Biomedical subjects

K Furukawa

Publications and source records attributed to K Furukawa.

At least 19 recordsLinked to original sources

PubMed1995

The effects of the site-directed removal of N-glycosylation sites from beta-1,4-N-acetylgalactosaminyltransferase on its function.

The amino acid sequence deduced from the cloned human cDNA of beta-1,4-N-acetylgalactosaminyltransferase (GalNAc-T; EC 2.4.1.92) gene predicted three potential sites for N-linked glycosylation. Although many glycosyltransferases isolated contain from 2 to 6 N-glycosylation sites, their significance has not been adequately demonstrated. To clarify the roles of N-glycosylation in GalNAc-T function, we generated a series of mutant cDNAs, in which some or all of the glycosylation recognition sites were eliminated by polymerase chain reaction (PCR)-mediated site-directed mutagenesis. Using transcription/translation in vitro, we confirmed that all potential N-glycosylation sites could be used. Although cell lines transfected with mutant cDNAs showed equivalent levels of GalNAc beta 1-->4(NeuAc alpha 2-->3)Gal beta 1-->4Glc-Cer (GM2) to that of the wild-type, the extracts from mutant cDNA transfectants demonstrated lower enzyme activity than in the wild-type. The decrease in enzyme activity was more evident as the number of deglycosylated sites increased, with about 90% decrease in a totally deglycosylated mutant. The enzyme kinetics analysis revealed no significant change of Km among wild-type and mutant cDNA products. The intracellular localization of GalNAc-T expressed in transfectants with wild-type or mutant cDNAs also showed a similar perinuclear pattern (Golgi pattern). These results suggest that N-linked carbohydrates on GalNAc-T are required for regulating the stability of the enzyme structure.

Animals↗

PubMed1995

Analysis of melanoma cells stably transfected with beta 1,4GalNAc transferase (GM2/GD2 synthase) cDNA: relative glycosyltransferase levels play a dominant role in determining ganglioside expression.

Previous studies (Y. Nagata, S. Yamashiro, J. Yodoi, K. O. Lloyd, H. Shiku, and K. Furukawa (1992) J. Biol. Chem. 267, 12082-12089) had isolated a putative cDNA coding for beta 1,4 N-acetylgalactosaminyltransferase (GM2/GD2 synthase) and demonstrated the presence of GM2 and/or GD2 gangliosides in melanoma cell lines stably transfected with this gene. We have now measured the levels of glycosyltransferase activities and mRNA levels in five transfected cell lines in comparison with their parent cell lines (mouse melanoma B16 and human melanoma MeWo). Membrane preparations from the transfected cell lines demonstrated de novo synthesis of GM2 or GD2 in in vitro assays using GM3 or GD3, respectively, as ganglioside acceptors. The enzyme levels, however, varied considerably among the different transfectants, as did the mRNA levels for the beta 1,4 Gal-NAc-transferase. The effect of the transfected gene on levels of preexisting glycosyltransferases involved in ganglioside biosynthesis was also measured and the ganglioside composition of the cell lines was determined. The level of beta 1,4 GalNAc-transferase expressed in the different cell lines was found to dramatically influence the overall ganglioside composition of the cell. In the transfected cell line with the highest levels of the transferase, for example, biosynthesis was almost completely redirected away from the b pathway to the a pathway with the resulting expression of only GM2. These data from this family of related cell lines clearly demonstrate the primary roles that relative glycosyltransferase levels play in determining the ganglioside composition of cells.

Animals↗

PubMed1995

[3H]9-Methyl-7-bromoeudistomin D, a caffeine-like powerful Ca2+ releaser, binds to caffeine-binding sites distinct from the ryanodine receptors in brain microsomes.

