In brain cells, Li inhibits the inositol turnover cycle and increases the production of second messengers, in particular diacylglycerol (DAG), whose primary effector is protein kinase C (PKC) Previous studies from our laboratory in low K sheep red blood cells (LK SRBCs) showed that Li first stimulated and then inhibited KC1 COT with increasing internal Li concentrations ([Li]i) without affecting internal pH. Here, we test the hypothesis that Li affects KCl COT through a PKC-dependent pathway involving downstream regulation of mitogen-activating protein kinase (MAPK), associated serine/threonine kinases and protein phosphatase 1 (PP1) To test this hypothesis, LK SRBCs were loaded with increasing [Li]i up to 20 mmol/liter original cells (LOC) for its effect on DAG content, determined by using thin layer chromatography (TLC) and Imagcalc software In addition, the effects of the phorbol ester TPA (a PKC modulator, 100 nM), calyculin (a PP1 inhibitor, 20 nM) and PD098059 (a MAPK kinase inhibitor, 50 uM) were tested on KCl COT activity, measured as the ouabain-insensitive Cl-dependent K efflux. Li-loading induced both cellular swelling and KCl COT inhibition (up to 50%) in a Li-dependent fashion. Cellular DAG increased by 200% with increasing [Li]i up to 5 mmol/LOC followed by a slow decline at higher [Li]i Li-induced inhibition of KCl COT was reversible with acute (up to 1 h) exposure to TPA. Acute exposure to TPA stimulated KCl COT by 31 % in non-loaded cells whereas chronic exposure (>1h) mimicked Li-induced inhibition Calyculin and PD098059 inhibited KCl COT by 83% and 29%, respectively. These results support the hypothesis that Li modulates KCl COT through a PKC-dependent pathway.
|Original language||English (US)|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology