Phosphatidylinositol Pathway Research Articles

A novel pathway of cellular phosphatidylinositol(3,4,5)-trisphosphate synthesis is regulated by oxidative stress.

Phosphatidylinositol-3,4,5-trisphosphate [PtdIns(3,4,5)P(3)] is a key second messenger found ubiquitously in higher eukaryotic cells. The activation of Class I phosphoinositide 3-kinases and the subsequent production of PtdIns(3,4,5)P(3) is an important cell signaling event that has been causally linked to the activation of a variety of downstream cellular processes, such as cell migration and proliferation. Although numerous proteins regulating a variety of biological pathways have been shown to bind PtdIns(3,4,5)P(3), there are no data to demonstrate multiple mechanisms for PtdIns(3,4,5)P(3) synthesis in vivo. In this study, we demonstrate an alternative pathway for the in vivo production of PtdIns(3,4,5)P(3) mediated by the action of murine Type Ialpha phosphatidylinositol 4-phosphate 5-kinase (Type Ialpha PIPkinase), an enzyme best characterized as regulating cellular PtdIns(4,5)P(2) levels. Analysis of this novel pathway of PtdIns(3,4,5)P(3) synthesis in cellular membranes leads us to conclude that in vivo, Type Ialpha PIPkinase also acts as a PtdIns(3,4)P(2) 5-kinase. We demonstrate for the first time that cells actually contain an endogenous PtdIns(3,4)P(2) 5-kinase, and that during oxidative stress, this enzyme is responsible for PtdIns(3,4,5)P(3) synthesis. Furthermore, we demonstrate that by upregulating the H(2)O(2)-induced PtdIns(3,4,5)P(3) levels using overexpression studies, the endogenous PtdIns(3,4)P(2) 5-kinase is likely to be Type Ialpha PIPkinase. We describe for the first time a novel in vivo activity for Type Ialpha PIPkinase, and a novel pathway for the in vivo synthesis of functional PtdIns(3,4,5)P(3), a key lipid second messenger regulating a number of diverse cellular processes.

PHOSPHATIDYLINOSITOL 3-KINASE REGULATES PROLIFERATION OF RAW 264.7 MACROPHAGES

Phosphatidylinositol 3-kinase (PI3-kinase) is an enzyme that acts as a direct biochemical link between a novel phosphatidylinositol pathway and a number of proteins containing intrinsic or associated kinase activities. Here we demonstrate that wortmannin, PI3-kinase inhibitor, decreases the proliferation of RAW 264.7 macrophages and that another structurally unrelated inhibitor of PI3-kinase, LY294002, also inhibits the proliferation. These results indicate a possible involvement of PI3-kinase in RAW 264.7 macrophages growth regulation. Wortmannin stimulation of RAW 264.7 macrophages is followed by sustained expression of the mRNA of c-fos and a transient expression of the mRNA of c-jun. We also show that the wortmannin and LY294002 induce a cell cycle arrest in asynchronously growing cells leading to an inhibition of cell proliferation after 12 h of treatment. In addition, wortmannin or LY294002 inhibited the phorbol 12-myristate 13-acetate-induced macrophages proliferation potently. These results suggest that PI3-kinase plays an important role in growth regulation of RAW 264.7 macrophages and that protein kinase C is a down stream effector of PI3-kinase.

Circular muscle contraction, messenger signalling and localization of binding sites for neurokinin A in human sigmoid colon.

1. Neurokinin (NK)A is the endogenous ligand for the tachykinin NK2 receptor. In the present study, tachykinins and selective receptor agonists were tested as contractile agonists in human colon circular muscle and [125I]-NKA was used to localize binding sites in human colon. 2. In strips of circular muscle, removal of mucosa and submucosa significantly (P < 0.05) increased the potency and the maximum response achieved by NKA. 3. The rank order of potency of tachykinin and selective receptor agonists in contracting circular muscle strips was NKA > or = [Lys5,MeLeu9,Nle10]NKA(4-10) > or = neuropeptide (NP)gamma > or = [betaAla8]NKA(4-10) >> NKB > substance P (SP) >> senktide approximate to [Pro9]SP. 4. Specific binding sites for [125I]-NKA were densely localized over circular muscle and muscularis mucosae. Weak specific binding was seen on longitudinal muscle and taenia coli, whereas no binding sites were seen on mucosa, ganglia or blood vessels. 5. In circular muscle, the selective NK2 receptor agonist [LysS,MeLeu9,Nle10]NKA(4-10) produced weak increases (maximum 37%) in inositol monophosphate formation with a pD2 of 6.8+/-0.51 (n = 3). Carbachol (100 micromol/L) was also a weak stimulant (maximum 45%). These agonists were over 10-fold more efficacious in stimulation of inositol monophosphate in rat urinary bladder. 6. In conclusion, [125I]-NKA binding sites localized on human colon circular muscle were characterized as NK2 receptors. Functionally, the tachykinin NK2 receptor is mediating circular smooth muscle contraction. Although the human NK2 receptor is coupled to the phosphatidylinositol pathway, other second messenger mechanisms may also operate in this tissue.

TEP1, the yeast homolog of the human tumor suppressor gene PTEN/MMAC1/TEP1, is linked to the phosphatidylinositol pathway and plays a role in the developmental process of sporulation.

PTEN/MMAC1/TEP1 (PTEN, phosphatase deleted on chromosome ten; MMAC1, mutated in multiple advanced cancers; TEP1, tensin-like phosphatase) is a major human tumor suppressor gene whose suppressive activity operates on the phosphatidylinositol pathway. A single homologue of this gene, TEP1 (YNL128w), exists in the budding yeast Saccharomyces cerevisiae. Yeast strains deleted for TEP1 exhibit essentially no phenotype in haploids; however, diploids exhibit resistance to the phosphatidylinositol-3-phosphate kinase inhibitor wortmannin and to lithium ions. Although rates of cancer increase with age, neither tep1 haploids nor diploids have altered life spans. TEP1 RNA is present throughout the cell cycle, and levels are dramatically up-regulated during meiotic development. Although homozygous tep1 mutants initiate the meiotic program and form spores with wild-type kinetics, analysis of the spores produced in tep1 mutants indicates a specific defect in the trafficking or deposition of dityrosine, a major component of yeast spore walls, to the surface. Introduction of a common PTEN mutation found in human tumors into the analogous position in Tep1p produces a nonfunctional protein based on in vivo activity. These studies implicate Tep1p in a specific developmental trafficking or deposition event and suggest that Tep1p, like its mammalian counterpart, impinges on the phosphatidylinositol pathway.

Cutting edge: essential role of phospholipase C-gamma 2 in B cell development and function.

Cross-linking of the B cell Ag receptor (BCR) induces the tyrosine phosphorylation of multiple cellular substrates, including phospholipase C (PLC)-gamma 2, which is involved in the activation of the phosphatidylinositol pathway. To assess the importance of PLC-gamma 2 in murine lymphopoiesis, the PLC-gamma 2 gene was inducibly ablated by using IFN-regulated Cre recombinase. Mice with a neonatally induced loss of PLC-gamma 2 function displayed reduced numbers of mature conventional B cells and peritoneal B1 cells and defective responses in vitro to BCR stimulation and in vivo to immunization with thymus-independent type II Ags. In contrast, T cell development and TCR-mediated proliferation were normal. Taken together, PLC-gamma 2 is a critical component of BCR signaling pathways and is required to promote B cell development.

