lithium-chloride and inositol-1-3-4-5-tetrakisphosphate

1. We have previously reported that the addition of noradrenaline to [3H]-inositol-labelled adult rat atria or isolated perfused hearts caused the release of inositol-1,4,5-trisphosphate, which was metabolized by dephosphorylation to inositol-4-monophosphate. Inositol-1,3,4,5-tetrakisphosphate and its dephosphorylation products were not detected. 2. In the current study, the addition of noradrenaline to [3H]-inositol-labelled adult rat cardiomyocytes caused the release of inositol-1,4,5-trisphosphate, which was metabolized in part by phosphorylation to inositol-1,3,4,5-tetrakisphosphate. 3. These results demonstrate that the isolation and culture of rat adult cardiomyocytes initiates enhanced generation of inositol-1,3,4,5-tetrakisphosphate. This change would be expected to enhance the calcium response of the cells to stimulation of alpha 1-adrenoceptors.

Topics: Animals; Cells, Cultured; Chlorides; Inositol; Inositol 1,4,5-Trisphosphate; Inositol Phosphates; Lithium; Lithium Chloride; Myocardium; Norepinephrine; Phosphorylation; Propranolol; Rats; Stimulation, Chemical; Tritium

Topics: Animals; Atropine; Carbachol; Cerebral Cortex; Chlorides; In Vitro Techniques; Inositol Phosphates; Kinetics; Lithium; Lithium Chloride; Rats; Receptors, Muscarinic

Inositol trisphosphate (IP3), a product of the phosphoinositide cycle, mobilizes intracellular Ca2+ in many cell types. New evidence suggests that inositol tetrakisphosphate (IP4), an IP3 derivative, may act as another second messenger to further alter calcium homeostasis. However, the function and mechanism of action of IP4 are presently unresolved. We now report evidence of muscarinic receptor-mediated accumulation of IP4 in bovine adrenal chromaffin cells, a classic neurosecretory system in which calcium movements have been well studied. Muscarine (0.4 mM) stimulated an increase in [3H]IP4 and [3H]IP3 accumulation in chromaffin cells and this effect was completely blocked by atropine (0.5 mM). [3H]IP4 accumulation was detectable within 15 sec, increased to a maximum by 30 sec and thereafter declined. 2,3-diphosphoglycerate, an inhibitor of IP3 and IP4 hydrolysis, enhanced accumulation of these inositol polyphosphates. The results provide the first evidence of a rapid inositol tetrakisphosphate response in adrenal chromaffin cells, which should facilitate the future resolution of the relationship between IP4 and calcium homeostasis.

Topics: 2,3-Diphosphoglycerate; Adrenal Medulla; Animals; Atropine; Cattle; Cells, Cultured; Chlorides; Diphosphoglyceric Acids; Inositol; Inositol 1,4,5-Trisphosphate; Inositol Phosphates; Kinetics; Lithium; Lithium Chloride; Muscarine; Receptors, Muscarinic; Second Messenger Systems

A short-term treatment with phorbol 12,13-dibutyrate (PDBu) was found to inhibit totally the epidermal growth factor (EGF)-stimulated phosphoinositide hydrolysis in A431 cells, whereas long-term pretreatment with PDBu, which is known to down regulate protein kinase C, induced a greater accumulation of the EGF-triggered inositol phosphate accumulation, particularly of Ins(1,3,4,5)P4. The increased Ins(1,4,5)P3/Ins(1,3,4,5)P4 formation in the PDBu long-term pretreated cells was coincident with the increased Ca2+ influx stimulated by EGF in the same cells. Since long-term pretreatment with PDBu was found to enhance the EGF signals, an explanation for the synergism between EGF and phorbol esters in the induction of DNA synthesis is provided.

Topics: Chlorides; Chromatography, High Pressure Liquid; Chromatography, Ion Exchange; Epidermal Growth Factor; Humans; Hydrolysis; Inositol 1,4,5-Trisphosphate; Inositol Phosphates; Lithium; Lithium Chloride; Phorbol 12,13-Dibutyrate; Phorbol Esters; Phosphatidylinositols; Protein Kinase C; Tumor Cells, Cultured

Dephosphorylation of inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] was measured in both the soluble and the particulate fractions of rat brain homogenates. Analysis of the hydrolysis of [4,5-32P]Ins(1,3,4,5)P4 showed that for both fractions the 5-phosphate of Ins(1,3,4,5)P4 was removed and inositol 1,3,4-trisphosphate [Ins(1,3,4)P3] was specifically produced. In the soluble fraction, Ins(1,3,4)P3 was further hydrolysed at the 1-phosphate position to inositol 3,4-bisphosphate[Ins(3,4)P2]. DEAE-cellulose chromatography of the soluble fraction separated the phosphatase activities into three peaks. The first hydrolysed both Ins(1,3,4,5)P4 and inositol 1,4,5-trisphosphate, the second inositol 1-phosphate and the third Ins(1,3,4)P3 and inositol 1,4-bisphosphate, [Ins(1,4)P2]. Further purification of the third peak on either Sephacryl S-200 or Blue Sepharose could not dissociate these two activities [i.e. with Ins(1,4)P2 and Ins(1,3,4)P3 as substrates]. The dephosphorylation of Ins(1,3,4)P3 could be inhibited by the addition of Li+.

Topics: Animals; Brain; Chlorides; Chromatography, DEAE-Cellulose; Chromatography, High Pressure Liquid; Hydrolysis; In Vitro Techniques; Inositol Phosphates; Inositol Polyphosphate 5-Phosphatases; Lithium; Lithium Chloride; Phosphoric Monoester Hydrolases; Phosphorylation; Rats; Solubility; Substrate Specificity; Sugar Phosphates