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PubMed1991

Metabolism of Inositol(1,4,5)trisphosphate by a Soluble Enzyme Fraction from Pea (Pisum sativum) Roots.

Metabolism of the putative messenger molecule d-myo-inositol(1,4,5)trisphosphate [Ins(1,4,5)P(3)] in plant cells has been studied using a soluble fraction from pea (Pisum sativum) roots as enzyme source and [5-(32)P]Ins(1,4,5)P(3) and [2-(3)H]Ins(1,4,5)P(3) as tracers. Ins(1,4,5)P(3) was rapidly converted into both lower and higher inositol phosphates. The major dephosphorylation product was inositol(4,5)bisphosphate [Ins(4,5)P(2)] whereas inositol(1,4)bisphosphate [Ins(1,4)P(2)] was only present in very small quantities throughout a 15 minute incubation period. In addition to these compounds, small amounts of nine other metabolites were produced including inositol and inositol(1,4,5,X)P(4). Dephosphorylation of Ins(1,4,5)P(3) to Ins(4,5)P(2) was dependent on Ins(1,4,5)P(3) concentration and was partially inhibited by the phosphohydrolase inhibitors 2,3-diphosphoglycerate, glucose 6-phosphate, and p-nitrophenylphosphate. Conversion of Ins(1,4,5)P(3) to Ins(4,5)P(2) and Ins(1,4,5,X)P(4) was inhibited by 55 micromolar Ca(2+). This study demonstrates that enzymes are present in plant tissues which are capable of rapidly converting Ins(1,4,5)P(3) and that pathways of inositol phosphate metabolism exist which may prove to be unique to the plant kingdom.

Journal Article↗
PubMed2005

High-resolution structure of myo-inositol monophosphatase, the putative target of lithium therapy.

Inositol monophosphatase is a key enzyme of the phosphatidylinositol signalling pathway and the putative target of the mood-stabilizing drug lithium. The crystal structure of bovine inositol monophosphatase has been determined at 1.4 A resolution in complex with the physiological magnesium ion ligands. Three magnesium ions are octahedrally coordinated at the active site of each of the two subunits of the inositol monophosphatase dimer and a detailed three-metal mechanism is proposed. Ligands to the three metals include the side chains of Glu70, Asp90, Asp93 and Asp220, the backbone carbonyl group of Ile92 and several solvent molecules, including the proposed nucleophilic water molecule (W1) ligated by both Mg-1 and Mg-3. Modelling of the phosphate moiety of inositol monophosphate to superpose the axial phosphate O atoms onto three active-site water molecules orientates the phosphoester bond for in-line attack by the nucleophilic water which is activated by Thr95. Modelling of the pentacoordinate transition state suggests that the 6-OH group of the inositol moiety stabilizes the developing negative charge by hydrogen bonding to a phosphate O atom. Modelling of the post-reaction complex suggests a role for a second water molecule (W2) ligated by Mg-2 and Asp220 in protonating the departing inositolate. This second water molecule is absent in related structures in which lithium is bound at site 2, providing a rationale for enzyme inhibition by this simple monovalent cation. The higher resolution structural information on the active site of inositol monophosphatase will facilitate the design of substrate-based inhibitors and aid in the development of better therapeutic agents for bipolar disorder (manic depression).

Animals↗
PubMed1990

Inositol phospholipid turnover and intracellular Ca2+ responses to thyrotrophin-releasing hormone, gonadotrophin-releasing hormone and arginine vasopressin in pituitary corticotroph and somatotroph adenomas.

We have studied the inositol phospholipid turnover response to thyrotrophin-releasing hormone (TRH) gonadotrophin-releasing hormone (GnRH) and arginine vasopressin (AVP) in five corticotroph and six somatotroph pituitary adenomas. GnRH (100 nM) increased inositol phospholipid turnover in five of five somatotroph adenomas tested by an average of 36.4 +/- 9.4% (mean +/- SE). In a fifth, which was too small to allow inositol phospholipid turnover to be assessed, GnRH produced a rapid increase in mean intracellular calcium ion concentration. Only one of five corticotroph adenomas responded to GnRH with an increase in inositol phospholipid turnover of 19%. In contrast, all the somatotroph and corticotroph adenomas tested (four of four and five of five respectively) increased inositol phospholipid turnover in response to AVP (100 nM), by an average of 61 +/- 11.8% and 415 +/- 186% respectively. The finding of an inositol phospholipid or intracellular Ca2+ response to thyrotrophin-releasing hormone (TRH) (100 nM) in three of five somatotroph adenomas (Ca2+ increasing from 50 to 175 nM in one and inositol phospholipid turnover increasing by 172 +/- 1.9% and 49 +/- 5.2% in two) and to GnRH in all five somatotroph adenomas concurs with the common clinical finding of paradoxical growth hormone responses to these releasing factors in patients with acromegaly. The lack of such a response in three of the four corticotroph adenomas suggests that the appearance of GnRH and TRH receptors on adenomatous pituitary cells is not common to all cells.