Increased Inhibitory Activity of Protein Kinase C on the Serotonin Transporter in OCD

Different observations show a reduced functionality of the serotonin (5-HT) transporter in obsessive-compulsive disorder (OCD) that might be due to a disturbance of its regulation at intracellular level. Protein kinase C (PKC) has been reported to provoke a decrease in the number of the 5-HT transporter proteins. Therefore, we investigated whether OCD patients differed from control subjects in the effect of PKC upon the 5-HT transporter, after stimulation of this enzyme with 4β-12-tetradecanoylphorbol 13-acetate (β-TPA). Fifteen patients affected by OCD, according to DSM-IV criteria, were compared with a similar group of healthy subjects. The determination of 5-HT uptake was carried out according to the method of Arora and Meltzer with slight modifications. At baseline, OCD patients showed a significant decrease in the maximal velocity (V_max) of 5-HT uptake, as compared with control subjects, with no change in the Michaelis-Menten constant (K_m). The activation of PKC with β-TPA provoked a significant decrease in V_max values in both groups, but the effect was significantly more robust in OCD patients who, in turn, also showed also an increase in K_m values. These findings could indicate the presence of hyperactivity of PKC in OCD that could be the result of increased activity of the phosphatidylinositol pathway. In addition, this suggests new potential therapeutic targets in OCD.

Expression of glypican-1, syndecan-1 and syndecan-4 mRNAs protein kinase C-regulated in rat immature Sertoli cells by semi-quantitative RT-PCR analysis

In seminiferous tubules, Sertoli cells provide structural and nutritional support for the developing germinal cells. Cell to cell signalization and cell adhesion require proteoglycans expressed at the cell membrane. A preliminary biochemical and structural approach indicated that cell surface proteoglycans are mostly heparan sulfate (HSPG) in immature rat Sertoli cells. The present study focused on the qualitative and quantitative expression of three membrane HSPG, syndecan-1, syndecan-4 and glypican-1 in Sertoli cells of 20-day-old rat. A semi-quantitative multiplex RT-PCR strategy was developed to appreciate the effect of PKC activation on the mRNA expression of the three HSPG. Our data show that the syndecan-1 and glypican-1 mRNA expression is increased by the phorbol myristate acetate (PMA) suggesting a regulation of their expression by the phosphatidyl inositol pathway, as previously hypothesized (Fagen et al., Biochim. Biophys. Acta, 1472 (1999) 250–261). In addition, a physiological effector of the PKC as ATP gave similar effects. Thus, this over-expression could be related with paracrine factors secreted by germ cells.

Pituitary Adenylate Cyclase-activating Polypeptides Directly Stimulate Sympathetic Neuron Neuropeptide Y Release through PAC1 Receptor Isoform Activation of Specific Intracellular Signaling Pathways

Pituitary adenylate cyclase-activating polypeptides (PACAP) have potent regulatory and neurotrophic activities on superior cervical ganglion (SCG) sympathetic neurons with pharmacological profiles consistent for the PACAP-selective PAC(1) receptor. Multiple PAC(1) receptor isoforms are suggested to determine differential peptide potency and receptor coupling to multiple intracellular signaling pathways. The current studies examined rat SCG PAC(1) receptor splice variant expression and coupling to intracellular signaling pathways mediating PACAP-stimulated peptide release. PAC(1) receptor mRNA was localized in over 90% of SCG neurons, which correlated with the cells expressing receptor protein. The neurons expressed the PAC(1)(short)HOP1 receptor but not VIP/PACAP-nonselective VPAC(1) receptors; low VPAC(2) receptor mRNA levels were restricted to ganglionic nonneuronal cells. PACAP27 and PACAP38 potently and efficaciously stimulated both cAMP and inositol phosphate production; inhibition of phospholipase C augmented PACAP-stimulated cAMP production, but inhibition of adenylyl cyclase did not alter stimulated inositol phosphate production. Phospholipase C inhibition blunted neuron peptide release, suggesting that the phosphatidylinositol pathway was a prominent component of the secretory response. These studies demonstrate preferential sympathetic neuron expression of PACAP-selective receptor variants contributing to regulation of autonomic function.

Involvement of phospholipid signal transduction pathways in morphine tolerance in mice.

