Monitoring trafficking and expression of hemagglutinin-tagged transient receptor potential melastatin 4 channel in mammalian cells

The TRPM4 gene encodes a Ca²⁺-activated monovalent cation channel called transient receptor potential melastatin 4 (TRPM4) that is expressed in various tissues. Dysregulation or abnormal expression of TRPM4 has been linked to a range of diseases. We introduced the hemagglutinin (HA) tag into the extracellular S6 loop of TRPM4, resulting in an HA-tagged version called TRPM4-HA. This TRPM4-HA was developed to investigate the purification, localization, and function of TRPM4 in different physiological and pathological conditions. TRPM4-HA was successfully expressed in the intact cell membrane and exhibited similar electrophysiological properties, such as the current-voltage relationship, rapid desensitization, and current size, compared to the wild-type TRPM4. The presence of the TRPM4 inhibitor 9-phenanthrol did not affect these properties. Furthermore, a wound-healing assay showed that TRPM4-HA induced cell proliferation and migration, similar to the native TRPM4. Co-expression of protein tyrosine phosphatase, non-receptor type 6 (PTPN6 or SHP-1) with TRPM4-HA led to the translocation of TRPM4-HA to the cytosol. To investigate the interaction between PTPN6 and tyrosine residues of TRPM4 in enhancing channel activity, we generated four mutants in which tyrosine (Y) residues were substituted with phenylalanine (F) at the N-terminus of TRPM4. The YF mutants displayed properties and functions similar to TRPM4-HA, except for the Y256F mutant, which showed resistance to 9-phenanthrol, suggesting that Y256 may be involved in the binding site for 9-phenanthrol. Overall, the creation of HA-tagged TRPM4 provides researchers with a valuable tool to study the role of TRPM4 in different conditions and its potential interactions with other proteins, such as PTPN6.

Fermented Soybean Paste Attenuates Biogenic Amine-Induced Liver Damage in Obese Mice

Biogenic amines are cellular components produced by the decarboxylation of amino acids; however, excessive biogenic amine production causes adverse health problems. The relationship between hepatic damage and biogenic amine levels in nonalcoholic fatty liver disease (NAFLD) remains unclear. In this study, mice were fed a high-fat diet (HFD) for 10 weeks to induce obesity, presenting early-stage of NAFLD. We administered histamine (20 mg/kg) + tyramine (100 mg/kg) via oral gavage for 6 days to mice with HFD-induced early-stage NAFLD. The results showed that combined histamine and tyramine administration increased cleaved PARP-1 and IL-1β in the liver, as well as MAO-A, total MAO, CRP, and AST/ALT levels. In contrast, the survival rate decreased in HFD-induced NAFLD mice. Treatment with manufactured or traditional fermented soybean paste decreased biogenically elevated hepatic cleaved PARP-1 and IL-1β expression and blood plasma MAO-A, CRP, and AST/ALT levels in HFD-induced NAFLD mice. Additionally, the biogenic amine-induced reduction in survival rate was alleviated by fermented soybean paste in HFD-induced NAFLD mice. These results show that biogenic amine-induced liver damage can be exacerbated by obesity and may adversely affect life conservation. However, fermented soybean paste can reduce biogenic amine-induced liver damage in NAFLD mice. These results suggest a beneficial effect of fermented soybean paste on biogenic amine-induced liver damage and provide a new research perspective on the relationship between biogenic amines and obesity.

Dipeptide YA is Responsible for the Positive Effect of Oyster Hydrolysates on Alcohol Metabolism in Single Ethanol Binge Rodent Models

Accumulative alcohol hangovers cause liver damage through oxidative and inflammatory stress. Numerous antioxidant and anti-inflammatory reagents have been developed to reduce alcohol hangovers, but these reagents are still insignificant and have limitations in that they can cause liver toxicity. Oyster hydrolysate (OH), another reagent that has antioxidant and anti-inflammatory activity, is a product extracted through an enzymatic hydrolysis process from oysters (Crassostrea gigas), which can be easily eaten in meals. This study was aimed at determining the effects of OH on alcohol metabolism, using a single high dose of ethanol (EtOH) administered to rodents, by monitoring alcohol metabolic enzymes, oxidative stress signals, and inflammatory mediators. The effect of tyrosine-alanine (YA) peptide, a main component of OH, on EtOH metabolism was also identified. In vitro experiments showed that OH pretreatment inhibited EtOH-induced cell death, oxidative stress, and inflammation in liver cells and macrophages. In vivo experiments showed that OH and YA pre-administration increased alcohol dehydrogenase, aldehyde dehydrogenase, and catalase activity in EtOH binge treatment. In addition, OH pre-administration alleviated CYP2E1 activity, ROS production, apoptotic signals, and inflammatory mediators in liver tissues. These results showed that OH and YA enhanced EtOH metabolism and had a protective effect against acute alcohol liver damage. Our findings offer new insights into a single high dose of EtOH drinking and suggest that OH and YA could be used as potential marine functional foods to prevent acute alcohol-induced liver damage.

Endophytic and endolichenic fungal diversity in maritime Antarctica based on cultured material and their evolutionary position among Dikarya

Fungal endophytes comprise one of the most ubiquitous groups of plant symbionts. They live asymptomatically within vascular plants, bryophytes and also in close association with algal photobionts inside lichen thalli. While endophytic diversity in land plants has been well studied, their diversity in lichens and bryophytes are poorly understood. Here, we compare the endolichenic and endophytic fungal communities isolated from lichens and bryophytes in the Barton Peninsula, King George Island, Antarctica. A total of 93 fungal isolates were collected from lichens and bryophytes. In order to determine their identities and evolutionary relationships, DNA sequences of the nuclear internal transcribed spacer (ITS), nuclear ribosomal small subunit (nuSSU), nuclear large subunit (nuLSU), and mitochondrial SSU (mtSSU) rDNA were obtained and protein coding markers of the two largest subunit of RNA polymerase II (RPB1 and RPB2) were generated. Multilocus phylogenetic analyses revealed that most of the fungal isolates were distributed in the following six classes in the phylum Ascomycota: Dothideomycetes, Eurotiomycetes, Lecanoromycetes, Leotiomycetes, Pezizomycetes and Sordariomycetes. For the first time we report the presence of subphylum Mortierellomycotina that may belong to an undescribed order in endophytic fungi. Taken together, our results imply that lichens and bryophytes provide similar niches and harbour a selection of these fungi, indicating generalists within the framework of evolutionary adaptation.