Adenoma↗
PubMed1993

Pituitary adenomas with high and low basal inositol phospholipid turnover; the stimulatory effect of kinins and an association with interleukin-6 secretion.

OBJECTIVE: We examined basal inositol phospholipid turnover and the response to the kinin, kallidin, in human pituitary adenomas and determined whether or not there was an association between these parameters and interleukin (IL-6) secretion status by the tumours. DESIGN: Pituitary adenoma tissue was dispersed and cells were cultured in monolayer for 96 hours. The medium was then removed and assayed for IL-6 and anterior pituitary hormones. The cells were labelled with 3H-myoinositol for 24 hours and then incubated under basal conditions with kallidin and, in some cases, with TRH and GnRH for 60 minutes. Total inositol phosphate accumulation and pituitary hormone secretion were assessed. PATIENTS: Tissue was collected from 29 consecutive patients being treated surgically for pituitary adenomas. MEASUREMENTS: Total 3H-inositol phosphates, growth hormone, prolactin, LH, FSH, TSH and immunoreactive IL-6. RESULTS: Two groups of pituitary adenomas were identified, one with high and one with low basal inositol phospholipid turnover. Kallidin stimulated inositol phosphate accumulation in seven of the 29 adenomas studied. The kallidin-responsive adenomas were associated with high basal phosphoinositide turnover. All seven kallidin-responsive adenomas secreted IL-6. The adenomas studied with high basal inositol phosphate production were also responsive to TRH and in two tumours to GnRH. Kallidin stimulated GH release in one GH-secreting adenoma but had no effect on hormone secretion from any other tumour. CONCLUSION: Two groups of pituitary adenomas have been identified with high and low basal inositol phosphoinositide turnover. Phosphoinositide metabolism is readily stimulated by kallidin and TRH in adenomas with high but not low turnover. Kinin-responsive adenomas secreted IL-6 but IL-6 secretor status does not preclude that they will respond to kallidin.

Adenoma↗
PubMed1997

Inositol phospholipid 3-kinase is activated by cellular stress but is not required for the stress-induced activation of glucose transport in L6 rat skeletal muscle cells.

A characteristic response of cells subjected to a stress stimulus is a rapid activation of cellular glucose transport. The mechanisms governing this increase in glucose transport are poorly understood, but it has been suggested that the response may involve the intracellular-signaling components that also participate in the hormonal activation of glucose transport. In skeletal muscle and fat tissue, inositol phospholipid 3-kinase plays an integral role in the regulation of both basal and insulin-stimulated glucose transport. In this study, we have investigated whether inositol phospholipid 3-kinase is activated by chemical stress and, if so, whether it has a role to play in the stress-induced increase in glucose transport in L6 muscle cells. Furthermore, we have attempted to assess the basis by which inositol phospholipid 3-kinase may participate in the regulation of basal glucose transport. Acute exposure (30 min) of L6 muscle cells to 0.5 mM arsenite induced an 80% stimulation in glucose transport. This activation was due to a rise in the number of cell-surface glucose transporters, based on an increase in the Vmax of glucose transport and the observation that arsenite increases the plasma membrane content of GLUT1 and GLUT4 glucose transporters by 95% and 60%, respectively, from an intracellular compartment. Arsenite induced rapid activation (< 2 min) of inositol phospholipid 3-kinase with an approximately fourfold increase in phosphatidylinositol 3,4,5-trisphosphate (PtdIns3,4,5P3). In contrast, phosphatidylinositol 3-phosphate (PtdIns3P) levels were unaffected. Prior treatment of L6 cells with 100 nM wortmannin suppressed the arsenite-induced increase in PtdIns3,4,5P3 and reduced the cellular content of PtdIns3P by 50%. Under these conditions however, wortmannin failed to prevent the stress-induced activation of glucose transport, but suppressed basal glucose transport by 60% with an IC50 of about 10 nM. In the absence of arsenite, wortmannin caused a dose-dependent inhibition in the cellular levels of PtdIns3P and PtdIns3,4,5P3 with IC50 values of about 10 nM and 100 nM, respectively. In summary, the present results demonstrate that chemical stress activates inositol phospholipid 3-kinase and glucose transport in L6 muscle cells, but unlike the hormonal responses of these cells the activation of inositol phospholipid 3-kinase is not responsible for the stress-induced increase in glucose transport. This implies that stress-induced and hormonal stimulated increases in PtdIns3,4,5P3 levels are functionally distinct. By contrast, the maintenance of PtdIns3P levels, presumably involving a PtdIns-specific, wortmannin-sensitive inositol phospholipid 3-kinase may be required to support basal glucose transport.