1. Opioid tolerance involves an alteration in the activity of intracellular kinases such as cyclic AMP-dependent protein kinase (PKA). Drugs that inhibit PKA reverse morphine antinociceptive tolerance. The hypothesis was tested that phospholipid pathways are also altered in morphine tolerance. Inhibitors of the phosphatidylinositol and phosphatidylcholine pathways were injected i.c.v. in an attempt to acutely reverse morphine antinociceptive tolerance. 2. Seventy-two hours after implantation of placebo or 75 mg morphine pellets, mice injected i.c.v. with inhibitor drug were challenged with morphine s.c. for generation of dose-response curves in the tail-flick test. Placebo pellet-implanted mice received doses of inhibitor drug having no effect on morphine's potency, in order to test for tolerance reversal in morphine pellet-implanted mice. Injection of the phosphatidylinositol-specific phospholipase C inhibitor ET-18-OCH3 significantly reversed tolerance, indicating a potential role for inositol 1,4,5-trisphosphate (IP3) and protein kinase C (PKC) in tolerance. Alternatively, phosphatidylcholine-specific phospholipase C increases the production of diacylglycerol and activation of PKC, without concomitant production of IP3. D609, an inhibitor of phosphatidylserine-specific phospholipase C, also reversed tolerance. Heparin is an IP3 receptor antagonist. Injection of low molecular weight heparin also reversed tolerance. PKC was also examined with three structurally dissimilar inhibitors. Bisindolylmaleimide I, Go-7874, and sangivamycin significantly reversed tolerance. 3. Chronic opioid exposure leads to changes in phospholipid metabolism that have a direct role in maintaining a state of tolerance. Evidence is accumulating that opioid tolerance disrupts the homeostatic balance of several important signal transduction pathways.

Antigen receptor-mediated activation of extracellular related kinase (ERK) in B lymphocytes of teleost fishes

In mammalian B lymphocytes, engagement of the B cell antigen receptor (BCR) activates several parallel intracellular signaling pathways which ultimately lead to expression of differentiated functions such as cell proliferation and antibody production or to cellular apoptosis. BCR engagement stimulates the classical mitogen activated protein kinase (MAPK) pathway, also called the extracellular-related kinase (ERK) pathway, resulting in activation of the signature terminal enzyme in the pathway, MAPK (or ERK). BCR signaling also activates the phosphatidyl inositol pathway and its key enzyme protein kinase C (PKC). To investigate the ERK pathway in cells of the teleost immune system, peripheral blood leukocytes from red drum or channel catfish were treated with PKC activators or antibodies which crosslink the BCR. Proteins were identified in both red drum and catfish B cells that resembled mammalian ERKs in molecular weight and in their possessing a distinctive pTEpY dual phosphorylation site. BCR-mediated activation of these presumptive teleost ERKs depended in part (red drum) or in total (catfish) on PKC. To our knowledge this represents the first report of a functional MAPK kinase pathway in teleost fish.

Isozymes delta of phosphoinositide-specific phospholipase C.

Phospholipase C (PLC, EC 3.1.4.11) is the major starting point in the phosphatidylinositol pathway, which generates intracellular signals that regulate protein kinase C and intracellular calcium concentration. To date, three major types of phosphoinositide-specific PLC species named beta, gamma and delta, have been characterized. This article reviews recent studies on isozymes delta of PLC. Four such isozymes have been cloned and termed delta1-4. Their structural organization, regulation of activity and the interaction with membrane lipid are considered. The intracellular localization of delta isozymes and distribution in various tissues are presented. Attention is given to the pathological conditions in which an abnormal protein level of PLC delta or its activity have been observed.

Platelet membrane phospholipids in euthymic bipolar disorder patients: are they affected by lithium treatment?