[3H]9-Methyl-7-bromoeudistomin D ([3H]MBED), the most powerful Ca2+ releaser from sarcoplasmic reticulum, specifically bound to the brain microsomes. Caffeine competitively inhibited [3H]MBED binding. [3H]MBED binding was markedly blocked by procaine, whereas that was enhanced by adenosine-5'-(beta,gamma-methylene)triphosphate. The Bmax value was 170 times more than that of [3H]ryanodine binding. The profile of sucrose-density gradient centrifugation of solubilized microsomes indicated that [3H]MBED binding protein was different from [3H]ryanodine binding protein. These results suggest that there are MBED/caffeine-binding sites in brain that are distinct from the ryanodine receptor and that MBED becomes an essential molecular probe for characterizing caffeine-binding protein in the central nervous system.

Adenosine Triphosphate↗

PubMed1995

Xestoquinone activates skeletal muscle actomyosin ATPase by modification of the specific sulfhydryl group in the myosin head probably distinct from sulfhydryl groups SH1 and SH2.

Xestoquinone isolated from a sea sponge Xestospongia sapra inhibited both Ca2+ and K(+)-(EDTA) ATPase of skeletal muscle myosin. The inhibition was abolished in the presence of dithiothreitol. Xestoquinone reacted with 2-mercaptoethanol, a sulfhydryl (SH) compound. Unlike N-ethylmaleimide, a well-known SH reagent, modification of 2 mol of SH groups per myosin by xestoquinone caused a marked increase in the actomyosin ATPase activity. Kinetical analysis of stimulatory effects of xestoquinone indicates a decrease in the actin concentrations which gives half of the maximum velocity (Vmax) of actomyosin ATPase reaction without affecting the Vmax, suggesting an increase in the affinity of myosin for actin. N-Ethylmaleimide can still modify both the SH1 and SH2 groups after modification of 2 mol of SH groups by xestoquinone. Xestoquinone modified myosin SH groups which caused changes in the tryptophan fluorescence intensity and circular dichroism. These results suggest that xestoquinone modifies the specific SH groups in myosin distinct from SH1 and SH2, resulting in activation of actomyosin ATPase. It is also suggested that xestoquinone strengthens the interaction between actin and myosin through conformational change in the myosin molecule.

Actins↗

PubMed1995

Tumor necrosis factors alpha and beta protect neurons against amyloid beta-peptide toxicity: evidence for involvement of a kappa B-binding factor and attenuation of peroxide and Ca2+ accumulation.

In Alzheimer disease (AD) the amyloid beta-peptide (A beta) accumulates in plaques in the brain. A beta can be neurotoxic by a mechanism involving induction of reactive oxygen species (ROS) and elevation of intracellular free calcium levels ([Ca2+]i). In light of evidence for an inflammatory response in the brain in AD and reports of increased levels of tumor necrosis factor (TNF) in AD brain we tested the hypothesis that TNFs affect neuronal vulnerability to A beta. A beta-(25-35) and A beta-(1-40) induced neuronal degeneration in a concentration- and time-dependent manner. Pretreatment of cultures for 24 hr with TNF-beta or TNF-alpha resulted in significant attenuation of A beta-induced neuronal degeneration. Accumulation of peroxides induced in neurons by A beta was significantly attenuated in TNF-pretreated cultures, and TNFs protected neurons against iron toxicity, suggesting that TNFs induce antioxidant pathways. The [Ca2+]i response to glutamate (quantified by fura-2 imaging) was markedly potentiated in neurons exposed to A beta, and this action of A beta was suppressed in cultures pretreated with TNFs. Electrophoretic mobility-shift assays demonstrated an induction of a kappa beta-binding activity in hippocampal cells exposed to TNFs. Exposure of cultures to I kappa B (MAD3) antisense oligonucleotides, a manipulation designed to induce NF-kappa B, mimicked the protection by TNFs. These data suggest that TNFs protect hippocampal neurons against A beta toxicity by suppressing accumulation of ROS and Ca2+ and that kappa B-dependent transcription is sufficient to mediate these effects. A modulatory role for TNF in the neurodegenerative process in AD is proposed.