Androstadienes↗
PubMed1988

Neurokinin3-receptors are linked to inositol phospholipid hydrolysis in the guinea-pig ileum longitudinal muscle-myenteric plexus preparation.

1. Tachykinin-stimulated inositol phospholipid hydrolysis was examined in slices of longitudinal muscle from guinea-pig ileum. 2. Substance P, neurokinin A and neurokinin B induced a concentration-dependent accumulation of total [3H]-inositol phosphates in the presence of 12 mM lithium with similar maximal responses and EC50 values. 3. The selective NK1-receptor agonist, substance P methyl ester, and the selective NK3-receptor agonist succ-[Asp6, MePhe8]-SP(6-11) (senktide) also stimulated [3H]-inositol phosphate formation with maximum responses of 50.69 +/- 0.96 and 45.64 +/- 1.17% relative to 10 microM substance P, respectively. Substance P methyl ester was approximately equipotent with substance P, whereas senktide was approximately 100 times more potent. 4. When added together, maximally effective concentrations of substance P methyl ester and senktide gave responses that were fully additive. In contrast, responses to substance P and neurokinin B were not additive. 5. The stimulation of [3H]-inositol phosphate formation by substance P, neurokinin B and senktide was not affected by atropine (2 microM) or tetrodotoxin (TTX, 0.3 microM). 6. The contractile effect of senktide was inhibited completely by TTX and partially blocked by atropine. Contractions induced by substance P methyl ester were not changed in the presence of TTX or atropine. 7. [D-Pro4, D-Trp7,9,10]-SP(4-11) competitively antagonized the action of substance P methyl ester on inositol phospholipid hydrolysis and contraction, but had no significant effect on senktide-induced inositol phospholipid breakdown or contraction. 8. These results suggest that NK3-receptors in the guinea-pig ileum are coupled to inositol phospholipid hydrolysis.

Animals↗
PubMed1994

The mechanism of muscarinic agonist-stimulated inositol phosphate formation in permeabilized ileal smooth muscle.

Muscarinic agonists and guanylyl-5'-imidodiphosphate (Gpp(NH)p) stimulated formation of inositol phosphates in permeabilized longitudinal smooth muscle of guinea pig ileum. Gpp(NH)p markedly potentiated the formation of inositol bisphosphate (IP2) and inositol trisphosphate (IP3) stimulated by carbachol, but increased inositol monophosphate formation (IP1) only slightly. Gpp(NH)p enhanced the formation of IP2 + IP3 induced by either acetylcholine or carbachol about fourfold in a synergistic manner, but enhanced the effects of oxotremorine and pilocarpine less than twofold in an additive manner. Elevation of Ca2+ concentration resulted in increases of the inositol phosphate levels stimulated by both carbachol and Gpp(NH)p. The optimal concentration of Ca2+ for carbachol-stimulated formations of IP2 + IP3 was shifted to a lower Ca2+ concentration in the presence of Gpp(NH)p. These findings suggest that muscarinic receptor-stimulated polyphosphoinositide hydrolysis in ileal smooth muscle results in inositol polyphosphate formation via GTP binding protein (G-protein). The muscarinic receptor-activated G-protein decreases the Ca2+ requirement of polyphosphoinositide hydrolysis. Muscarinic agonists stimulate inositol polyphosphate formation by interaction of the G-protein activation of a phosphoinositide specific phospholipase C with Ca2+ influx.

Acetylcholine↗
PubMed1994

Inositol polyphosphate 1-phosphatase is present in the nucleus and inhibits DNA synthesis.

Inositol polyphosphate 1-phosphatase, an enzyme of the phosphatidylinositol signaling pathway, hydrolyzes the 1-phosphate from inositol 1,4-bisphosphate and inositol 1,3,4-trisphosphate. We have used indirect immunofluorescence microscopy, Western blot analysis, and enzyme assays to determine the cellular localization of the enzyme. We find that the enzyme is present, but not exclusively, in the nucleus of Madin-Darby bovine kidney cells, and also in COS-7 and HeLa cells that were transiently transfected with a cDNA encoding bovine inositol polyphosphate 1-phosphatase. DNA synthesis, as measured in COS-7 and HeLa cells transiently over-expressing enzyme, was reduced 50% in cells transfected with wild-type enzyme compared with nontransfected cells or cells transfected with an inactive mutant form of the enzyme. These data demonstrate that this response is mediated by one of the substrates or products of inositol polyphosphate 1-phosphatase. We propose that overexpressed inositol polyphosphate 1-phosphatase degrades a stimulatory inositol phosphate(s) and thereby inhibits DNA synthesis.

Amino Acid Sequence↗
PubMedDate not supplied

TLC characterization of small unilamellar liposomes containing D-myo-inositol derivatives.

The thin-layer chromatographic (TLC) behaviour of small unilamellar liposomes containing inositol phosphates (IPs) was studied. The vesicles contained different concentrations of D-myo-inositol 1,4,5-triphosphate (IP3), D-myo-inositol 1,2,6-triphosphate (alpha-trinositol, PP 56, a novel Perstorp Pharma derivative), D-myo-inositol 1,3,4,5-tetraphosphate (IP4), D-myo-inositol 1,3,4,5,6-pentakisphosphate (IP5) and D-myo-inositol 1,2,3,4,5,6-hexakisphosphate (IP6). Migration of all liposome batches was compared to that of control liposomes (multilamellar and small unilamellar, both containing only triple-distilled water), and to that of free phosphatidylcholine (PC). The same amount of lipid was used in all situations. Thin-layer chromatography was performed with silica gel as adsorbent. The developing solvent was an n-buthanol:ethanol:water mixture in a 4:3:3 volume ratio. At doses higher than 10(-2) M liposomes containing alpha-trinositol and IP6 had a different migration than PC, MLV or SUV as well as all batches of liposomes. Physiological studies (using as model endothelized rat aorta rings) proved that in this situation they had no effects.

Animals↗
PubMedDate not supplied

TLC characterization of liposomes containing D-myo-inositol derivatives.

The thin-layer chromatographic (TLC) behaviour of liposomes containing inositol phosphates (IPs) was studied. The liposomes contained different concentrations of D-myo-inositol 1,4,5k-trisphosphate (IP3), D-myo-inositol 1,2,6-trisphosphate (alpha-trinositol, PP 56, a novel Perstorp Pharma derivative), D-myo-inositol 1,3,4,5-tetrakisphosphate (IP4), D-myo-inositol 1,3,4,5,6-pentakisphosphate (IP5) and D-myo-inositol 1,2,3,4,5,6-hexakisphosphate (IP6). Migration of all liposome batches was compared to that of control liposomes (containing only triple distilled water), and to that of free phosphatidylcholine (PC); the same amount of lipid was used in all situations. Thin-layer chromatography was performed on silica gel as adsorbent. As solvent we used an n-buthanol:ethanol:water mixture in a 4:3:3 volume ratio. Significant differences were found between PC and all liposome batches, as well as between control liposomes and the ones containing IP3, alpha-trinositol, IP4, or IP5, in various concentrations. Liposomes containing IP6 migrate completely differently compared not only to phosphatidylcholine and control liposomes, but also to the ones containing other IPs ( < 10(-3) M). Unlike the other IPs studied, liposome-entrapped IP6 elicits dose-dependent contractions of the isolated rat aorta. This suggests that liposomes loaded with IP6 undergo, during or after their preparation, physico-chemical alterations that eventually change their drug-delivery capacity.

Animals↗
PubMed1988

Characterization of a mutation that causes overproduction of inositol in Neurospora crassa.

Slow-growing (inl+/-) spontaneous mutants have been isolated from an inositol requiring (inl) strain of Neurospora crassa that produces defective myo-inositol-1-phosphate synthase (MIPS), the enzyme responsible for the production of inositol-1-phosphate from glucose-6-phosphate. The defective enzyme has some residual activity. In the inl+/- strain the synthesis of the defective enzyme is enhanced, which enables the strain to grow slowly on minimal medium. The mutation (opi1) responsible for the partial inositol independence segregates independently from the inositol locus, and suppresses the inositolless character by overproduction of defective MIPS. opi1 acting upon the wild type (inl+) allele increases MIPS production and causes inositol excretion.

Genes↗
PubMed1986

Determination of basal and stimulated levels of inositol triphosphate in [32P]orthophosphate-labeled platelets.

Previous studies indicated that thrombin-stimulation of platelets prelabeled with [3H]inositol or [32P]orthophosphate results in an increase of radioactive inositol triphosphate, a substance thought to modulate the levels of free intracellular calcium. In the present study, we improved the method of resolution of inositol triphosphate from other compounds that are also labeled with [32P]orthophosphate using a combination of enzyme treatment and electrophoresis. We have further demonstrated that the specific activities of metabolic ATP and phosphatidylinositol diphosphate (the precursor of inositol triphosphate) are identical in [32P]orthophosphate-labeled platelets. It follows that the amount of inositol triphosphate is proportional to its radioactivity in the metabolic compartment of the cells. Using this protocol, the concentration of inositol triphosphate in resting and thrombin-stimulated platelets were determined to be 1-4 and 10-30 pmol/10(8) cells, respectively.

Adenosine Triphosphate↗
PubMed1987

Inositol 1,2-cyclic 4,5-trisphosphate is formed in the rat parotid gland on muscarinic stimulation.

Hawkins et al. [Hawkins, P.T., Berrie, C.P., Morris, A.J., and Downes, C.P. (1987) Biochem J. 243, 211-218] were unable to find any formation of inositol 1,2-cyclic 4,5-trisphosphate on muscarinic stimulation of rat parotid slices, contrary to what has been found in mouse pancreas and in platelets. We have repeated the studies of Hawkins et al. using [3H]inositol-prelabelled rat parotid minilobules and our improved HPLC method for clearly separating the three inositol trisphosphates. Substantial amounts of inositol 1,2-cyclic 4,5-trisphosphate formed on muscarinic stimulation of rat parotid minilobules, amounting to 5% of inositol 1,4,5-trisphosphate at 10 sec and one third of inositol 1,4,5-trisphosphate at 5 min.

Animals↗
PubMed1987

Stimulations of arachidonate release and inositol-1,4,5-triphosphate formation are mediated by distinct G-proteins in human platelets.

Addition of fluoroaluminate to human platelet suspension stimulated thromboxane synthesis and inositol-1,4,5-triphosphate formation in a time and dose dependent manner. Neomycin inhibited markedly fluoroaluminate induced inositol-1,4,5-triphosphate formation without significantly affecting thromboxane synthesis. Preincubation of platelets with PGE1, also inhibited significantly inositol-1,4,5-triphosphate formation with modest reduction of thromboxane synthesis. On the contrary, pretreatment of platelets with pertussis toxin inhibited fluoroaluminate stimulated thromboxane synthesis without affecting inositol-1,4,5-triphosphate formation. Similarly, preincubation of platelets with phorbol ester, PMA, inhibited markedly thromboxane synthesis with modest reduction of inositol-1,4,5-triphosphate formation. These results indicate that inositol-1,4,5-triphosphate formation and arachidonate release and thromboxane synthesis are controlled separately and are mediated by different G-proteins which are coupled to phospholipase C and phospholipase A2 respectively in platelets.

Aluminum↗
PubMed1987

Production of inositol pentakisphosphate in a human T lymphocyte cell line.

The human T lymphocyte cell line, Jurkat, produced five distinct water soluble, inositol-containing compounds following a period of labeling with 3H-myo-inositol and several hours of incubation in non-radioactive complete medium. The less polar four peaks had been previously shown to be inositol phosphates, InsP through InsP4. Here, we demonstrate that the prominent fifth, very polar, peak was inositol pentakisphosphate, InsP5. The pattern of incorporation of 3H-myo-inositol into InsP5 differed from that of incorporation into other inositol phosphates. InsP5, unlike the second messengers, InsP3 and InsP4, was not increased by perturbation of the T cell receptor/T3 complex.

Humans↗
PubMed1990

Agonist-mediated formation of inositol monophosphate isomers in rat cortical prisms.

The carbachol and adrenaline-mediated accumulation of inositol monophosphate isomers in rat cortical prisms has been studied using a commonly employed experimental protocol involving preincubation with myo-[2-3H]-inositol and subsequent incubation with agonists in the presence of 10 mM LiCl. Inositol phosphate isomers have been analysed by HPLC and identified by comparison of their elution characteristics with those of commercially available standards and the degradation products of authentic Ins 1,3,4-P3 and Ins 1,4,5-P3. Incubation of prelabelled cortical prisms for 1 hr with 10 mM LiCl alone gives rise to accumulation of radioactivity in two inositol monophosphate peaks which co-elute with Ins 1-P and Ins 4-P and one major bisphosphate peak which co-migrates with Ins 1,4-P2. Most of the monophosphate radioactivity is recovered in the Ins 4-P peak (Ins 1-P/Ins 4-P labelling ratio 0.68). Both carbachol and adrenaline produce dose-dependent increases in the labelling of Ins 1-P and Ins 4-P which are antagonized by atropine and prazosin respectively. However, carbachol produces a larger stimulation of accumulation of both monophosphates and also gives rise to a larger selective increase in the accumulation of Ins 1-P (Ins 1-P/4-P labelling ratio 1.40 in the presence of 1 mM carbachol, 0.98 in the presence of 1 mM adrenaline). Kinetic studies of the carbachol-stimulated increases in inositol mono- and bisphosphate labelling have revealed that, in the early period following carbachol addition (0-5 min), Ins 4-P and Ins 1,4-P2 are labelled more rapidly than Ins 1-P, whereas the reverse is true at later periods (15-60 min) of the incubations. These observations, coupled with the low levels of labelling of the major Ins 1,3,4-P3 breakdown products (Ins 1,3-P2 and Ins 3,4-P2) compared with that of Ins 1,4-P2, suggest that large-scale production of Ins 1-P is a comparatively late feature of carbachol-mediated inositol phospholipid metabolism and that, if the Ins 1-P is derived from breakdown of Ins 1,3,4,5-P4 via Ins 1,3,4-P3, the turnover of Ins 1,3-P2 + Ins 3,4-P2 must be approximately one order of magnitude greater than that of the Ins 4-P precursor, Ins 1,4-P2.

Animals↗
PubMed1992

Synthesis of racemic 5-phosphonate analogues of myo-inositol 1,4,5-tris- and 1,3,4,5-tetrakis-phosphate.

(+/-)-2,3,6-Tri-O-benzyl-5-O-p-methoxybenzyl-myo-inositol and (+/-)-2,6-di-O-benzyl-5-O-p-methoxy-benzyl-myo-inositol, accessible readily from (+/-)-3,6-di-O-allyl-1,2-O-cyclohexylidene-myo-inositol, were phosphitylated with dibenzyl N,N-di-isopropylphosphoramidite, and the resulting phosphite triesters were oxidised with tert-butyl hydroperoxide to give the corresponding fully protected myo-inositol 1,4-bis- (12) and 1,3,4-tris-phosphate (13) derivatives. Cleavage of the p-methoxybenzyl group from 12 and 13, phosphonylation with bis[6-(trifluoromethyl)benzotriazol-1-yl] methylphosphonate or (difluoromethyl)phosphonic di(1,2,4-triazolide), followed by treatment in situ with benzyl alcohol, and then hydrogenolysis of the benzyl groups gave the 5-methylphosphonate and 5-[(difluoromethyl)phosphonate] analogues of myo-inositol 1,4,5-tris- and 1,3,4,5-tetrakis-phosphate. The 5-methylphosphonate analogue of myo-inositol 1,4,5-trisphosphate acted as a calcium antagonist in permeabilized human platelets.

Blood Platelets↗
PubMed1990

Rapid increase in inositol pentakisphosphate accumulation by nicotine in cultured adrenal chromaffin cells.

When [3H]inositol-prelabeled cultured bovine adrenal chromaffin cells were stimulated with nicotine (10 microM), a large and transient increase in [3H]inositol pentakisphosphate (InsP5) accumulation was observed. The accumulation reached the maximum level at 15 s, then declined to the basal level at 2 min. Nicotine also induced [3H]inositol tetrakisphosphate (InsP4) and [3H]inositol hexakisphosphate (InsP6) accumulation with a slower time course and a lesser magnitude than [3H]InsP5. The peaks of [3H]InsP4, [3H]InsP5 and [3H]InsP6 coincided with those of 32P radioactivity, when cells were doubly labeled with [3H]inositol and inorganic 32P. These results suggest that inositol pentakisphosphate is rapidly increased by nicotine, a cholinergic agonist, in cultured adrenal chromaffin cells.

Adrenal Medulla↗