Background: Abnormalities in cell membrane processes and intracellular signal transduction pathways may be implicated in the pathophysiology of bipolar disorder. In this study, we attempted to investigate, in euthymic bipolar patients: 1) in vivo signal transduction abnormalities of the phosphatidylinositol pathway in platelets; and 2) possible in vivo effects of lithium treatment on platelet membrane phospholipids. Methods: We determined the relative absorbances of eight individual classes of platelet membrane phospholipids, using two-dimensional thin-layer chromatography in high-performance plates, followed by scanning laser densitometry, in a group of 10 lithium-treated euthymic bipolar patients and 11 normal controls. Results: The mean relative absorbance of phosphatidylinositol-4,5-bisphosphate (PIP 2) was lower in the patient group (0.29 ± 0.08% vs. 0.39 ± 0.12%; t = 2.35, df = 19, p = .03); no significant differences between patients and controls were found for the other phospholipids. Conclusions: This study provides in vivo evidence that bipolar patients on lithium treatment exhibit a decreased relative amount of PIP 2 in the platelet cell membranes compared to normal controls.

Skittles, a Drosophila phosphatidylinositol 4-phosphate 5-kinase, is required for cell viability, germline development and bristle morphology, but not for neurotransmitter release.

The phosphatidylinositol pathway is implicated in the regulation of numerous cellular functions and responses to extracellular signals. An important branching point in the pathway is the phosphorylation of phosphatidylinositol 4-phosphate by the phosphatidylinositol 4-phosphate 5-kinase (PIP5K) to generate the second messenger phosphatidylinositol 4,5-bis-phosphate (PIP2). PIP5K and PIP2 have been implicated in signal transduction, cytoskeletal regulation, DNA synthesis, and vesicular trafficking. We have cloned and generated mutations in a Drosophila PIP5K type I (skittles). Our analysis indicates that skittles is required for cell viability, germline development, and the proper structural development of sensory bristles. Surprisingly, we found no evidence for PIP5KI involvement in neural secretion.

Vasopressin-induced calcium signaling in cultured cortical neurons

Earlier autoradiographic studies from our laboratory detected vasopressin recognition sites in the mammalian cerebral cortex [R.E. Brinton, K.W. Gee, J.K. Wamsley, T.P. Davis, H.I. Yamamura, Regional distribution of putative vasopressin receptors in rat brain and pituitary by quantitative autoradiography, Proc. Natl. Acad. Sci. U.S.A., 81 (1984) 7248–7252; C. Chen, R.D. Brinton, T.J. Shors, R.F. Thompson, Vasopressin induction of long-lasting potentiation of synaptic transmission in the dentate gyrus, Hippocampus, 3 (1993) 193–204]. More recently, we have detected mRNA for the V1a vasopressin receptors (V1aRs) in cultured cortical neurons [R.S. Yamazaki, Q. Chen, S.S. Schreiber, R.D. Brinton, V1a Vasopressin receptor mRNA expression in cultured neurons, astroglia, and oligodendroglia of rat cerebral cortex, Mol. Brain Res., 45 (1996) 138–140]. To determine whether these recognition sites are functional receptors, we have pursued the signal transduction mechanism associated with the V1a vasopressin receptor in enriched cultures of cortical neurons. Results of these studies demonstrate that exposure of cortical neurons to the selective V1 vasopressin receptor agonist, [Phe 2,Orn 8]-vasotocin, (V 1 agonist) induced a significant accumulation of [ 3 H] inositol-1-phosphate ( [ 3 H] IP 1). V 1 agonist-induced accumulation of [ 3 H] IP 1 was concentration dependent and exhibited a linear dose response curve. Time course analysis of V 1 agonist-induced accumulation of [ 3 H] IP 1 revealed a significant increase by 20 min which then decreased gradually over the remaining 60 min observation period. V 1 agonist-induced accumulation of [ 3 H] IP 1 was blocked by a selective V1a vasopressin receptor antagonist, (Phenylac 1, d-Tyr(Me) 2, Arg 6,8, Lys-NH 2 9)-vasopressin. Results of calcium fluorometry studies indicated that V 1 agonist exposure induced a marked and sustained rise in intracellular calcium which was abolished in the absence of extracellular calcium. The loss of the rise in intracellular calcium was not due to a failure to induce PIP 2 hydrolysis since activation of the phosphatidylinositol pathway occurred in the absence of extracellular calcium. V 1 agonist activation of calcium influx was then investigated. V 1 agonist-induced 45 Ca 2+ uptake was concentration dependent with a biphasic time course. Preincubation with the L-type calcium channel blocker, nifedipine, blocked V 1 agonist-induced calcium influx suggesting V 1 agonist-induced L-type calcium channel activation in cortical neurons. Furthermore, V 1 agonist-induced calcium influx was blocked by both bisindolyleimide I (PKC inhibitor) and U-73122 (PLC inhibitor) suggesting a modulation of V 1 agonist-induced L-type calcium channel activation by downstream components of the phosphatidylinositol signaling pathway such as protein kinase C. These results indicate that in cultured cortical neurons, V1a vasopressin receptor activation leads to induction of the phosphatidylinositol signaling pathway, influx of extracellular calcium via L-type calcium channel activation, and a rise in intracellular calcium which is dependent on V1a receptor activated influx of extracellular calcium. These data are the first to demonstrate an effector mechanism for the V 1 vasopressin receptor in the cerebral cortex and provide a potential biochemical mechanism that may underlie vasopressin enhancement of memory function.