Activation of TREK-1, but Not TREK-2, Channel by Mood Stabilizers

Earlier studies have demonstrated that the tandem pore domain weak inward rectifying K⁺ channel (TWIK)-related K⁺ (TREK)-1 channel is inhibited by antidepressants and is associated with major depression. However, little is known about the effect of mood stabilizers that are commonly used for treatment of bipolar disorder on TREK channels, members of the two-pore domain K⁺ (K_2P) channel family. This study sought to investigate the effect of mood stabilizers on TREK-1 and TREK-2 channels. HEK-293A cells were transfected with human TREK-1 or TREK-2 DNA. The effect of mood stabilizers on TREK-1 and TREK-2 was studied using the patch clamp technique. Changes in TREK protein expression by mood stabilizers were studied in the HT-22 mouse hippocampal neuronal cells using western blot analysis. Lithium chloride (LiCl, 1 mM), gabapentin (100 μM), valproate (100 μM), and carbamazepine (100 μM) increased TREK-1 currents by 31 ± 14%, 25 ± 11%, 28 ± 12%, and 72 ± 12%, respectively, whereas they had no effect on TREK-2 channel activity. In addition, western blot analysis showed LiCl and carbamazepine slightly upregulated TREK-1 expression, but not TREK-2 in the HT-22 cells. These results suggest that TREK-1 could be a potential therapeutic target for treatment of bipolar disorders as well as depression, while TREK-2 is a target well suited for treatment of major depression.

Copine1 C2 domains have a critical calcium-independent role in the neuronal differentiation of hippocampal progenitor HiB5 cells

Copine1 (CPNE1) has tandem C2 domains and an A domain and is known as a calcium-dependent membrane-binding protein that regulates signal transduction and membrane trafficking. We previously demonstrated that CPNE1 directly induces neuronal differentiation via Akt phosphorylation in the hippocampal progenitor cell line, HiB5. To determine which region of CPNE1 is related to HiB5 cell neurite outgrowth, we constructed several mutants. Our results show that over-expression of each C2 domain of CPNE1 increased neurite outgrowth and expression of the neuronal marker protein neurofilament (NF). Even though protein localization of the calcium binding-deficient mutant of CPNE1 was not affected by ionomycin, this mutant increased neurite outgrowth and NF expression in HiB5 cells. Furthermore, Akt phosphorylation was increased by over-expression of the calcium binding-deficient CPNE1 mutant. These results suggest that neither cellular calcium levels nor the localization of CPNE1 affect its function in neuronal differentiation. Collectively, our findings indicating that the C2 domains of CPNE1 play a calcium-independent role in regulating the neuronal differentiation of HiB5 cells.

A Novel Cytosolic Isoform of Mitochondrial Trans-2-Enoyl-CoA Reductase Enhances Peroxisome Proliferator-Activated Receptor α Activity

BACKGROUND

Mitochondrial trans-2-enoyl-CoA reductase (MECR) is involved in mitochondrial synthesis of fatty acids and is highly expressed in mitochondria. MECR is also known as nuclear receptor binding factor-1, which was originally reported with yeast two-hybrid screening as a binding protein of the nuclear hormone receptor peroxisome proliferator-activated receptor α (PPARα). However, MECR and PPARα are localized at different compartment, mitochondria, and the nucleus, respectively. Therefore, the presence of a cytosolic or nuclear isoform of MECR is necessary for functional interaction between MECR and PPARα.

METHODS

To identify the expression pattern of MECR and the cytosolic form of MECR (cMECR), we performed reverse transcription polymerase chain reaction (RT-PCR) with various tissue samples from Sprague-Dawley rats. To confirm the interaction between cMECR and PPARα, we performed several binding assays such as yeast two-hybrid, coimmunoprecipitation, and bimolecular fluorescence complementation. To observe subcellular localization of these proteins, immunocytochemistry was performed. A luciferase assay was used to measure PPARα activity.

RESULTS

We provide evidence of an alternatively spliced variant of the rat MECR gene that yields cMECR. The cMECR lacks the N-terminal 76 amino acids of MECR and shows uniform distribution in the cytoplasm and nucleus of HeLa cells. cMECR directly bound PPARα in the nucleus and increased PPARα-dependent luciferase activity in HeLa cells.

CONCLUSION

We found the cytosolic form of MECR (cMECR) was expressed in the cytosolic and/or nuclear region, directly binds with PPARα, and enhances PPARα activity.

The molecular mechanism of NELL2 movement and secretion in hippocampal progenitor HiB5 cells

Neural epidermal growth factor-like protein-like 2 (NELL2) is a secreted glycoprotein that is predominantly expressed in the nervous system, but little is known about the intracellular movement and secretion mechanism of this protein. By monitoring the localization and movements of enhanced green fluorescent protein (EGFP)-labeled NELL2 in living cultured hippocampal neuroprogenitor HiB5 cells, we determined the subcellular localization of NELL2 and its intracellular movement and secretion mechanism. Cterminal EGFP-fused NELL2 showed a typical expression pattern of secreted proteins, especially with respect to its localization in the endoplasmic reticulum, Golgi apparatus, and punctate structures. Vesicles containing NELL2 exhibited bidirectional movement in HiB5 cells. The majority of the vesicles (70.1%) moved in an anterograde direction with an average velocity of 0.454 μm/s, whereas some vesicles (28.7%) showed retrograde movement with an average velocity of 0.302 μm/s. The movement patterns of NELL2 vesicles were dependent upon the presence of microtubules in HiB5 cells. Anterograde movement of NELL2 did not lead to a detectable accumulation of NELL2 in the peripheral region of the cell, indicating that it was secreted into the culture medium. We also showed that the N-terminal 29 amino acids of NELL2 were important for secretion of this protein. Taken together, these results strongly suggest that the N-terminal region of NELL2 determines both the pattern of its intracellular expression and transport of NELL2 vesicles by high-velocity movement. Therefore, NELL2 may affect the cellular activity of cells in a paracrine or autocrine manner.

SYT14L, especially its C2 domain, is involved in regulating melanocyte differentiation

BACKGROUND

The formation of dendrites by melanocytes is highly analogous to that process in neural cells. We previously reported that a C2 domain-containing protein, copine-1, is involved in the extension of dendrites by neural cells. However, the effect of C2 domain-containing proteins in dendrite formation by melanocytes has not yet been elucidated.

OBJECTIVE

The aim of this study was to screen novel C2 domain-containing proteins related to dendrite outgrowth in melanocytes and to investigate their precise roles in melanocyte dendrite formation during differentiation.

