lithium-chloride and phosphatidylinositol-4-phosphate

The effects of in vitro histotoxic hypoxia (0.5 mM KCN) on potassium-stimulated phosphatidylinositol turnover were determined. In rat cortical slices that were prelabeled with [2-3H]inositol, depolarization with 60 mM KCl increased [2-3H]inositol monophosphate and [2-3H]inositol bisphosphate accumulation in a Ca2+-dependent manner. At early times (10 s and 1 min), histotoxic hypoxia enhanced potassium-stimulated [2-3H]inositol monophosphate and inositol bisphosphate accumulation. Under basal conditions, hypoxia did not alter the accumulation of [2-3H]inositol phosphates. These results are consistent with the following hypothesis. The hypoxic-induced increase in cytosolic free calcium that we reported previously may lead to the early stimulation of inositol phosphates formation during hypoxia through activation of phospholipase C. The impairment of inositol phosphates formation during more prolonged hypoxia may be due to negative feedback regulation of the phosphatidylinositol cascade by protein kinase C or to a reduction in ATP levels.

Topics: Animals; Calcium; Cerebral Cortex; Chlorides; Hypoxia; Inositol; Lithium; Lithium Chloride; Male; Phosphatidylinositol 4,5-Diphosphate; Phosphatidylinositol Phosphates; Phosphatidylinositols; Potassium Chloride; Potassium Cyanide; Rats; Rats, Inbred Strains

Stimulation by the tripeptide N-formyl norleucyl leucyl phenylalanine (FNLLP) of the guinea pig alveolar macrophage gives rise to transient production of superoxide anion (O2-). Components of the phosphatidyl inositol (PI) cycle (phosphatidic acid (PA), phosphatidyl inositol-4,5-bisphosphate (TPI) and phosphatidyl inositol-4-phosphate (DPI) were monitored using 32P in order to examine the possible association of this cycle with the FNLLP-stimulated production of O2-. Macrophage stimulation by FNLLP led to an increased flux of metabolites through the PI cycle. The level of 32P label in both TPI and DPI rapidly decreased upon exposure to FNLLP, followed by a 5-min period during which the 32P label in TPI and DPI approached prestimulated levels. During this period, there was a fivefold increase in 32P-PA. It is suggested that diacylglycerol (DAG) is the O2- -activating intermediate in the stimulated mechanism, as evidenced by the buildup of PA (for which DAG is the precursor) in parallel with the time course of O2- production. The importance of continued cycling of PI in the stimulated mechanism is demonstrated by the inhibition by LiCl of the extent, but not the initial rate, of both O2- production and the formation of 32P-PA upon peptide stimulation after 1-h preincubation with 10 mM LiCl. The influence of calcium on this mechanism was also examined. It has previously been demonstrated that intracellular availability of calcium can influence the rate and extent of O2- production. In cells preloaded with quin-2, which acts as a high-affinity sink for calcium in the cytosol, the initial rate of FNLLP-stimulated O2- production is inhibited in low (10 microM) extracellular calcium medium. High extracellular calcium (1 mM) completely reverses this inhibition and also significantly extends the time course of O2- production in both quin-2 and control cells (Stickle et al., 1984). In parallel with these effects on O2- production, varying calcium conditions is demonstrated to influence the rate and extent of PA formation. These same calcium conditions were found to have little or no effect on the initial unstimulated levels of TPI, DPI, and PA. These results indicate that the influence of an intracellular pool of calcium on O2- production may be via its influence on stimulated PI turnover.

Topics: Animals; Calcium; Chlorides; Guinea Pigs; In Vitro Techniques; Lithium; Lithium Chloride; Macrophage Activation; Macrophages; Male; Oligopeptides; Phosphatidic Acids; Phosphatidylinositol 4,5-Diphosphate; Phosphatidylinositol Phosphates; Phosphatidylinositols; Pulmonary Alveoli; Superoxides