Inhibition of the adenylyl cyclase and activation of the phosphatidylinositol pathway in oocytes through expression of serotonin receptors does not induce oocyte maturation

Inhibition of the adenylyl cyclase and activation of the phosphatidylinositol pathway in oocytes through expression of serotonin receptors does not induce oocyte maturation

The role of epidermal growth factor (EGF) and its receptor in mucosal protection, adaptation to injury, and ulcer healing: involvement of EGF-R signal transduction pathways.

Growth factors and their receptors are known to play important roles in normal cell proliferation, morphogenesis, tissue repair, and ulcer healing. Epidermal growth factor (EGF) inhibits acid secretion, exerts a trophic effect on gastroduodenal mucosa, protects gastric mucosa against injury, mediates mucosal adaptation, and accelerates gastroduodenal ulcer healing by stimulating cell migration and proliferation. EGF exerts its actions by binding to its receptor, EGF-R, a transmembrane protein tyrosine kinase, which triggers receptor dimerization, autophosphorylation, and recruitment of kinase substrates. These events result in Ras (GTP-binding protein) activation of the Ras/Raf/MAP kinase pathway, leading to phosphorylation of regulatory proteins and transcription factors and culminating in cell proliferation. Other pathways potentially activated by EGF include the phosphatidylinositol pathway and the JAK/STAT signaling pathway. Recent studies demonstrated that EGF-R-associated tyrosine kinase plays an essential role in regulating gastric mucosal cell proliferation after acute injury and further demonstrated activation of the EGF-R gene, EGF-R phosphorylation, and increased MAP kinase activity during early stages of experimental gastric ulcer healing. Finally, experimental data indicate that Helicobacter pylori vacuolating cytotoxin inhibits healing of experimental gastric ulcers, cell proliferation, binding of EGF to its receptor, EGF-induced EGF-R phosphorylation, and MAP kinase (ERK-2) activation. These H. pylori actions can explain its interference with the ulcer healing process.

Inhibition of the adenylyl cyclase and activation of the phosphatidylinositol pathway in oocytes through expression of serotonin receptors does not induce oocyte maturation

The identification of the initial signaling events induced by progesterone in Xenopus oocyte maturation was approached by expressing serotonin receptors and by using pharmacological agents. Suppression of phospholipase C (PLC) activity in oocytes by U-73122 or stimulation of oocyte adenylyl cyclase (ACase) by forskolin inhibited progesterone-induced reinitiation of meiotic cell division. Microinjection of cAMP-dependent protein kinase (PKA) pseudosubstrate, PKI, into oocytes--or pretreatment of oocytes with PKA inhibitor, H-89--did not induce oocyte maturation, but both treatments potentiated the rate of progesterone-induced germinal vesicle breakdown (GVBD). In addition, reduced PKA activity by H-89 reversed the inhibition of GVBD caused by U-73122. Expression and activation of the serotonin receptor type 1a or type 2c lowered intracellular cAMP level or mobilized Ins(1,4,5)P3, respectively. These oocytes, however, did not undergo maturation upon serotonin stimulation. Co-expression of these receptors also did not trigger maturation, but it significantly accelerated the rate of GVBD induced by progesterone. From these data, we conclude that (1) changes in levels of these second messengers may well be coupled with progesterone signaling; (2) an initial decrease in cAMP and production of Ins(1,4,5)P3/DG may not be absolute requisites for progesterone-induced meiotic maturation: (3) cross-talk mechanisms between adenylyl cyclase and phosphoinositide signal transduction pathways may exist in the process of progesterone-induced reinitiation of meiotic cell cycle.