METHODS

We transduced mouse melan-a melanocytes with a recombinant adenovirus expressing a C2 domain library. Dendrite elongation, melanin content, tyrosinase activity and Western blot analyses were conducted to elucidate the possible underlying mechanisms of action in melanocytes.

RESULTS

Sixteen sets of C2 domain-containing proteins were identified whose over-expression resulted in dendrite lengthening. Among those, we focused on the C2 domain of SYT14L (truncated mutant of SYT14L) in this study. Forced expression of full length SYT14L or the C2 domain of SYT14L induced a significant elongation of dendrite length accompanied by the induction of melanocyte differentiation-related markers, including melanin synthesis, tyrosinase catalytic activity and the expression of tyrosinase (TYR), tyrosinase related protein-1 (TRP-1) and TRP-2. In addition, over-expression of either the C2 domain or the full length form of SYT14L significantly increased the phosphorylation of ERK and CREB.

CONCLUSION

These results suggest that SYT14L, especially its C2 domain, may play an important role in regulating melanocyte differentiation through the modulation of ERK and (or) CREB signaling.

Acute Hypoxia Activates an ENaC-like Channel in Rat Pheochromocytoma (PC12) Cells

Cells can resist and even recover from stress induced by acute hypoxia, whereas chronic hypoxia often leads to irreversible damage and eventually death. Although little is known about the response(s) to acute hypoxia in neuronal cells, alterations in ion channel activity could be preferential. This study aimed to elucidate which channel type is involved in the response to acute hypoxia in rat pheochromocytomal (PC12) cells as a neuronal cell model. Using perfusing solution saturated with 95% N(2) and 5% CO(2), induction of cell hypoxia was confirmed based on increased intracellular Ca(2+) with diminished oxygen content in the perfusate. During acute hypoxia, one channel type with a conductance of about 30 pS (2.5 pA at -80 mV) was activated within the first 2~3 min following onset of hypoxia and was long-lived for more than 300 ms with high open probability (P(o), up to 0.8). This channel was permeable to Na(+) ions, but not to K(+), Ca(+), and Cl(-) ions, and was sensitively blocked by amiloride (200 nM). These characteristics and behaviors were quite similar to those of epithelial sodium channel (ENaC). RT-PCR and Western blot analyses confirmed that ENaC channel was endogenously expressed in PC12 cells. Taken together, a 30-pS ENaC-like channel was activated in response to acute hypoxia in PC12 cells. This is the first evidence of an acute hypoxia-activated Na(+) channel that can contribute to depolarization of the cell.

Copine1 enhances neuronal differentiation of the hippocampal progenitor HiB5 cells

Copine1 is a ubiquitously expressed protein found in various tissues including the brain, but little is known about the physiological function of this protein. Here, we showed that copine1 is involved in neuronal differentiation. Over-expression of copine1 clearly increased neurite outgrowth and expression of Tuj1, a neuronal marker protein, in HiB5 cells. In addition, endogenous copine1 was transiently increased at the early time during neuronal differentiation of HiB5 cells. When the expression of endogenous copine1 was knocked-down by its specific shRNA, PDGF-mediated neurite outgrowth was clearly decreased in HiB5 cells. Furthermore, over-expression of copine1 increased phosphorylation of Akt and copine1-specific shRNA decreased phosphorylation of Akt during neuronal differentiation of HiB5 cells. Interestingly, the phosphorylation level of PI3K, generally known as an upstream protein of Akt, was not changed by copine1 expression. These results suggest that copine1 enhances neuronal differentiation of HiB5 cells not through the PI3K-Akt pathway, but by using another Akt activated signal pathway.

Effect of dimethyl sulfoxide on cell cycle synchronization of goldfish caudal fin derived fibroblasts cells

Several studies have previously been conducted regarding cell cycle synchronization in mammalian somatic cells. However, limited work has been performed on the control of cell cycle stages in the somatic cells of fish. The aim of this study was to determine the cell cycle arresting effects of several dimethyl sulfoxide (DMSO) concentrations for different times on different cell cycle stages of goldfish caudal fin-derived fibroblasts. Results demonstrated that the cycling cells or control group (68.29%) yields significantly higher (p < 0.05) arrest in G0/G1 phase compared with the group treated for 24 h with different concentrations (0.5%, 1.0% or 1.5%) of DMSO (64.88%, 65.70%, 64.22% respectively). The cell cycle synchronization in the treatment of cells with 1.0% DMSO at 48 h (81.14%) was significantly higher than that in the groups treated for 24 h (76.82%) and the control group (77.90%). Observations showed that treatment of DMSO resulted in an increase in the proportion of cells at G0/G1 phase for 48 h of culture. However, high levels of apoptotic cells can be detected after 48 h of culture treated with 1% concentration of DMSO.

Influence of oocyte donor and embryo recipient conditions on cloning efficiency in dogs

To determine factors that affect the efficiency of dog cloning by somatic cell nuclear transfer, the present study was performed to investigate 1) the effects of surgical history (non-operated/operated) and parity (nullipara/multipara) on the recovery of in vivo canine oocytes; 2) the effects of surgical history and parity of recipients on the pregnancy and delivery; and 3) the effects of synchronization state (AA, advanced asynchrony; SY, synchrony; RA, retarded asynchrony) between oocytes donor and recipient on the pregnancy and delivery. Oocyte recovery rate was significantly higher in non-operated dogs compared to operated dogs (93.8 vs. 89.6%, P < 0.05) and not different between nulliparous dogs and multiparous dogs. Delivery rate was also significantly higher in non-operated dogs compared to operated dogs (2.8 vs. 1.0%, P < 0.05) and in nulliparous dogs than multiparous dogs (3.0 vs. 1.7%, P < 0.05). Even though SY showed increased pregnancy and delivery rate (20.0% and 3.0%) compared to AA (15.0% and 2.0%) and RA (0.0% and 0.0%), there was no significant difference. In conclusion, we recommend non-operated dogs as experimental dogs and nulliparous dogs as recipient dogs to increase delivery rate after transfer of somatic cell nuclear transferred embryos, but further study is needed to find out appropriate synchrony status at the transfer.

Enhancement of TREK1 channel surface expression by protein-protein interaction with beta-COP

TREK1 belongs to a family of two-pore-domain K(+) (K(2P)) channels and produce background currents that regulate cell excitability. In the present study, we identified a vesicle transport protein, beta-COP, as an interacting partner by yeast two-hybrid screening of a human brain cDNA library with N-terminal region of TREK1 (TREK1-N) as bait. Several in vitro and in vivo binding assays confirmed the protein-protein interaction between TREK1 and beta-COP. We also found that beta-COP was associated with TREK1 in native condition at the PC3 cells. When RFP-beta-COP was co-transfected with GFP-TREK1 into COS-7 cells, both proteins were found localized to the plasma membrane. In addition, the channel activity and surface expression of GFP-TREK1 increased dramatically by co-transfection with RFP-beta-COP. Surface expression of the TREK1 channel was also clearly reduced with the addition of beta-COP-specific shRNA. Collectively, these data suggest that beta-COP plays a critical role in the forward transport of TREK1 channel to the plasma membrane.

