The broad, long-term objectives are to throw further light on the biochemistry and biological significance of the phosphoinositide signalling system. More specifically, (1) What is the role of inositol 1,2-cyclic 4,5-trisphosphate (cIP3) in the phosphoinositde signalling process? Paramount on the list will be a search for a cIP3 receptor unique from the inositol (1,4,5)-trisphosphate (I(1,4,5)P3) receptor because the discovery of such a receptor would provide very strong evidence for a second messenger function for cIP3. Possible second messenger or regulatory roles will be tested in permeabilized acini and cell-free fractions, such as (a) inhibition of binding of I(1,4,5)P3 at its receptor. This could dampen Ca2+ mobilization after its initial spike; (b) synergism between cIP3 and I(1,4,5)P3 or I(1,3,4,5)P3 on Ca2+ influx; (c) activation by cIP3 of PI hydrolysis in the endoplasmic reticulum (ER). (2) What is the function of free arachidonic acid (AA) and metabolites in agonist-stimulated cells? We will examine the capability of AA to release Ca2+ from permeabilized and unpermeabilized pancreatic acinar cells. We will also study the activation of protein kinase C (PKC) by AA alone or in combination with activators of PKC, such as Ca2+, diacylglycerol (DAG), and phosphatidylserine. (3) Is there direct phosphodiesteratic cleavage of PI in the ER, or is the agonist-stimulated loss of PI strictly by phosphorylation of PI to form PIP and then PIP2 in the plasma membrane (PM)? Microsomes derived from the ER will be incubated with cIP3, I(1,4,5)P3, DAG, Ca2+ etc., which may be messengers which could trigger direct PI breakdown. Also, direct breakdown could be established if we are able to show a formation of I(l)P in excess of that which could be formed by the I(1,4,5)P3 degradation pathway. (4) We will study the formation of cIP3 and AA in the central nervous system. We will concentrate mainly on the cerebellum, which has the highest density of IP3 receptors and which releases substantial amounts of prostaglandins in response to low concentrations of acetylcholine. (5) We are initiating molecular-biological studies on the phosphoinositide signalling system. We have essentially purified the 53 Kd PIP-kinase band on SDS-PAGE from human red cells and are preparing antibodies to screen a human brain cDNA library in the expression vector, lambda GT11.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL016318-35
Application #
2214969
Study Section
Physiological Chemistry Study Section (PC)
Project Start
1978-09-01
Project End
1995-06-30
Budget Start
1993-07-01
Budget End
1995-06-30
Support Year
35
Fiscal Year
1993
Total Cost
Indirect Cost
Name
University of Wisconsin Madison
Department
Pharmacology
Type
Schools of Medicine
DUNS #
161202122
City
Madison
State
WI
Country
United States
Zip Code
53715
Dixon, J F; Hokin, L E (1998) Lithium acutely inhibits and chronically up-regulates and stabilizes glutamate uptake by presynaptic nerve endings in mouse cerebral cortex. Proc Natl Acad Sci U S A 95:8363-8
Dixon, J F; Hokin, L E (1997) The antibipolar drug valproate mimics lithium in stimulating glutamate release and inositol 1,4,5-trisphosphate accumulation in brain cortex slices but not accumulation of inositol monophosphates and bisphosphates. Proc Natl Acad Sci U S A 94:4757-60
Hokin, L E (1996) History of phosphoinositide research. Subcell Biochem 26:1-41
Los, G V; Artemenko, I P; Hokin, L E (1996) Phosphoinositide signalling in human neuroblastoma cells: biphasic effect of Li+ on the level of the inositolphosphate second messengers. Adv Enzyme Regul 36:245-64
Hokin, L E; Dixon, J F; Los, G V (1996) A novel action of lithium: stimulation of glutamate release and inositol 1,4,5 trisphosphate accumulation via activation of the N-methyl D-aspartate receptor in monkey and mouse cerebral cortex slices. Adv Enzyme Regul 36:229-44
Los, G V; Artemenko, I P; Hokin, L E (1995) Time-dependent effects of lithium on the agonist-stimulated accumulation of second messenger inositol 1,4,5-trisphosphate in SH-SY5Y human neuroblastoma cells. Biochem J 311 ( Pt 1):225-32
Dixon, J F; Los, G V; Hokin, L E (1994) Lithium stimulates glutamate ""release"" and inositol 1,4,5-trisphosphate accumulation via activation of the N-methyl-D-aspartate receptor in monkey and mouse cerebral cortex slices. Proc Natl Acad Sci U S A 91:8358-62
Su, X; Chen, F; Hokin, L E (1994) Cloning and expression of a novel, highly truncated phosphoinositide-specific phospholipase C cDNA from embryos of the brine shrimp, Artemia. J Biol Chem 269:12925-31
Dixon, J F; Hokin, L E (1994) Lithium stimulates accumulation of second-messenger inositol 1,4,5-trisphosphate and other inositol phosphates in mouse pancreatic minilobules without inositol supplementation. Biochem J 304 ( Pt 1):251-8
Hokin, L E (1993) Lithium increases accumulation of second messenger inositol 1,4,5-trisphosphate in brain cortex slices in species ranging from mouse to monkey. Adv Enzyme Regul 33:299-312

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