β‐Adrenergic stimulation induces activation of protein kinase C and inositol 1,4,5‐trisphosphate increase in epidermis

Epidermal keratinocytes express beta 2-adrenergic receptors on the cell membrane. The binding of the agonists to the beta 2-adrenergic receptors regulates activation of adenylate cyclase. This transmembrane signaling system has been regarded to be one of the important pathways for the functions of keratinocytes. We previously reported that beta-adrenergic stimulation induced a transient increase of intracellular Ca2+ in normal human epidermal keratinocytes. Thus we investigated the effects of epinephrine on another transmembrane signaling system, the phosphatidyl-inositol signal transduction pathway in pig epidermis. Treatment of pig pure epidermis with epinephrine resulted in a transient increase in inositol 1,4,5-trisphosphate with a peak at 30 s. Epinephrine induced translocation of protein kinase C from cytosol to the membrane fraction. The activation of protein kinase C, translocation of protein kinase C from cytosol to the membrane fraction, was confirmed using the beta-adrenergic agonist isoproterenol. Moreover, the effect of epinephrine on the activation of protein kinase C was inhibited by preincubation with propranolol, a beta-adrenergic antagonist. The increase in inositol 1,4,5-trisphosphate and translocation of protein kinase C by epinephrine are consistent with the view that beta-adrenergic stimulation induces turnover of inositol phospholipid in pig epidermis.

Platelet membrane phosphatidylinositol-4,5-bisphosphate alterations in bipolar disorder — evidence from a single case study

Abnormalities in the cellular phosphatidylinositol (PI) pathway have been proposed to be implicated in the pathophysiology of bipolar disorder. A platelet model was used to study phosphatidylinositol-4,5-bisphosphate (PIP 2) membrane values in a bipolar disorder patient in different mood states, in a single case study. The patient was studied unmedicated, initially in the euthymic and later in the manic states, and subsequently on lithium after remission of manic symptoms. The relative percentage of PIP 2 in the platelet membranes increased with cycling from the euthymic into the manic state. After lithium treatment, PIP 2 decreased, and was similar to the euthymic state. This study further demonstrates the feasibility of this method, as well as its applicability to longitudinal studies in bipolar disorder, and suggests promising directions for future research in this area.

Endocrine Regulation of the Phosphatidylinositol Pathway in the Norway Lobster,Nephrops norvegicus,and the Shore Crab,Carcinus maenas

The present study examines the mode of action of eyestalk factors, in particular crustacean hyperglycaemic hormone (CHH), on known target tissues (muscle and hepatopancreas) in two decapod crustacean species,Nephrops norvegicusandCarcinus maenas.The possibility that receptors to CHH are coupled to an elevation of cytosolic Ca2+derived from intracellular stores via activation of the phosphatidylinositol pathway was investigated. Using an inositol 1,4,5-trisphosphate (InsP3)-specific competitive binding assay, measurable levels of InsP3were detected in hepatopancreas and muscle in bothN. norvegicusandC. maenas.Incubation of these tissues in the presence of sinus gland extracts (two sinus gland equivalents) consistently increased InsP3. In addition,CarcinusCHH (10 nM) increased InsP3levels inCarcinushepatopancreas and muscle. Incubation of hepatopancreas from both species in 10 mMlithium saline increased basal levels of InsP3, suggesting a significant turnover of phosphoinositides in this tissue.