Diclofenac, a Non-steroidal Anti-inflammatory Drug, Inhibits L-type Ca Channels in Neonatal Rat Ventricular Cardiomyocytes

A non-steroidal anti-inflammatory drug (NSAID) has many adverse effects including cardiovascular (CV) risk. Diclofenac among the nonselective NSAIDs has the highest CV risk such as congestive heart failure, which resulted commonly from the impaired cardiac pumping due to a disrupted excitation-contraction (E-C) coupling. We investigated the effects of diclofenac on the L-type calcium channels which are essential to the E-C coupling at the level of single ventricular myocytes isolated from neonatal rat heart, using the whole-cell voltage-clamp technique. Only diclofenac of three NSAIDs, including naproxen and ibuprofen, significantly reduced inward whole cell currents. At concentrations higher than 3 microM, diclofenac inhibited reversibly the Na(+) current and did irreversibly the L-type Ca(2+) channels-mediated inward current (IC(50)=12.89+/-0.43 microM) in a dose-dependent manner. However, nifedipine, a well-known L-type channel blocker, effectively inhibited the L-type Ca(2+) currents but not the Na(+) current. Our finding may explain that diclofenac causes the CV risk by the inhibition of L-type Ca(2+) channel, leading to the impairment of E-C coupling in cardiac myocytes.

Caveolin-2 regulation of STAT3 transcriptional activation in response to insulin

The regulatory function of caveolin-2 in signal transducer and activator of transcription 3 (STAT3) signaling by insulin was investigated. Insulin-induced increase in phosphorylation of STAT3 was reduced by caveolin-2 siRNA. Mutagenesis studies identified that phosphorylation of tyrosines 19 and 27 on caveolin-2 is required for the STAT3 activation. Caveolin-2 Y27A mutation decreased insulin-induced phosphorylation of STAT3 interacting with caveolin-2. pY27-Caveolin-2 was required for nuclear translocation of pY705-STAT3 in response to insulin. In contrast, caveolin-2 Y19A mutation influenced neither the phosphorylation of STAT3 nor nuclear translocation of pY705-STAT3. pY19-Caveolin-2, however, was essential for insulin-induced DNA binding of pS727-STAT3 and STAT3-targeted gene induction in the nucleus. Finally, insulin-induced transcriptional activation of STAT3 depended on phosphorylation of both 19 and 27 tyrosines. Together, our data reveal that phosphotyrosine-caveolin-2 is a novel regulator for transcriptional activation of STAT3 in response to insulin.

Silencing of Kv4.1 potassium channels inhibits cell proliferation of tumorigenic human mammary epithelial cells

Potassium channel activity has been shown to facilitate cell proliferation in cancer cells. In the present study, the role of Kv4.1 channels in immortal and tumorigenic human mammary epithelial cells was investigated. Kv4.1 protein expression was positively correlated with tumorigenicity. Moreover, transfection with siRNAs targeting Kv4.1 mRNA suppressed proliferation of tumorigenic mammary epithelial cells. Experiments using mRNA isolated from human breast cancer tissues revealed that the level of Kv4.1 mRNA expression varied depending on the stage of the tumor. Kv4.1 protein expression increased during stages T2 and T3 compared to normal tissue. These results demonstrated that Kv4.1 plays a role in proliferation of tumorigenic human mammary epithelial cells. In addition, elevated Kv4.1 expression may be useful as a diagnostic marker for staging mammary tumors and selective blockers of Kv4.1 may serve to suppress tumor cell proliferation.

Effects of activin A on the in vitro development and mRNA expression of bovine embryos cultured in chemically-defined two-step culture medium

The purpose of the present study was to evaluate the effects of activin A on the developmental competence of in vitro fertilized (IVF) bovine embryos derived from a two-step defined culture system (C1/C2 medium) during the early or later stages of embryo development. To evaluate the effects of activin A on transcriptional levels, we analysed genes related to blastocyst hatching and implantation and to activin signalling pathway in IVF embryos. Cumulus-oocyte complexes were matured for 22 h and fertilized in vitro. Presumptive zygotes were cultured in the presence or absence of activin A during early (0-120 h, C1) or later (120-192 h, C2) stages. Although the developmental competence of embryos cultured with activin A in C1 medium was not significantly different from their corresponding controls, development to blastocysts (22.4% vs 34.7%; p < 0.05) and the blastocyst hatching rate (9.3% vs 22.4%; p < 0.05) in C2 medium supplemented with 100 ng/ml activin A were significantly higher than in the control group. To evaluate the effect of activin A on transcription, the relative expression levels of genes related to blastocyst hatching and implantation (Na/K-ATPase, E-cad and Glut-1) as well as activin signalling pathway (ActRII, ActRIIB and Smad2) were analysed. Compared to control medium, gene expression of Na/K-ATPase, E-cad, Glut-1, ActRII and ActRIIB was increased in medium supplemented with activin A. In conclusion, this study suggests that activin A, during the later stage of in vitro bovine embryo development, can enhance in vitro development of embryos by increasing hatching rates and affecting expression levels of genes related to hatching and implantation in defined culture medium.

Expression and localization of two-pore domain K(+) channels in bovine germ cells

Two-pore domain K(+) (K(2P)) channels that help set the resting membrane potential of excitable and nonexcitable cells are expressed in many kinds of cells and tissues. However, the expression of K(2P) channels has not yet been reported in bovine germ cells. In this study, we demonstrate for the first time that K(2P) channels are expressed in the reproductive organs and germ cells of Korean cattle. RT-PCR data showed that members of the K(2P) channel family, specifically KCNK3, KCNK9, KCNK2, KCNK10, and KCNK4, were expressed in the ovary, testis, oocytes, embryo, and sperm. Out of these channels, KCNK2 and KCNK4 mRNAs were abundantly expressed in the mature oocytes, eight-cell stage embryos, and blastocysts compared with immature oocytes. KCNK4 and KCNK3 were significantly increased in eight-cell stage embryos. Immunocytochemical data showed that KCNK2, KCNK10, KCNK4, KCNK3, and KCNK9 channel proteins were expressed at the membrane of oocytes and blastocysts. KCNK10 and KCNK4 were strongly expressed and distributed in oocyte membranes. These channel proteins were also localized to the acrosome sperm cap. In particular, KCNK3 and KCNK4 were strongly localized to the post-acrosomal region of the sperm head and the equatorial band within the sperm head respectively. These results suggest that K(2P) channels might contribute to the background K(+) conductance of germ cells and regulate various physiological processes, such as maturation, fertilization, and development.

Single-Channel Recording of TASK-3-like K Channel and Up-Regulation of TASK-3 mRNA Expression after Spinal Cord Injury in Rat Dorsal Root Ganglion Neurons

Single-channel recordings of TASK-1 and TASK-3, members of two-pore domain K(+) channel family, have not yet been reported in dorsal root ganglion (DRG) neurons, even though their mRNA and activity in whole-cell currents have been detected in these neurons. Here, we report single-channel kinetics of the TASK-3-like K(+) channel in DRG neurons and up-regulation of TASK-3 mRNA expression in tissues isolated from animals with spinal cord injury (SCI). In DRG neurons, the single-channel conductance of TASK-3-like K(+) channel was 33.0+/-0.1 pS at -60 mV, and TASK-3 activity fell by 65+/-5% when the extracellular pH was changed from 7.3 to 6.3, indicating that the DRG K(+) channel is similar to cloned TASK-3 channel. TASK-3 mRNA and protein levels in brain, spinal cord, and DRG were significantly higher in injured animals than in sham-operated ones. These results indicate that TASK-3 channels are expressed and functional in DRG neurons and the expression level is up-regulated following SCI, and suggest that TASK-3 channel could act as a potential background K(+) channel under SCI-induced acidic condition.

Expression of thermosensitive two-pore domain K+ channels in human keratinocytes cell line HaCaT cells

Recent studies have shown that keratinocytes can sense temperature via thermo-transient receptor potential (TRP) channels. It is not known whether other thermosensitive ion channels such as TREK-1, TREK-2 and TRAAK (TREKs/TRAAK) that are members of the two-pore domain K(+) (K(2P)) channel family are expressed in human keratinocytes. Here, we identified the expression of TREKs/TRAAK in human keratinocytes-derived cell line HaCaT cells using RT-PCR, immunocytochemistry, Western blot analysis and patch-clamp technique. RT-PCR showed that all six K(2P) channels tested (TASK-1, TASK-3, TREK-1, TREK-2, TRAAK and TASK-2) were expressed in HaCaT cells, as well as in skin and dorsal root ganglion (DRG) of rat. The expression of TREKs/TRAAK mRNA identified by RT-PCR was further studied at the protein level. Using anti-TREK-1, -TREK-2 and -TRAAK, bands of approximately 46, approximately 60 and approximately 43 kDa, respectively, were observed at plasma membrane of HaCaT cells. Immunostaining also showed that TREK-1, TREK-2 and TRAAK were expressed in all area of cells including plasma membrane. Whole-cell K(+) currents recorded from HaCaT cells were activated by arachidonic acid and heat. These results suggest that TREKs/TRAAK channels could act as thermosensors in human keratinocytes.

Endogenous TRPM4-like channel in Chinese hamster ovary (CHO) cells

Chinese hamster ovary (CHO) cells used in many transfection studies have been found to endogenously express channels permeable to monovalent cations, but not to divalent cations. In the presence of intracellular Ca(2+), 23-pS channel with a linear current-voltage (I-V) relationship could be frequently observed in inside-out patches but not in cell-attached patches. The open probability was voltage-dependent, which is higher at positive potentials. The channel was dose-dependently activated by relatively high level of Ca(2+) (EC(50)=1.04+/-0.08 mM), and sensitively inhibited by 100 microM ATP, ADP, AMP, and 1mM spermine. However, ruthenium red (2 microM) had no effect. Reverse transcript polymerase chain reaction (RT-PCR) supported the presence of mRNA encoding TRPM4b channel protein. Western blot assay finally confirmed the presence of this channel protein in membrane fraction of CHO cells. These results provide evidence that CHO cells express an endogenous TRPM4b-like channel, and thereby can be used as a tool to study de novo regulation/modulation of TRPM4 channel.

TRPM4b channel suppresses store-operated Ca2+ entry by a novel protein-protein interaction with the TRPC3 channel

We identified human TRPC3 protein by yeast two-hybrid screening of a human brain cDNA library with human TRPM4b as a bait. Immunoprecipitation and confocal microscopic analyses confirmed the protein-protein interaction between TRPM4b and TRPC3, and these two TRPs were found to be highly colocalized at the plasma membrane of HEK293T cells. Overexpression of TRPM4b suppressed TRPC3-mediated whole cell currents by more than 90% compared to those in TRPC3-expressed HEK293T cells. Furthermore, HEK293T cells stably overexpressing red fluorescent protein (RFP)-TRPM4b exhibited an almost complete abolition of UTP-induced store-operated Ca(2+) entry, which is known to take place via endogenous TRPC channels in HEK293T cells. This study is believed to provide the first clear evidence that TRPM4b interacts physically with TRPC3, a member of a different TRP subfamily, and regulates negatively the channel activity, in turn suppressing store-operated Ca(2+) entry through the TRPC3 channel.

Lamotrigine inhibits TRESK regulated by G-protein coupled receptor agonists

Dorsal root ganglion (DRG) neurons express mRNAs for numerous two-pore domain K(+) (K(2P)) channels and G-protein coupled receptors (GPCR). Recent studies have shown that TRESK is a major background K(+) channel in DRG neurons. Here, we demonstrate the pharmacological properties of TRESK, including GPCR agonist-induced effects on DRG neurons. TRESK mRNA was highly expressed in DRG compared to brain and spinal cord. Similar to cloned TRESK, native TRESK was inhibited by acid and arachidonic acid (AA), but not zinc. Native TRESK was also activated by GPCR agonists such as acetylcholine, glutamate, and histamine. The glutamate-activated TRESK was blocked by lamotrigine in DRG neurons. In COS-7 cells transfected with mouse TRESK, 30 microM lamotrigine inhibited TRESK by approximately 50%. Since TRESK is target of modulation by acid, AA, GPCR agonists, and lamotrigine, it is likely to play an active role in the regulation of excitability in DRG neurons.

