]prazosin binding to plasma membranes from control and PMA-treated hepatocytes. Membranes from hepatocytes incubated with PMA (1 microgram/ml) for 1 h exhibited a 40% decrease in alpha 1-adrenergic receptors (481 +/- 10 fmol/mg of protein; mean +/- S.E.M. for three separate experiments) relative to vehicle-treated (dimethylformamide) hepatocytes (802 +/- 91 fmol/mg of protein; n = 3), with no significant effect on the KD. The PMA-induced decrease in alpha 1-adrenergic receptors was maximal by 30 min and half-maximal inhibition of [3H]prazosin binding occurred with a PMA concentration of approx. 15 ng/ml. Pretreatment of hepatocytes with staurosporine (5 microM) blocked the effect of PMA, and 4 beta-phorbol 13-monoacetate was ineffective, suggesting the involvement of protein kinase C (PKC). Treatment of hepatocytes with primaquine (300 microM) for 15 min decreased hepatocyte plasma membrane alpha 1-adrenergic receptors by 34.0 +/- 2.4% (mean +/- S.E.M. of three experiments). Removal of primaquine allowed essentially complete recovery (98 +/- 4%; mean +/- S.E.M. for five separate experiments) of plasma membrane [3H]prazosin binding within 20 min, suggesting that the alpha 1-adrenergic receptor undergoes endocytotic recycling. Addition of PMA (1 microgram/ml) to hepatocytes immediately after removal of primaquine, completely inhibited the increase in plasma membrane alpha 1-adrenergic receptors relative to control cells, but had no effect on hepatocytes whose cell surface alpha 1-receptors remaining after primaquine treatment had been inactivated by alkylation. These observations suggested that activation of PKC may facilitate the internalization of the alpha 1-adrenergic receptor in hepatocytes.
Beeler
J F
JF
Department of Pharmacology, University of South Carolina School of Medicine, Columbia 29208.
Cooper
R H
RH
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D015536:Down-Regulation / Q000187:drug effects* / Q000502:physiology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure*; D008297:Male; D011224:Prazosin / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014316:Tritium
D018340:Receptors, Adrenergic, alpha-1; D014316:Tritium; D013755:Tetradecanoylphorbol Acetate; D011224:Prazosin