Acute and long-term inhibition of agonist-stimulated phosphoinositide hydrolysis by pulse treatment of cerebellar granule cells with TPA.
Acute pretreatment (30 min) of primary cultures of cerebellar granule cells with TPA (10 nM) resulted in a decrease in carbachol-and glutamate-stimulated phosphoinositide hydrolysis, but not in basal levels of PI hydrolysis. To investigate the mechanism of TPA action, phospholipase C was assayed in membranes prepared from cerebellar granule cells acutely treated with TPA. TPA had no effect on basal, GTP gamma S-, NaF-, and calcium-stimulated phospholipase C when compared with membranes prepared from vehicle-treated cells. The effects of pulsing with TPA (30-min pulse, 10 nM) on agonist-stimulated PI hydrolysis were studied 1, 3, and 5 or 6 d after TPA treatment. TPA treatment results in a statistically significant decrease in glutamate-stimulated PI hydrolysis, and a slight reduction of carbachol-stimulated PI hydrolysis when compared to temporally matched controls. Measurements in membranes prepared from TPA-treated vs control cells 1, 3, and 5 d after treatment showed that calcium- and NaF-stimulated phospholipase C activity was significantly decreased at all days tested, whereas GTP gamma S-stimulated phospholipase C activity was significantly decreased only at d 3. These data demonstrate differences in the acute vs long-term effects of TPA treatment on agonist-stimulated PH hydrolysis, and suggest that the acute effects may be mediated at the level of the receptor, whereas long-term effects of TPA on PI hydrolysis may be mediated by deficits in effector function.
Paulsen
R E
RE
Fidia-Georgetown Institute for the Neurosciences, Georgetown University School of Medicine, Washington, DC 20007.
Raulli
R
R
Grayson
D R
DR
Wroblewski
J T
JT
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000378:metabolism; D018698:Glutamic Acid / Q000494:pharmacology; D006868:Hydrolysis; D010716:Phosphatidylinositols / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D016318:Quisqualic Acid / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000378:metabolism
D010716:Phosphatidylinositols; D018698:Glutamic Acid; D016318:Quisqualic Acid; D002217:Carbachol; D011493:Protein Kinase C; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate