title: Stimulation of Na+/phosphate cotransport in LLC-PK1 cells by 12-O-tetradecanoylphorbol 13-acetate (TPA).
abstract: We have tested for the effect of the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) on Na+/phosphate cotransport in an established epithelial cell line of renal origin (LLC-PK1). Incubation of LLC-PK1 cells with TPA produced an increase in Na+/phosphate (Pi) cotransport. The maximal response was reached at a TPA concentration of 10 ng/ml. Other phorbol esters which have no potency or a smaller one to activate protein kinase C had no effect on Na+/Pi cotransport. Incubation of LLC-PK1 cells with 10 ng/ml TPA for 8 h led to a 300% increase in Na+/Pi cotransport; in the presence of cycloheximide the increase amounted only to a 100% and was reached within 2 h. Kinetic analysis of Na+/Pi cotransport indicated an increase in the apparent Vmax without an effect on the apparent Km. The increased Pi transport was retained in isolated apical vesicles. Na+-dependent alanine transport into LLC-PK1 monolayers was affected by TPA administration in a similar manner. TPA had under the chosen experimental conditions no effect on [3H]thymidine incorporation into DNA excluding a general proliferative effect. We conclude that TPA via activation of protein kinase C regulates the number of operating transport systems. As also other Na+-coupled transport systems are influenced, the TPA effect appears to be related to the expression of a general 'adaptive' alteration of membrane transport in LLC-PK1 cells.
mesh_terms: D000409:Alanine / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D002474:Cell-Free System; D003513:Cycloheximide / Q000494:pharmacology; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D010703:Phorbol Esters / Q000494:pharmacology; D010704:Phorbols / Q000494:pharmacology*; D010710:Phosphates / Q000378:metabolism*; D014176:Protein Biosynthesis; D012964:Sodium / Q000378:metabolism*; D013268:Stimulation, Chemical; D013329:Structure-Activity Relationship; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D010703:Phorbol Esters; D010704:Phorbols; D010710:Phosphates; D003513:Cycloheximide; D012964:Sodium; D013755:Tetradecanoylphorbol Acetate; D000409:Alanine