title: Phorbol diester modulates alpha-adrenergic receptor-coupled calcium efflux and alpha-adrenergic receptor number in cultured vascular smooth muscle cells.
abstract: The phorbol ester 12-O-tetradecanoyl phorbol-13-acetate was used to probe the role of protein kinase-C in the modulation of alpha-adrenergic receptor-coupled calcium efflux in cultured vascular smooth muscle cells derived from rabbit aorta. Exposure of cells to 12-O-tetradecanoyl phorbol-13-acetate for 6 minutes caused a concentration-related (maximum effect at greater than or equal to 10 nM) increase in calcium-45 efflux from preloaded cells. Maximum calcium-45 efflux stimulated by 12-O-tetradecanoyl phorbol-13-acetate was equivalent to maximum norepinephrine-stimulated calcium-45 efflux, and maximally effective concentrations of 12-O-tetradecanoyl phorbol-13-acetate and norepinephrine together were no more potent than either drug alone. Exposure of cells to 12-O-tetradecanoyl phorbol-13-acetate for periods of 1-24 hours resulted in complete loss of norepinephrine-stimulated calcium-45 efflux and a much slower, concentration-related reduction in alpha-adrenergic receptor number, with a maximum reduction of 50-60% at 12-O-tetradecanoyl phorbol-13-acetate concentrations greater than or equal to 10 nM. Twenty-four hours of exposure to 12-O-tetradecanoyl phorbol-13-acetate (10 nM) and norepinephrine (10 microM) together caused no greater reduction in [3H]prazosin binding than did norepinephrine alone. 12-O-tetradecanoyl phorbol-13-acetate had no effect on [3H]prazosin-binding affinity. These data suggest an important role for protein kinase-C in both the acute excitation-contraction coupling of vascular smooth muscle alpha-adrenergic receptors, and in the long-term modulation of vascular alpha-adrenergic receptor responsiveness.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology; D010704:Phorbols / Q000494:pharmacology*; D011224:Prazosin / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D010704:Phorbols; D011942:Receptors, Adrenergic, alpha; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D009638:Norepinephrine; D011224:Prazosin