Importance Of Inositol Research Articles

Inositol synthesis regulates the activation of GSK-3α in neuronal cells.

The synthesis of inositol provides precursors of inositol lipids and inositol phosphates that are pivotal for cell signaling. Mood stabilizers lithium and valproic acid, used for treating bipolar disorder, cause cellular inositol depletion, which has been proposed as a therapeutic mechanism of action of both drugs. Despite the importance of inositol, the requirement for inositol synthesis in neuronal cells is not well understood. Here, we examined inositol effects on proliferation of SK-N-SH neuroblastoma cells. The essential role of inositol synthesis in proliferation is underscored by the findings that exogenous inositol was dispensable for proliferation, and inhibition of inositol synthesis decreased proliferation. Interestingly, the inhibition of inositol synthesis by knocking down INO1, which encodes inositol-3-phosphate synthase, the rate-limiting enzyme of inositol synthesis, led to the inactivation of GSK-3α by increasing the inhibitory phosphorylation of this kinase. Similarly, the mood stabilizer valproic acid effected transient decreases in intracellular inositol, leading to inactivation of GSK-3α. As GSK-3 inhibition has been proposed as a likely therapeutic mechanism of action, the finding that inhibition of inositol synthesis results in the inactivation of GSK-3α suggests a unifying hypothesis for mechanism of mood-stabilizing drugs. Inositol is an essential metabolite that serves as a precursor for inositol lipids and inositol phosphates. We report that inhibition of the rate-limiting enzyme of inositol synthesis leads to the inactivation of glycogen synthase kinase (GSK) 3α by increasing inhibitory phosphorylation of this kinase. These findings have implications for the therapeutic mechanisms of mood stabilizers and suggest that inositol synthesis and GSK 3α activity are intrinsically related.

Distribution profile of inositol 1,4,5-trisphosphate receptor isoforms in adrenal chromaffin cells

Given the importance of inositol 1,4,5-trisphosphate receptor (IP 3R)/Ca 2+ channels in the control of intracellular Ca 2+ concentrations, we determined the relative concentrations of the IP 3R isoforms in subcellular organelles, based on serially sectioned electron micrographs. The endoplasmic reticulum (ER) was estimated to contain 15–20% of each of the three IP 3R isoforms while secretory granules contained 58–69%. The nucleus contained ∼15% each of IP 3R-1 and -2, but 25% of IP 3R-3, whereas the plasma membrane contained ∼1% or less of each. These suggested that secretory granules, the nucleus and ER are at the center of IP 3-dependent intracellular Ca 2+ control mechanisms in chromaffin cells.

Regulation of mouse egg activation: presence of ryanodine receptors and effects of microinjected ryanodine and cyclic ADP ribose on uninseminated and inseminated eggs.

Sperm-induced activation of mammalian eggs is associated with a transient increase in Ca2+ concentrations thought to be derived from inositol 1,4,5-trisphosphate-sensitive and -insensitive intracellular stores. Whereas the importance of inositol 1,4,5-trisphosphate-sensitive Ca2+ stores has been evaluated, the identity and role of inositol 1,4,5-trisphosphate-insensitive stores are poorly understood. To explore the role of the ryanodine-sensitive Ca2+ store, we first used reverse transcription-polymerase chain reaction to identify transcripts of the ryanodine receptor in eggs and determined that transcripts for the type 2 and 3 receptor were present. Immunoprecipitation of radioiodinated egg extracts with an antibody that recognizes both type 2 and 3 receptors detected specifically a band of Mr = 520,000. Immunolocalization of the receptor(s) using laser-scanning confocal microscopy revealed that the receptor(s) was uniformly distributed in the cortex of the germinal vesicle-intact oocyte, but became asymmetrically localized to the cortex in a region apposed to the meiotic spindle in the metaphase II-arrested egg; this asymmetrical localization developed by metaphase I. The role of the ryanodine receptor in mouse egg activation was examined by determining the effects of microinjected ryanodine or cyclic ADP ribose on endpoints of egg activation in either uninseminated or inseminated eggs. Ryanodine induced the conversion of the zona pellucida glycoprotein ZP2 to its postfertilization form ZP2f in a biphasic concentration-dependent manner; nanomolar concentrations stimulated this conversion, whereas micromolar concentrations had no stimulatory effect. Cyclic ADP ribose also promoted the ZP2 conversion, but with a hyperbolic concentration dependence. Neither of these compounds induced cell cycle resumption. Inhibiting the inositol 1,4,5-trisphosphate-sensitive Ca2+ store did not inhibit the ryanodine-induced ZP2 conversion and, reciprocally, inhibiting the ryanodine-sensitive Ca2+ store did not inhibit the inositol 1,4,5-trisphosphate-induced ZP2 conversion. Last, treatment of eggs under conditions that would block the release of Ca2+ from the ryanodine-sensitive store had no effect on any event of egg activation following fertilization. Results of these experiments suggest that although ryanodine receptors are present and functional, release of Ca2+ from this store is not essential for sperm-induced egg activation.

Importance of inositol (1,4,5)‐trisphosphate, intracellular Ca2+ release and myofilament Ca2+ sensitization in 5‐hydroxytryptamine‐evoked contraction of rabbit mesenteric artery

1. Small strips from third-order branches of rabbit mesenteric artery (approximately 150-200 microM wide) contracted in response to noradrenaline (10 microM) or 5-hydroxytryptamine (5-HT; 10 microM) in oxygenated Krebs solution containing 2.5 mM Ca2+. In a Ca(2+)-free mock intracellular solution (0 Ca2+ plus 0.2 mM EGTA), noradrenaline (10 microM) and caffeine (10 mM) induced only a single, transient contraction in artery strips, while 5-HT (10 microM) failed to induce any response. 2. In strips of mesenteric artery which had been permeabilized with Staphylococcus alpha-toxin and bathed in Ca(2+)-free mock intracellular solution, noradrenaline (10 microM), caffeine (10 mM) and D-myo-inositol (1,4,5)-trisphosphate (IP3, 100 microM), but not 5-HT (10 or 100 microM) induced a transient contraction. In contrast to the non-permeabilized strips, contractions to noradrenaline, caffeine and IP3 were restored by prior incubation (10 min) in solution containing 0.08 microM Ca2+. The contractions to noradrenaline and IP3 in permeabilized muscle strips required the presence of 100 microM guanosine 5'-triphosphate (GTP), although in the absence of Ca2+. GTP alone did not induce contraction. 3. Exposure of permeabilized mesenteric artery strips to IP3 significantly reduced the subsequent contractile responses to caffeine. Contractile responses to caffeine and IP3 were abolished by the Ca(2+)-ATPase inhibitor, thapsigargin (1 microM). 4. Ca2+ (0.1-10 microM) induced concentration-dependent contraction in permeabilized artery strips. In strips which were submaximally contracted with 0.5 microM Ca2+/100 microM GTP, the subsequent addition of 5-HT (10 microM) stimulated further contraction. The protein kinase C inhibitor, H-7 (1 microM) abolished the 5-HT/GTP-induced contraction, but did not alter the contraction to Ca2+. 5. In non-permeabilized, endothelium-denuded segments of rabbit mesenteric artery bathed in Ca2+-replete Krebs solution, noradrenaline (10 microM) stimulated a rapid, transient accumulation of IP3. 5-HT(100 microM) failed to stimulate IP3 accumulation during exposure periods of up to 5 min. 5-HT (100 microM)did stimulate IP3 accumulation if the external K+ concentration was raised (to around 25 mM). This concentration of K+ alone did not stimulate IP3 production and the 5-HT-stimulated IP3 accumulation in the presence of elevated extracellular [K+] was abolished by the alpha l-adrenoceptor antagonist, prazosin(O.1 microM).6. These results suggest that intracellular Ca2+ release does not play an important role in 5-HT-induced smooth muscle contraction in the rabbit mesenteric artery. This is despite the fact that a significant intracellular Ca2+ pool is present in these cells, which can be discharged by either noradrenaline or IP3.However, 5-HT did stimulate smooth muscle contraction in the presence of raised intracellular calcium,suggesting that a component of the contraction to 5-HT will reflect an increase in myofilament Ca2+sensitivity, possibly due to the activation of protein kinase C.

Morphogenetic Studies on Haworthia: Establishment of Tissue Culture and Control of Differentiation

Investigations were carried out on the in vitro morphogenetic responses of inflorescence segments and gynoecia of several species of Haworthia (Liliaceae). Morphogenetic responses of explants were not species specific. It was found that coconut milk was essential for the growth and differentiation of Haworthia tissue if White's basal medium was used. However, growth and differentiation could be supported by a modified Murashige and Skoog's medium, without any supplements. The investigations demonstrated’ the importance of inositol and ammonium nitrogen in the nutrition of Haworthia tissue cultures. A chemical control of callusing and shoot and root differentiation was obtained by providing appropriate amounts of auxin and cytokinin in the culture medium.

MORPHOGENETIC STUDIES ON HAWORTHIA: ESTABLISHMENT OF TISSUE CULTURE AND CONTROL OF DIFFERENTIATION

Investigations were carried out on the in vitro morphogenetic responses of inflorescence segments and gynoecia of several species of Haworthia (Liliaceae). Morphogenetic responses of explants were not species specific. It was found that coconut milk was essential for the growth and differentiation of Haworthia tissue if White's basal medium was used. However, growth and differentiation could be supported by a modified Murashige and Skoog's medium, without any supplements. The investigations demonstrated’ the importance of inositol and ammonium nitrogen in the nutrition of Haworthia tissue cultures. A chemical control of callusing and shoot and root differentiation was obtained by providing appropriate amounts of auxin and cytokinin in the culture medium.