Injection Of IP3 Research Articles

Anti-inflammatory effect of omega-7 against doxorubicin-induced cardiotoxicity in male rats: An observational study

Background: Doxorubicin is a crucial anticancer medication, however, cardiotoxicity is a severe adverse effect of doxorubicin therapy. Various mechanisms, including inflammation, have been postulated to account for this negative effect. The omega-7 fatty acid is a polyunsaturated fatty acid with anti-inflammatory and antioxidant properties. Therefore, the study's objective was to see whether omega-7 had any possible protective benefits against doxorubicin-induced cardiotoxicity in male rats. Methods: 28 male Wister rats were split into four groups (seven per group). Group 1 (negative control): healthy animals received normal saline orally as the vehicle for eight successive days and were sacrificed on day nine. Group 2 (positive control): animals that received a single dose of doxorubicin hydrochloride (IP 15mg/kg) were sacrificed the next day. Group 3: the animals were administered omega-7 orally at a 100 mg/kg/day dose for eight days. A single injection of doxorubicin IP (15 mg/kg) was given on day nine. The animals were sacrificed on day 10. Group 4: the animal was administered omega-7 orally at a 300 mg/kg/day dose for eight days. A single injection of doxorubicin IP (15 mg/kg) was given on day nine. The animals were sacrificed on day 10. Serum was collected and used to measure lactate dehydrogenase, creatinine kinase-MB, tumor necrosis factor-alpha, interleukin-6, and interleukin-1beta. Results: Lactate dehydrogenase and creatinine kinase-MB levels in group 3 (100mg/kg) were significantly lower than in group 2 (p>0.05) and significantly lower in group 4 (300mg/kg) than in group 2. Tumor necrosis factor-alpha, interleukin-6, and interleukin-1beta levels were considerably lower in the omega-7-treated groups (100 and 300mg/kg) than in the positive control group (p<0.05). Conclusion: Through a mechanism involving the reduction of inflammation, omega-7 may preserve the cardiac tissue against doxorubicin-induced damage.

The positive effect of metformin and metronidazole on the diabetic rats experimentally

Diabetes mellitus is considering most serious disease of endocrine, it affecting large number of people in worldwide. This study was performed to insured the effect of combination of metformin and metronidazole on disorder in metabolic that concomitant with injection of alloxan IP induced diabetes in rats. In this study forty male rats: divided into four groups including control group G1, alloxn group (150 mg/kg single dose) G2, alloxn group orally treated with metformin (150mg/kg/BW) G3, and alloxn group orally treated with metformin (150mg/kg/BW) and metronidazole (500mg/kg/BW) G4. The experiment last for 14 days. The result shows marked increase in MDA, glucose and also in liver enzymes, lipid profiles and even observed disorder in kidney function test by increased in the creatinine, urea, and uric acid levels. In addition to study the histological changes in diabetic liver of rats characterized by kupffer cells activation, dilation and congestion of central vein and hepatic sinusoids. Administration of metformin and combination of metformin and metronidazole, result in significant reduction return abnormal parameters to the normal values. Also correct the abnormal histological changes of liver.

Focal activation of cells by plasmon resonance assisted optical injection of signaling molecules.

Experimental methods for single cell intracellular delivery are essential for probing cell signaling dynamics within complex cellular networks, such as those making up the tumor microenvironment. Here, we show a quantitative and general method of interrogation of signaling pathways. We applied highly focused near-infrared laser light to optically inject gold-coated liposomes encapsulating bioactive molecules into single cells for focal activation of cell signaling. For this demonstration, we encapsulated either inositol trisphosphate (IP3), an endogenous cell signaling second messenger, or adenophostin A (AdA), a potent analogue of IP, within 100 nm gold-coated liposomes, and injected these gold-coated liposomes and their contents into the cytosol of single ovarian carcinoma cells to initiate calcium (Ca2+) release from intracellular stores. Upon optical injection of IP3 or AdA at doses above the activation threshold, we observed increases in cytosolic Ca2+ concentration within the injected cell initiating the propagation of a Ca2+ wave throughout nearby cells. As confirmed by octanol-induced inhibition, the intercellular Ca2+ wave traveled via gap junctions. Optical injection of gold-coated liposomes represents a quantitative method of focal activation of signaling cascades of broad interest in biomedical research.

Polyspermy block in jellyfish eggs: Collaborative controls by Ca2+ and MAPK

Jellyfish eggs neither undergo apparent cortical reaction nor show any significant change in the membrane potential at fertilization, but nevertheless show monospermy. Utilizing the perfectly transparent eggs of the hydrozoan jellyfish Cytaeis uchidae, here we show that the polyspermy block is accomplished via a novel mechanism: a collaboration between Ca2+ and mitogen-activated protein kinase (MAPK). In Cytaeis, adhesion of a sperm to the animal pole surface of an egg was immediately followed by sperm–egg fusion and initiation of an intracellular Ca2+ rise from this site. The elevated Ca2+ levels lasted for several minutes following the sperm–egg fusion. The Ca2+ rise proved to be necessary and sufficient for a polyspermy block, as inhibiting a Ca2+ rise with EGTA promoted polyspermy, and conversely, triggering a Ca2+ rise by inositol 1,4,5-trisphosphate (IP3) or excess K+ immediately abolished the egg’s capacity for sperm–egg fusion. A Ca2+ rise at fertilization or by artificial stimulations evoked dephosphorylation of MAPK in eggs. The eggs in which phosphorylated MAPK was maintained by injection of mRNA for MAPK kinase kinase (Mos), like intact eggs, exhibited a Ca2+ rise at fertilization or by IP3 injection, and shut down the subsequent sperm–egg fusion. However, the Mos-expressing eggs became capable of accepting sperm following the arrest of Ca2+ rise. In contrast, addition of inhibitors of MAPK kinase (MEK) to unfertilized eggs caused MAPK dephosphorylation without elevating Ca2+ levels, and prevented sperm–egg fusion. Rephosphorylation of MAPK by injecting Mos mRNA after fertilization recovered sperm attraction, which is known to be another MAPK-dependent event, but did not permit subsequent sperm–egg fusion. Thus, it is possible that MAPK dephosphorylation irreversibly blocks sperm–egg fusion and reversibly suppresses sperm attraction. Collectively, our data suggest that both the fast and late mechanisms dependent on Ca2+ and MAPK, respectively, ensure a polyspermy block in jellyfish eggs.

Type 1 Inositol (1,4,5)-Trisphosphate Receptor Activates Ryanodine Receptor 1 to Mediate Calcium Spark Signaling in Adult Mammalian Skeletal Muscle

Functional coupling between inositol (1,4,5)-trisphosphate receptor (IP(3)R) and ryanodine receptor (RyR) represents a critical component of intracellular Ca(2+) signaling in many excitable cells; however, the role of this mechanism in skeletal muscle remains elusive. In skeletal muscle, RyR-mediated Ca(2+) sparks are suppressed in resting conditions, whereas application of transient osmotic stress can trigger activation of Ca(2+) sparks that are restricted to the periphery of the fiber. Here we show that onset of these spatially confined Ca(2+) sparks involves interaction between activation of IP(3)R and RyR near the sarcolemmal membrane. Pharmacological prevention of IP(3) production or inhibition of IP(3)R channel activity abolishes stress-induced Ca(2+) sparks in skeletal muscle. Although genetic ablation of the type 2 IP(3)R does not appear to affect Ca(2+) sparks in skeletal muscle, specific silencing of the type 1 IP(3)R leads to ablation of stress-induced Ca(2+) sparks. Our data indicate that membrane-delimited signaling involving cross-talk between IP(3)R1 and RyR1 contributes to Ca(2+) spark activation in skeletal muscle.

PYK2: A calcium-sensitive protein tyrosine kinase activated in response to fertilization of the zebrafish oocyte