Sulfonate chalcone as new class voltage-dependent K+ channel blocker

Chalcone derivatives 1-17 were synthesized and their voltage-dependent K+ channel inhibitory activities were investigated. The effective K+ channel blockers were shown to be sulfonate chalcones 9-17, in which the sulfonyloxy group is placed on the A-ring. The 3'-(p-aminobenzene-sulfonylhydroxy)-4-hydroxychalcone 17 (IC50 = 0.51+/-0.05 microM) was the most potent K+ channel blocker.

Improvement of canine somatic cell nuclear transfer procedure

The purpose of the present study on canine somatic cell nuclear transfer (SCNT) was to evaluate the effects of fusion strength, type of activation, culture media and site of transfer on developmental potential of SCNT embryos. We also examined the potential of enucleated bovine oocytes to serve as cytoplast recipients of canine somatic cells. Firstly, we evaluated the morphological characteristics of in vivo-matured canine oocytes collected by retrograde flushing of the oviducts 72 h after ovulation. Secondly, the effectiveness of three electrical strengths (1.8, 2.3 and 3.3 kV/cm), used twice for 20 micros, on fusion of canine cytoplasts with somatic cells were compared. Then, we compared: (1) chemical versus electrical activation (a) after parthenogenetic activation or (b) after reconstruction of canine oocytes with somatic cells; (2) culture of resulting intergeneric (IG) embryos in either (a) mSOF or (b) TCM-199. The exposure time to 6-DMAP was standardized by using bovine oocytes reconstructed with canine somatic cells. Bovine oocytes were used for SCNT after a 22 h in vitro maturation interval. The fusion rate was significantly higher in the 3.3 kV/cm group than in the 1.8 and 2.3 kV/cm treatment groups. After parthenogenesis or SCNT with chemical activation, 3.4 and 5.8%, respectively, of the embryos developed to the morula stage, as compared to none of the embryos produced using electrical activation. Later developmental stages (8-16 cells) were transferred to the uterine horn of eight recipients, but no pregnancy was detected. However, IG cloned embryos (bovine cytoplast/canine somatic cell) were capable of in vitro blastocyst development. In vitro developmental competence of IG cloned embryos was improved after exposure to 6-DMAP for 4 h as compared to 0, 2 or 6h exposure, although the increase was not significantly different among culture media. In summary, for production of canine SCNT embryos, we recommend fusion at 3.3 kV/cm, chemical activation, culture in mSOF medium and transfer of presumptive zygotes to the oviduct of recipient animals. The feasibility of IG production of cloned canine embryos using bovine cytoplasts as recipient of canine somatic cells was demonstrated.

Acetylcholine increases Ca2+ influx by activation of CaMKII in mouse oocytes

IP3-induced Ca2+ release is the primary mechanism that is responsible for acetylcholine (ACh)-induced Ca2+ oscillation. However, other mechanisms remain to explain intracellular Ca2+ elevation. We here report that ACh induces Ca2+ influx via T-type Ca2+ channel by activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII), and the ACh-induced Ca2+ influx facilitates the generation of Ca2+ oscillation in the mouse ovulated oocytes (oocytes(MII)). ACh increased Ca2+ current by 50+/-21%, and produced Ca2+ oscillation. However, the currents and Ca2+ peaks were reduced in Ca2+ -free extracellular medium. ACh failed to activate Ca2+ current and to produce Ca2+ oscillation in oocytes pretreated with KN-93, a CaMKII inhibitor. KN-92, an inactive analogue of KN93, and PKC modulators could not prevent the effect of ACh. These results show that ACh increases T-type Ca2+ current by activation of CaMKII, independent of the PKC pathway, in the mouse oocytes.

Gateway RFP-fusion vectors for high throughput functional analysis of genes

There is an increasing demand for high throughput (HTP) methods for gene analysis on a genome-wide scale. However, the current repertoire of HTP detection methodologies allows only a limited range of cellular phenotypes to be studied. We have constructed two HTP-optimized expression vectors generated from the red fluorescent reporter protein (RFP) gene. These vectors produce RFP-tagged target proteins in a multiple expression system using gateway cloning technology (GCT). The RFP tag was fused with the cloned genes, thereby allowing us localize the expressed proteins in mammalian cells. The effectiveness of the vectors was evaluated using an HTP-screening system. Sixty representative human C2 domains were tagged with RFP and overexpressed in HiB5 neuronal progenitor cells, and we studied in detail two C2 domains that promoted the neuronal differentiation of HiB5 cells. Our results show that the two vectors developed in this study are useful for functional gene analysis using an HTP-screening system on a genome-wide scale.

Alternative splicing generates a novel non-secretable cytosolic isoform of NELL2

NELL2 is as a neuron-specific secreted glycoprotein. The present study provides evidence of an alternatively spliced variant of the rat NELL2 gene that yields cytosolic NELL2 (cNELL2). cNELL2 was initially detected in the thymus and subsequently found to be ubiquitously expressed in many other tissues. The absence of the sequences corresponding to the third exon, which contains the terminal portion of the signal peptide, accounts for the uniform distribution of cNELL2 throughout the cytoplasm. This is in contrast to NELL2, which is preferentially located at distinct subcellular structures involved in the secretary process, such as endoplasmic reticulum and Golgi apparatus. Western blot analysis showed that cNELL2 was not present in the medium but only in lysates, while NELL2 was detected as a glycosylated larger form in both lysates and media. Immunoprecipitation analysis revealed that cNELL2 interacts with PKCbeta1. These results suggest that cNELL2 is involved in PKCbeta1-mediated intracellular signaling.

Birth of viable female dogs produced by somatic cell nuclear transfer

Since the only viable cloned offspring born in dogs was a male, the purpose of the present study was to produce female puppies by somatic cell nuclear transfer (SCNT). Adult ear fibroblasts from a 2-month-old female Afghan hound were isolated and used as donor cells. In vivo-matured canine oocytes surgically collected (approximately 72h after ovulation) from the oviducts of 23 donors were used for SCNT. After removal of the cumulus cells, oocytes were enucleated, microinjected, fused with a donor cell, and activated. A total of 167 reconstructed SCNT embryos were surgically transferred (Day 0) into the oviducts of 12 recipient bitches (average 13.9 embryos/recipient, range 6-22) with spontaneous, synchronous estrous cycles. Three pregnancies were detected by ultrasonography on Day 23, maintained to term, and three healthy female puppies (520, 460, and 520g), were delivered by Caesarean section on Day 60. These puppies were phenotypically and genotypically identical to the cell donor. In conclusion, we have provided the first demonstration that female dogs can be produced by nuclear transfer of ear fibroblasts into enucleated canine oocytes.

