Pigment dispersion in frog melanophores can be induced by a phorbol ester or stimulation of a recombinant receptor that activates phospholipase C.
Pigment dispersion in frog melanophores is classically mediated by receptors that activate protein kinase A via an elevation of intracellular cyclic AMP. Here, 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of protein kinase C, is found to induce pigment dispersion. To demonstrate that an increase in cAMP is not required for the melanosome movement, a murine bombesin receptor was expressed in the melanophores. When these cells were treated with bombesin, they accumulated intracellular inositol phosphates but not cAMP and dispersed their pigment. Four agonists, one partial agonist, and two antagonists for the bombesin receptor were compared for their ability to induce or block bombesin-induced pigment dispersion. In all cases, the degree of pigment dispersion followed simple equilibrium reactions. The resulting dose-response curves allowed for the determination of the effective concentration for half-maximal pigment dispersion (EC50) or half-maximal inhibition of bombesin-stimulated pigment dispersion (IC50) for the peptides. As the pigment dispersion assay can rapidly evaluate chemicals for their effects on receptors that activate phospholipase C via a functional assay, it has potential utility for investigations of ligand-receptor interactions and for massive drug screening.
Graminski
G F
GF
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510.
Jayawickreme
C K
CK
Potenza
M N
MN
Lerner
M R
MR
D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004277:DNA, Single-Stranded; D004789:Enzyme Activation; D007295:Inositol Phosphates / Q000378:metabolism; D008547:Melanophores / Q000187:drug effects / Q000378:metabolism*; D008969:Molecular Sequence Data; D010860:Pigments, Biological / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000187:drug effects* / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000378:metabolism*; D014982:Xenopus laevis
D004277:DNA, Single-Stranded; D007295:Inositol Phosphates; D010860:Pigments, Biological; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; D000242:Cyclic AMP; D010738:Type C Phospholipases; D013755:Tetradecanoylphorbol Acetate