Fertilization begins with binding and fusion of a sperm with the oocyte, a process that triggers a high amplitude calcium transient which propagates through the oocyte and stimulates a series of preprogrammed signal transduction events critical for zygote development. Identification of the pathways downstream of this calcium transient remains an important step in understanding the basis of zygote quality. The present study demonstrates that the calcium-calmodulin sensitive protein tyrosine kinase PYK2 is a target of the fertilization-induced calcium transient in the zebrafish oocyte and that it plays an important role in actin-mediated events critical for sperm incorporation. At fertilization, PYK2 was activated initially at the site of sperm–oocyte interaction and was closely associated with actin filaments forming the fertilization cone. Later PYK2 activation was evident throughout the entire oocyte cortex, however activation was most intense over the animal hemisphere. Fertilization-induced PYK2 activation could be blocked by suppressing calcium transients in the ooplasm via injection of BAPTA as a calcium chelator. PYK2 activation could be artificially induced in unfertilized oocytes by injection of IP3 at concentrations sufficient to induce calcium release. Functionally, suppression of PYK2 activity by chemical inhibition or by injection of a dominant-negative construct encoding the N-terminal ERM domain of PKY2 inhibited formation of an organized fertilization cone and reduced the frequency of successful sperm incorporation. Together, the above findings support a model in which PYK2 responds to the fertilization-induced calcium transient by promoting reorganization of the cortical actin cytoskeleton to form the fertilization cone.

No evidence for inositol 1,4,5-trisphosphate–dependent Ca2+ release in isolated fibers of adult mouse skeletal muscle

The presence and role of functional inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) in adult skeletal muscle are controversial. The current consensus is that, in adult striated muscle, the relative amount of IP3Rs is too low and the kinetics of Ca2+ release from IP3R is too slow compared with ryanodine receptors to contribute to the Ca2+ transient during excitation–contraction coupling. However, it has been suggested that IP3-dependent Ca2+ release may be involved in signaling cascades leading to regulation of muscle gene expression. We have reinvestigated IP3-dependent Ca2+ release in isolated flexor digitorum brevis (FDB) muscle fibers from adult mice. Although Ca2+ transients were readily induced in cultured C2C12 muscle cells by (a) UTP stimulation, (b) direct injection of IP3, or (c) photolysis of membrane-permeant caged IP3, no statistically significant change in calcium signal was detected in adult FDB fibers. We conclude that the IP3–IP3R system does not appear to affect global calcium levels in adult mouse skeletal muscle.

IP3-mediated octopamine-induced synaptic enhancement of crayfish LG neurons

The biogenic amines, octopamine and serotonin, modulate the synaptic activity of the lateral giant interneuron (LG) circuitry of the crayfish escape behavior. Bath application of both octopamine and serotonin enhances the synaptic responses of LG to sensory stimulation. We have shown previously (Araki et al. J Neurophysiol 94:2644-2652, 2005) that a serotonin-induced enhancement of the LG response was mediated by an increase in cAMP levels following activation of adenylate cyclase; however, octopamine acts independently. Here, we clarify how octopamine enhances the LG response during sensory stimulation using physiological and pharmacological analyses. When phospholipase C inhibitor U-73122 was directly injected into the LG before biogenic amine application, it abolished the enhancing effect of octopamine on direct sensory input to the LG, but did not block indirect input via sensory interneurons or the effect of serotonin. Direct injection of IP(3), and its analogue adenophostin A, into the LG increased the synaptic response of the LG to sensory stimulation. Thus, IP(3) mediates octopamine-induced synaptic enhancement of the LG, but serotonin acts independently. These results indicate that both octopamine and serotonin enhance the synaptic responses of the LG to sensory stimulation, but that they activate two different signaling cascades in the LG.

Intracellular Cannabinoid Type 1 (CB1) Receptors Are Activated by Anandamide

Recent studies have demonstrated that the majority of endogenous cannabinoid type 1 (CB(1)) receptors do not reach the cell surface but are instead associated with endosomal and lysosomal compartments. Using calcium imaging and intracellular microinjection in CB(1) receptor-transfected HEK293 cells and NG108-15 neuroblastoma × glioma cells, we provide evidence that anandamide acting on CB(1) receptors increases intracellular calcium concentration when administered intracellularly but not extracellularly. The calcium-mobilizing effect of intracellular anandamide was dose-dependent and abolished by pretreatment with SR141716A, a CB(1) receptor antagonist. The anandamide-induced calcium increase was reduced by blocking nicotinic acid-adenine dinucleotide phosphate- or inositol 1,4,5-trisphosphate-dependent calcium release and abolished when both lysosomal and endoplasmic reticulum calcium release pathways were blocked. Taken together, our results indicate that, in CB(1) receptor-transfected HEK293 cells, intracellular CB(1) receptors are functional; they are located in acid-filled calcium stores (endolysosomes). Activation of intracellular CB(1) receptors releases calcium from endoplasmic reticulum and lysosomal calcium stores. In addition, our results support a novel role for nicotinic acid-adenine dinucleotide phosphate in cannabinoid-induced calcium signaling.

A Novel Postsynaptic Mechanism for Heterosynaptic Sharing of Short-Term Plasticity

Postsynaptic release of Ca(2+) from intracellular stores is an important means of cellular signaling that mediates numerous forms of synaptic plasticity. Previous studies have identified a postsynaptic intracellular Ca(2+) requirement for a form of short-term plasticity, post-tetanic potentiation (PTP) at sensory neuron (SN)-motor neuron synapses in Aplysia. Here, we show that postsynaptic IP(3)-mediated Ca(2+) release in response to a presynaptic tetanus in an SN that induces PTP can confer transient plasticity onto a neighboring SN synapse receiving subthreshold activation. This heterosynaptic sharing of plasticity represents a dynamic, short-term synaptic enhancement of synaptic inputs onto a common postsynaptic target. Heterosynaptic sharing is blocked by postsynaptic disruption of Ca(2+)- and IP(3)-mediated signaling, and, conversely, it is mimicked by postsynaptic injection of nonhydrolyzable IP(3), and by photolysis of caged IP(3) in the MN. The molecular mechanism for heterosynaptic sharing involves metabotropic glutamate receptors and Homer-dependent interactions, indicating that Homer can facilitate the integration of Ca(2+)-dependent plasticity at neighboring postsynaptic sites and provides a postsynaptic mechanism for the spread of plasticity induced by presynaptic activation. Our results support a model in which postsynaptic summation of IP(3) signals from suprathreshold and subthreshold inputs results in molecular coincidence detection that gives rise to a novel form of heterosynaptic plasticity.

VOLTAGE AND IONIC REGULATION OF HUMAN SEROTONIN TRANSPORTER IN XENOPUS OOCYTES

1. The serotoninergic system is known to be involved in the control of multiple behavioural and physiological functions. The serotonin (5-hydroxtryptamine; 5-HT) transporter (SERT), which controls the synaptic 5-HT concentration through re-uptake of this neurotransmitter into presynaptic terminals, has been a primary therapeutic target for various psychiatric and peripheral disorders. The aim of the present study was to identify the regulatory mechanism(s) of the human SERT (hSERT) in heterologously expressed oocytes. 2. The hSERT cRNA was transcribed in vitro and injected into Xenopus oocytes. The 5-HT-induced transporter currents were measured by voltage clamp. The effects of extracellular sodium or chloride were studied by replacement perfusion with tetramethylammonium-chloride (96 mmol/L) or sodium acetate (96 mmol/L). In addition, to alter the internal calcium concentration, CaCl2 (50 micromol/L) and inositol triphosphate (IP3; 50 micromol/L), with or without EGTA (2.5 mmol/L), were injected into oocytes. The specificity of 5-HT-sensitive currents was determined by the use of the SERT antagonist desipramine and niflumic acid to block background chloride currents. 3. The hSERT-expressing oocytes displayed voltage-dependent, 5-HT-induced currents that increased at negative potentials. Replacing extracellular sodium or chloride significantly decreased the hSERT currents by 89 and 45%, respectively (P < 0.05, n = 7 each). Injection of IP3 or CaCl2 increased the hSERT currents by approximately 65% (P < 0.05; n = 10 each) and the effect of IP3 was abolished by preinjection of EGTA. 4. These results demonstrate that hSERT activity is not only voltage dependent, but is also affected by intracellular calcium and extracellular sodium and chloride.

Modulation of calcium wave propagation in the dendrites and to the soma of rat hippocampal pyramidal neurons.