A novel acid-sensitive K+ channel in rat dorsal root ganglia neurons

Recent studies have suggested that acid-sensitive background K+ channels such as TASK-1 and TASK-3, members of two-pore domain K+ (K2P) channel family, express and contribute to extracellular acidification-induced responses in dorsal root ganglia (DRG) neurons. However, it has remained to address whether other acid-sensitive background K+ channels are functionally expressed in DRG neurons. Here we characterized biophysical and pharmacological properties of a novel acid-sensitive background K+ channel in DRG neurons isolated from neonatal rats. We recorded an 80-pS K+ channel with a weak inward rectification current-voltage relationship in cell-attached patches in 150mM KCl bath solution. The 80-pS K+ channel was inhibited by extracellular low pH (pHo 6.3). Interestingly, the channel was similar to TASK-2 cloned from mouse and rat in biophysical and pharmacological properties. However, extracellular alkaline condition which activates TASK-2 channel, failed to activate the 80-pS K+ channel. Lidocaine and quinine more inhibited the channel activity of 80-pS K+ channel than that of TASK-2 channel. Our results suggest that the acid-sensitive 80-pS K+ channels may regulate resting membrane potential and may play a critical role in various processes such as cell metabolism, pH, and pain sensation in DRG neurons.

Soluble microbial products (SMP) and soluble extracellular polymeric substances (EPS) from wastewater sludge

Laspidou and Rittmann (Water Research 36:2711-2720, 2002) proposed that the soluble extracellular polymeric substances (EPS) are identical to soluble microbial products (SMP) in sludge liquor. In this paper, we compared the physicochemical characteristics of the SMP and soluble EPS from original and aerobically or anaerobically digested wastewater sludge. The surface charges, particle sizes, residual turbidities of polyaluminum chloride (PACl) coagulated supernatant, and chemical compositions of the SMP and soluble EPS containing suspensions were used as comparison index. Experimental results revealed that the particles in SMP and soluble EPS fractions extracted from original wastewater sludge, before and after digestion, were not identical in all physicochemical characteristics herein measured. The current test cannot support the proposal by Laspidou and Rittmann (Water Research 36:2711-2720, 2002) that SMP is identical to the soluble EPS from a wastewater sludge.

An endogenous acid-sensitive K+ channel expressed in COS-7 cells

COS-7 cells originally isolated from monkey kidney and used in many transfection studies were found to express a background K+ channel and therefore, its biophysical and pharmacological properties were examined. In cell-attached patches, a 32-pS K+ channel with a linear current-voltage relationship could be recorded. The open probability was highly voltage-dependent, with greater channel activity at depolarized potentials. The channel was markedly sensitive to changes in extracellular pH (pH(o)), showing a 70+/-10% inhibition by changing the pH(o) from 7.3 to 6.3. Arachidonic acid (5 microM) augmented channel activity 12-fold. Applying negative pressure (-40 mmHg) to the membrane patch also increased channel activity by 4-fold. These results show that COS-7 cells express a K+ channel with unique properties that must be considered when using these cells as transfection system.

Acetylcholine induces Ca 2+ oscillations via m3/m4 muscarinic receptors in the mouse oocyte

Changes in intracellular Ca2+ concentration are required for the activation of mammalian oocytes. They are caused mainly by Ca2+ release from the endoplasmic reticulum (ER) via Ins P3 receptors (Ins P3R). Several studies have reported that acetylcholine (ACh) is capable of triggering early activation events in mouse oocytes over-expressed with the m1 muscarinic ACh receptor (m1AChR). Here we examined which subtypes of the mAChR (m1 to m4) are involved in the generation of Ca2+ oscillations in native mouse oocytes. ACh (10 microM) elicited regular Ca2+ oscillations similar to those induced by sperm in their temporal characteristics. The Ca2+ oscillations were abolished by application with atropine, the mAChR inhibitor. Within 1 min after treatment of ACh, intracellular Fluo-3 fluorescence intensity increased from 794+/-119 to 2023+/-755 (increase to 250% of original value), indicating a strong rise of cytosolic Ca2+ concentration. 4-DAMP mustard and Tropicamide, specific antagonists of m3AChR and m4AChR, completely abolished ACh-induced Ca2+ oscillations. In the ovulated oocytes, the expression of m3/m4 AChR was clearly detected by RT-PCR analysis. Furthermore, ACh-induced Ca2+ oscillations were also abolished or decreased by PLC inhibitors (U73122 or D609) and an Ins P3-receptor antagonist (xestospongin C), confirming that ACh generates Ca2+ oscillations via the PLC-Ins P3 (PI) pathway. These results strongly suggest that m3/m4AChR is coupled to the generation of Ca2+ oscillations mainly via the PI pathway in mouse oocytes.

In vitro anti-proliferative effect of 1,2,3,4,6-penta-O-galloyl-beta-D-glucose on human hepatocellular carcinoma cell line, SK-HEP-1 cells

The root of Paeonia suffruticosa ANDREWS is an important Chinese crude drug used in many traditional prescriptions. 1,2,3,4,6-penta-O-galloyl-beta-D-glucose (PGG), a major component of this crude drug, was found to exhibit in vitro growth-inhibiting effect on human hepatocellular carcinoma cell line, SK-HEP-1 cells. The growth-inhibitory effect was related to the ability of PGG not only to cause a G(0)/G(1) phase arrest but also to suppress the activation of nuclear factor-kappa B. Neither apoptosis nor necrosis was observed in the cells treated with PGG. These findings suggest that PGG could be a candidate for developing a low-toxic anticancer agent.

[Differentiation of human hepatocarcinoma SMMC-7721 cells induced by HMBA]

In this paper, the effects of HMBA on the differentiation of human hepatocarcinoma cell line SMMC-7721 were investigated. After treated with 5 mmol/L HMBA, the proliferation of SMMC-7721 cells was inhibited remarkably, the cell growth inhibitory rate amounted to 64.14%, the cell mitotic index was declined by 53.88%. Light microscopy and transmission electron microscopy showed that the morphology and ultrastructure of the cells treated with HMBA undergone restorational alteration. Cytochemistry and immunocytochemistry assay revealed that the activities of gamma-GT declined and the levels of AFP and PCNA downregulated while the activity of TAT increased significantly after HMBA treatment. In the meantime, flow cytometry analysis showed that HMBA could arrest the cells in G0/G1 phase. The results showed that HMBA could effectively inhibit the proliferation, reverse the malignant morphology and ultrastructure, alter the levels of enzymes and antigens, arrest the cells in G0/G1, and induce the differentiation of human hepatocarcinoma SMMC-7721 cells in vitro.