Repetitive synaptic stimulation in the stratum radiatum (SR) evokes large amplitude Ca2+ waves in the thick apical dendrites of hippocampal CA1 pyramidal neurons. These waves are initiated by activation of metabotropic glutamate receptors (mGluRs), which mobilize inositol-1,4,5-trisphospate (IP3) and release Ca2+ from intracellular stores. We explored mechanisms that modulate the spatial properties of these waves. Higher stimulus current evoked waves of increasing spatial extent. Most waves did not propagate through the soma; the majority stopped close to the junction of the soma and apical dendrite. Pairing strong stimulation with one electrode and subthreshold stimulation with another (associative activation) extended the waves distally but failed to extend waves into the cell body. Pairing synaptic stimulation with backpropagating action potentials enhanced the likelihood of wave generation but did not extend the waves to the somatic region. Priming the stores with Ca2+ entry through voltage dependent channels modulated wave properties but did not extend them past the dendrites. These results are consistent with propagation failing due to the dilution of synaptically generated IP3 as it diffuses into the large volume of the soma (impedance mismatch). Synaptically activating waves in the presence of low concentrations of carbachol, which probably increased the tonic level of IP3 throughout the cell, enhanced the extent of propagation and generated waves that invaded the soma, as long as low-affinity indicators were used to detect the [Ca2+]i changes. Consistent with this explanation direct injection of IP3 into the soma promoted wave propagation into this region. Ca2+ waves that propagated through the cell body were interesting because they did not fill the volume of the soma, but passed through the centre, often with large amplitude. These waves may be particularly effective in activating gene expression and protein synthesis.

379 EFFECT OF SUPPLEMENTARY INOSITOL 1,4,5-TRIPHOSPHATE INJECTION ON FERTILIZATION AND EMBRYO DEVELOPMENT AFTER BOVINE ICSI

During fertilization in mammals, sperm membrane-bound phospholipase C zeta induces breakdown of ooplasmic membrane-bound phosphatidylinositol-4,5-bisphosphate (PIP2), which leads to the production of diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3). The IP3 induces intracellular Ca2+ oscillations ([Ca2+]i), which trigger inactivation of maturation-promoting factor (MPF) and mitogen-activated kinase (MAPK), resulting in decondensation of the sperm head, resumption of meiosis, extrusion of a second polar body, cortical granule exocytosis, formation of pronuclei (PN), and entry into the first cell cycle. In bovine ICSI, injection of a single spermatozoon into an oocyte does not consistently induce [Ca2+]i oscillations, as was observed in IVF, and this may, at least in part, explain the low rates of fertilization and embryo development. Although IP3 has been used as a powerful activator for nuclear transferred zygotes or parthenogenetic oocytes, few studies have evaluated the effect of IP3 injection on normal fertilization and embryo development after ICSI. The objective of this study was to determine the effect of injecting IP3 during bovine ICSI on fertilization and embryo development in vitro. Chemically defined media (CDM) were used throughout (De La Torre-Sanchez et al. 2006 Reprod. Fertil. Dev. 18, 585–596). The injection volume of IP3, which was dissolved in calcium- and magnesium-free PBS, was approximately 0.01 nL, and the total dose for injection along with a spermatozoon was about 250 �M, which was determined by the 2PN formation rate in preliminary experiments. Semen from 3 bulls was used to produce embryos in 5 replicates. Oocytes obtained from slaughterhouse ovaries were matured in vitro in CDM-M for 22–23 h under 5% CO2 in air at 38.5�C, and oocytes with a first polar body were used for ICSI. Motile sperm from frozen–thawed semen were used for sperm injection, with or without IP3 in a 50-�L drop of GMOPS medium, with a piezo-driven pipet of 7–8 �m inner diameter. After ICSI, presumptive zygotes were cultured in CDM-1 for 3 days, and then in CDM-2 for 5 days at 39�C under 5% CO2/5% O2/90% N2. Cleavage and blastocyst development were evaluated at the end of each culture period. Data were subjected to Fisher&amp;apos;s exact test. Cleavage in control and IP3 groups was 36.4 and 50.0%, respectively (P &amp;lt; 0.05). Respective blastocyst rates per oocyte were 5.5 and 13.0% (P &amp;gt; 0.05). This study showed that injection of IP3 during the sperm injection process improved cleavage of bovine oocytes after ICSI.