Mistletoe lectin synergizes with paclitaxel in human SK-hep1 hepatocarcinoma cells

The effect of mistletoe lectin I (ML-I), an inhibitor of ribosomal protein synthesis, on the in vitro cytotoxicity of a clinically important anticancer drug, paclitaxel, was studied on cultured human hepatocarcinoma SK-Hep1 cells using the microculture tetrazolium test. The interaction between these two agents was analyzed for true synergism using the ED50 isobologram. Synergism was observed in the simultaneous treatment of the cells with ML-I in combination with paclitaxel. In addition, 24-h exposure of the cells to a non-toxic dose of ML-I and lower toxic doses of paclitaxel in combination resulted in apoptotic cell death, as observed by agarose-gel electrophoresis of low-molecular-weight DNA and DNA flow cytometry. Thus, the results presented here indicate the potential clinical usefulness of ML-I combination therapy with paclitaxel.

Metschnikowia koreensis sp. nov., a novel yeast species isolated from flowers in Korea

A novel ascomycetous yeast was isolated from flowers of Lilium sp. and Ipomoea sp. in Korea. The name Metschnikowia koreensis sp. nov. (type strain SG99-34T = CBS 8854T = KCTC 7998T) is proposed for this novel species based on comparative sequence analyses of the D1/D2 domain of 26S rDNA and phenotypic characteristics.

Protective effects of Orostachys japonicus A. Berger (Crassulaceae) on H2O2-induced apoptosis in GT1-1 mouse hypothalamic neuronal cell line

Oxidative stress is a major cause of neurodegenerative diseases, so the protection of neuronal cells from reactive oxygen species can be beneficial for the prevention and treatment of these diseases. Methanol extract of Orostachys japonicus A. Berger (Crassulaceae), a traditional oriental medical herb, was shown to have a protective effect on H2O2-induced apoptosis in GT1-1 mouse hypothalamic neuronal cell line which was detected by flow cytometry after propidium iodide staining. Among fractions of O. japonicus, chloroform fraction had the highest protective effect, and water fraction had no protective effect suggesting that the active ingredients might be hydrophobic compounds.

Regulation of atrial muscarinic K+ channel activity by a cytosolic protein via G protein-independent pathway

Rapid desensitization of the muscarinic K+ current (KACh current) is observed in cell-attached patches with 10 microM acetylcholine in the pipette. When inside-out patches were formed within approximately 1 s after formation of cell-attached patches and GTP was applied to the cytoplasmic side of the membrane, desensitization was not observed, indicating that a cytosolic factor mediated the desensitization. Applying the atrial cytosolic extract directly to the cytoplasmic side of such inside-out patches elicited a rapid desensitization of the KACh current. ATP (1-4 mM) reversed this effect of the cytosol and reverted the KACh channel to the undesensitized state. These effects of ATP and cytosol on the KACh channel could occur in the absence of GTP or in the presence of 100 microM guanosine 5'-O-(3-thiotriphosphate), indicating that G protein was not involved. Treatment of the cytosol with proteases (trypsin, chymotrypsin, bacterial protease) or heat denaturation abolished the effect of the cytosol on the KACh channel kinetics, indicating that the cytosolic factor was a protein. Functional assay of the fractions collected from gel filtration column indicated that the molecular mass of the native protein was 95-130 kDa. We conclude that a large cytosolic protein mediates the rapid desensitization of the KACh channel current via a G protein-independent pathway.

Rapid increase in deep supercooling of xylem parenchyma

Malus pumila Mill. twigs were collected from September through December and stored at 5 degrees C until the low temperature exotherms of the xylem were determined by differential thermal analysis. During the differential thermal analysis, cooling was interrupted, and temperatures of 5 to -18 degrees C were held for 0.4 to 10 hours before cooling to -50 degrees C was resumed. Control twigs were cooled to -50 degrees C without interruption. Holding the twigs at 1.3 to -5 degrees C shifted the start of the low temperature exotherm from about -20 to -30 degrees C. Slightly higher (2.6 degrees C) and lower (-10 degrees C) temperatures were occasionally effective. The shift began within 20 to 30 minutes and increased progressively to 150 minutes. The acclimation was reversibly inhibited by N(2) atmosphere.

Units of freezing of deep supercooled water in woody xylem

The low temperature exotherms (LTE) of 1-year-old twigs of Haralson apple (Malus pumila Mill.), shagbark hickory (Carya ovata [Mill.] K. Koch), green ash (Fraxinus pennsylvanica Marsh), honey locust (Gleditsia triacanthos L.), American chestnut (Castanea dentata [Marsh] Borkh.), and red oak (Quercus rubra L.) were determined by differential thermal analysis (DTA). In one type of experiment freezing during a DTA experiment was halted for up to 2.5 hours after part of the supercooled water had frozen at temperatures between -25 and -42 C. Upon resumption of cooling the freezing started within 2 C of the stopping temperature. In a second type of experiment living and dead cells were microscopically observed in the same ray after partial freezing in the DTA apparatus. In another experiment, the LTE persisted even after tangential and radial sectioning of the twig to 0.13 millimeters. In a final experiment the LTE of a single multiseriate ray of red oak had the same shape as the LTE of wood with many uniseriate rays.These experiments confirm that the deep supercooled water in woody xylem or pith freezes in numerous independent events over a span of as much as 20 C. The units which freeze in an event are single cells or small groups of cells. Ice grows very slowly if at all from these units, and water moves very slowly from unfrozen cells to frozen ones. Deep supercooling of ray parenchyma does not require an intact ray.

Effects of kinetin and root tip removal on exudation and potassium (rubidium) transport in roots of honey locust

Exudation, (86)Rb transport, and water permeability were examined in excised roots of honey locust (Gleditsia triacanthos L.) treated by removing the tip 2 mm (tip-cut 2 mm) or tip 8 mm of the root, or by adding kinetin, or by both treatments. Tip removal increased the rate of exudation. Kinetin, 5 x 10(-6)m, inhibited exudation and Rb transport in tip-cut 2-mm roots; the inhibition was reversible. Kinetin inhibition of exudation was initially associated with lower K(Rb) transport and later with decreases in both ion transport and water permeability. Exudation was also inhibited at 10(-10) to 10(-7)m kinetin. Exudation from roots with intact tips was not altered by kinetin until after about 24 hours. Light during the exudation period had no significant (95%) influence on rate of exudation during the first 24 hours whether root tips were cut or kinetin applied.The results suggest the involvement of the root tip in regulating exudation in other parts of the root. This regulation might occur through cytokinin control of water permeability and the rate of ion transport.