Role of cumulus cells during maturation of porcine oocytes in the rise in intracellular Ca 2+ induced by inositol 1,4,5-trisphosphate

At the time of fertilization, release of inositol 1,4,5-trisphosphate (IP3) into the cytoplasm of oocytes is said to be induced by hydrolysis of phosphatidylinositol bis phosphate (PI2) via activation of phospholipase C and is responsible for the Ca 2+ oscillation in oocytes immediately after sperm penetration. On the other hand, cumulus cells have been reported to play an important role in cytoplasmic maturation of mammalian oocytes and to affect embryonic development after fertilization. To obtain more information on the role of cumulus cells in cytoplasmic maturation of oocytes, the effects of cumulus cells on the rise in [Ca 2+]i and the rates of activation and development of porcine mature oocytes induced by IP3 injection were investigated. Mature porcine oocytes that had been denuded of their cumulus cells in the early stage of the maturation period had a depressed rise in [Ca 2+]i (4.0–6.0) and reduced rates of activation (31.4–36.8%) and development (10.0–24.4%) induced by IP3 injection compared with those of their cumulus-enclosed counterparts (7.3, 69.1% and 43.8%; P < 0.05). The [Ca 2+]i rise and the rates of activation and development depressed by the removal of cumulus cells were restored by adding pyruvate to the maturation medium. Furthermore, the IP3 injection-induced depression of [Ca 2+]i rise in mature oocytes derived from cumulus-denuded oocytes (DOs) was restored when they were cultured in a medium with pyruvate (3.9–6.3, P < 0.05). Also, mature oocytes from cumulus–oocyte complexes (COCs) cultured in a medium without glucose had a lower rise in [Ca 2+]i than that in mature oocytes from COCs cultured with glucose (7.4–6.0, P < 0.05). Cumulus cells supported porcine oocytes during maturation in the rise in [Ca 2+]i induced by IP3 and the following activation and development of porcine oocytes after injection of IP3. Moreover, we inferred that a function of cumulus cells is to produce pyruvate by metabolizing glucose and to provide oocytes with pyruvate during maturation, thereby promoting oocyte sensitivity to IP3.

276 THE EFFECT OF CUMULUS CELLS DURING MATURATION ON THE RISE IN THE CONCENTRATION OF INTRACELLULAR Ca2+ ([Ca2+]i) OF PORCINE OOCYTES INDUCEDBY INOSITOL 1,4,5-TRISPHOSPHATE

Increase of inositol 1,4,5-triphosphate (IP3) in the cytoplasm of mammalian oocytes is said to be responsible for [Ca2+]i oscillation observed in the oocytes immediately after sperm penetration, and the [Ca2+]i oscillation is known to be essential for the development of embryos. On the other hand, cumulus cells have been reported to play an important role in cytoplasmic maturation of oocytes and affecting the embryonic development. To obtain more information about the role of cumulus cells in cytoplasmic maturation, the effects of cumulus cells during maturation on the rise in [Ca2+]i and on the rate of activation of porcine mature oocytes induced by IP3 injection were investigated. The immature porcine oocytes were divided into three groups: COCs (intact cumulus-oocyte complexes), DOs (oocytes denuded of their cumulus cells), Co-culture (DOs attached to separated cumulus cells). These groups of immature oocytes were cultured in NCSU23 46 h for maturation. To examine the function of cumulus cells, two groups of immature oocytes were also prepared: DOs + pyruvate (DOs put into NCSU23 with pyruvate) and COCs-glucose free (COCs put into NCSU23 without glucose). The mature oocytes from each group were loaded with Ca2+ indicator fluorescent dye Fura2-AM, and then were irradiated by 340 nm and 360 nm of ultraviolet immediately after the injection of IP3. The intensities of emission light caused by the irradiation of 340 nm and 360 nm ultraviolet were recorded as E340 and E360. Since coupling of Ca2+ and the dye intensifies E340, but does not change E360, the level of [Ca2+]i was shown as R (ratio = E340/E360) in this study. Activation rate was calculated by counting the number of the oocytes that formed pronuclei by injection of IP3. ANOVA and Student's t-test were used in this study. Transient rise in [Ca2+]i was observed in the mature oocytes from every group. The peak R of the rise in [Ca2+]i of the mature oocytes derived from COCs, Dos, and Co-culture and induced by IP3 were 7.2, 4.0, and 6.9, respectively. The R of DOs was significantly lower than those of the others (P &lt; 0.05). Also, the activation rate of the mature oocytes from DOs was significantly lower than those from COCs and Co-culture (31, 66, and 66%). The mature oocytes from DOs + pyruvate showed the same level of peak R compared with those from COCs (7.4 and 6.3), but COCs-glucose free showed a slight but significantly lower peak R compared with the mature oocytes from COCs (6.0 and 7.4, P &lt; 0.05). In conclusion, cumulus cells appeared to support the rise in [Ca2+]i of porcine oocytes induced by IP3 during maturation and the following activation. Moreover, a function of cumulus cells supposedly produces pyruvate by metabolizing glucose and provides it to oocytes during maturation for promoting the cytoplasmic maturation. A part of this study was supported by a Grant-in-Aid for the 21st Century COE Program of the Japan MEXT, and by a grant from the Wakayama Prefecture Collaboration of Regional Entities for the Advancement of Technological Excellence of the JST.

Is Ca2+ release from internal stores involved in membrane excitation in characean cells?

An action potential in characean cells is accompanied by an increase in the cytosolic Ca(2+) concentration ([Ca(2+)](c)) which subsequently causes cessation of cytoplasmic streaming. Two Ca(2+ )origins are postulated for the increase in [Ca(2+)](c), extracellular and intracellular ones. For the extracellular origin, a Ca(2+) influx through voltage-dependent Ca(2+)-permeable channels is postulated. For the intracellular origin, a chain of reactions is assumed to occur, involving phosphoinositide-specific phospholipase C (PI-PLC) activation, production of inositol 1,4,5-trisphosphate (IP(3)) and IP(3)-dependent Ca(2+) release from internal stores [Biskup et al. (1999) FEBS Lett. 453: 72]. The hypothesis of the intracellular Ca(2+) origin was tested in three ways: injection of IP(3) into the streaming endoplasm, application of inhibitors of PI-PLC (U73122 and neomycin) and application of an inhibitor of IP(3)-receptor (2-aminoethoxydiphenyl borate; 2APB). Injection of 1 mM IP(3) into Chara cells did not change the rate of cytoplasmic streaming. Both U73122 (20 micro M) and neomycin (200 micro M) did not affect the generation of the action potential, cessation of cytoplasmic streaming and the increase in [Ca(2+)](c) caused by electric stimulus even 20-30 min after application. 2APB depolarized the membrane and inhibited the excitability of the plasma membrane. The results are not consistent with the data obtained by Biskup et al. (1999) who found inhibition of the excitatory inward current by neomycin and U73122. The hypotheses of internal and external Ca(2+) origins are discussed in the light of the present results.

Activated M-phase-promoting factor (MPF) is exported from the nucleus of starfish oocytes to increase the sensitivity of the Ins(1,4,5)P3 receptors.

Starfish oocytes that are extracted from the ovaries are arrested at the prophase of the first meiotic division. At this stage of maturation, they are characterized by a large nucleus called the germinal vesicle. Meiosis resumption (maturation) can be induced in vitro by adding the hormone 1-methyladenine (1-MA) to the seawater in which the oocytes are suspended. Earlier work in our laboratory had detected Ca(2+) increases in both the cytoplasm and the nucleus of the oocytes approx. 2 min after the 1-MA challenge. The nuclear Ca(2+) increase was found to be essential for the continuation of the meiotic cycle, since the injection of bis-(o-aminophenoxy)ethane- N,N,N',N' -tetra-acetic acid (BAPTA) into the nuclear compartment completely blocked the re-initiation of the cell cycle. We have recently confirmed, using confocal microscopy, that the cytoplasmic and nuclear Ca(2+) pools are regulated independently and that the nuclear envelope in starfish oocytes is not freely permeated by the Ca(2+) wave that sweeps across the nuclear region. Studies by others have shown that the sensitivity of the Ins(1,4,5) P (3) (IP(3)) receptors (IP(3)Rs) to IP(3) increases during oocyte maturation, so that they release progressively more calcium in response to the injection of IP(3), as maturation proceeds. We have now shown that the increased sensitivity of the IP(3)Rs may depend on the activation of the cyclin-dependent kinase, MPF (M-phase-promoting factor) that occurs in the nucleus. MPF does not directly phosphorylate IP(3)Rs but phosphorylates instead the actin-binding protein actin depolymerization factor (ADF)/cofilin.

Emergence of a functional coupling between inositol-1,4,5-trisphosphate receptors and calcium channels in developing neocortical neurons

Cortical pyramidal neurons are considered to be less excitable in the immature cortex than in adults. Our previous report revealed that a negative feedback regulation of membrane excitability is highly correlated with a novel form of calcium release from inositol-1,4,5-trisphosphate (IP 3)-sensitive calcium stores (IP 3-assisted calcium-induced calcium release) in neocortical pyramidal neurons under muscarinic cholinergic activation. As a step to understand the ground for the low membrane excitability in immature tissue, we examined development of IP 3-assisted calcium-induced calcium release. In visual cortex neurons from ‘juvenile’ rats (2–3 weeks of age), an enhancement of spike-frequency adaptation occurred at high spike-frequencies (16–22 Hz), whereas the reduction was observed at low frequencies (6–10 Hz). IP 3-assisted calcium-induced calcium release occurred at the higher frequencies only. In ‘early’ postnatal tissue (1 week of age), by contrast, at neither high nor low frequencies did this form of calcium release occur, and muscarinic cholinergic activation always induced a reduction of spike-frequency adaptation at any spike-frequencies. The mechanism for the failure of induction of IP 3-assisted calcium-induced calcium release in ‘early’ postnatal tissue was investigated. Both an ample supply of calcium influx, elicited by higher frequency spike trains, and a supplementary injection of IP 3 through whole-cell pipets, combined together or applied alone, failed to enable IP 3-assisted calcium-induced calcium release in ‘early’ postnatal tissue. Muscarinic cholinergic activation alone induced a conventional IP 3-induced calcium release similar to that observed in neurons from ‘juvenile’ tissue. Together, it is most likely that functional IP 3Rs and calcium channels are already present and functional, but are not yet adequately assembled to allow IP 3-assisted calcium-induced calcium release in cortical pyramidal neurons from rats of 1 week old.

Bovine Nucleus Transplantation by Intracytoplasmic Injection.

This study investigated bovine somatic nucleus transplantation (NT) using an intracytoplasmic injection system in which cumulus cell nuclei were injected into enucleated oocytes by a piezo micromanipulator. Activation of NT embryos was carried out by (1) simultaneous injection of 2-4 pl of inositol 1,4,5 tri-phosphate (IP3) and a donor nucleus into a recipient cytoplasm (IP method), (2) IP method followed by 1.9 mM 6-dimethylaminopurine (DM) treatment for 3.5 h (IP+DM method), or (3) activated after NT by an ionomycin treatment (IA) followed by DM treatment (IA+DM method). We found the frequency of remodeling nuclei and development into blastocyst stage of NT embryos to be: IP, 44% and 9%; IP+DM, 58% and 29%; and IA+DM, 61% and 27%. These results indicate that IP3 injection into the intracytoplasm followed by DM treatment produces a similar bovine oocyte parthenogenetic activation as IA+DM activation treatment, and that intracytoplasmic nucleus injection is an effective method for bovine somatic NT.

Ryanodine-, IP3- and NAADP-dependent calcium stores control acetylcholine release.

Injections of inositol trisphosphate (IP3) or nicotinamide adenine dinucleotide phosphate (NAADP) into the presynaptic neurone of an identified cholinergic synapse in the buccal ganglion of Aplysia californica increased the amplitude of the inhibitory postsynaptic current evoked by a presynaptic action potential. This suggests that Ca2+ release from various Ca2+ stores can modulate acetylcholine (ACh) release. Specific blockade of the calcium-induced calcium release (CICR) mechanism with ryanodine, or of IP3-induced calcium release with heparin, abolished the effects of IP3, but not the effects of NAADP, suggesting the presence of an intracellular Ca2+ pool independent of those containing ryanodine receptors (RyR) or IP3 receptors. To reinforce electrophysiological observations, intracellular [Ca2+]i changes were measured using the fluorescent dye rhod-2. Injections of cyclic ADP-ribose (an activator of RyR), IP3 or NAADP into the presynaptic neurone induced transient increases in the free intracellular Ca2+ concentration. RyR- and IP3-induced increases were prevented by application of respective selective antagonists but not NAADP-induced increases. Our results show that RyR-dependent, IP3-dependent, and NAADP-dependent Ca2+ stores are present in the same presynaptic terminal but are differently involved in the regulation of the presynaptic Ca2+ concentration that triggers transmitter release.