Amyloid beta-Peptides↗

PubMed1995

Effects of N-3554S, a polyprenyl phosphate, on B16-F10 mouse melanoma cells.

N-3554S, an optically active S-isomer of alpha-dihydrodecaprenyl phosphate, reduced the tumorigenicity of cultured B16-F10 mouse melanoma cells probably by affecting protein N-glycosylation. Accordingly, membrane glycoprotein samples were prepared from the melanoma cells cultured with or without N-3554S, and amounts and structures of N-linked sugar chains were determined. Analyses of the N-linked oligosaccharides released by hydrazinolysis from these samples and reduced with NaB3H4 revealed that the N-3554S-treated cells contain 1.5-1.8 times as much oligosaccharides as the control cells, and the relative amounts of high-mannose-type and bi-, tri- and tetra-antennary complex-type sugar chains are almost the same between two samples. Western blot analysis, however, showed that binding of L-PHA, which binds to oligosaccharides with the GlcNAc beta 1-->6(GlcNAc beta 1-->2)Man structure, is significantly reduced in 90 K, 96 K, 140 K, 155 K and 180 K glycoproteins in N-3554S-treated cells. Immunoblot analysis showed that the 140 K glycoprotein could be a fibronectin receptor. It was also shown that N-3554S treatment enhances the adhesiveness of the cells to fibronectin. These results indicate that N-3554S affects N-glycosylation of membrane glycoproteins and alters the cell surface properties of B16-F10 cells.

Animals↗

PubMed1995

A bovine IgG heavy chain contains N-acetylgalactosaminylated N-linked sugar chains.

A 56K protein co-purified with bovine milk fat globule membrane (MFGM) proteins bound to Wisteria floribunda agglutinin (WFA) like most MFGM glycoproteins. Treatment with N-glycanase or beta-N-acetylhexosaminidase abolished the lectin binding to the protein. Amino acid sequence and immunoblot analyses revealed that the 56K protein is an IgG heavy chain. Lectin column chromatography of the oligosaccharides released by hydrazinolysis from the purified IgG heavy chains revealed that 0.08% of the total N-linked sugar chains bind to a WFA-agarose column, suggesting that they contain the beta-N-acetylgalactosaminylated structure.

Acetylgalactosamine↗

PubMed1995

Two isotypes of murine nm23/nucleoside diphosphate kinase, nm23-M1 and nm23-M2, are involved in metastatic suppression of a murine melanoma line.

A series of sublines of a murine melanoma B16 of C57BL/6 origin were established and examined regarding their metastatic capacity and expression of nm23. The number of pulmonary metastases developed by these sublines was inversely correlated with the expression of two isotypes of nm23, nm23-M1 and nm23-M2. The cDNAs of nm23-M1, nm23-M2, and a combination of both were transfected into the highly metastatic melanoma subline FE7, with low nm23 expression. FE7 transfectants of any of these cDNAs expressed transfected genes, and their metastatic capacity was suppressed when compared with parental FE7 or FE7 transfected with a control neo gene. These cell lines, however, did not change in terms of in vitro growth in the presence of 3 or 10% fetal bovine serum and in vivo growth when injected s.c. into C57BL/6-nu/nu mice. Similar experiments were also performed using FE7 transfectants of human nm23 genes. Transfectants of nm23-H1, nm23-H2, and their combination did not present altered metastatic potential. These findings indicated that two murine isotypes of nm23 but not those of humans are intimately related with the suppression of metastasis in the murine body.

Animals↗

PubMed1995

Cloning of a cDNA for lamina-associated polypeptide 2 (LAP2) and identification of regions that specify targeting to the nuclear envelope.

Lamina-associated polypeptide 2 (LAP2) is an integral membrane protein of the inner nuclear membrane, which binds directly to both lamin B1 and chromosomes in a mitotic phosphorylation-regulated manner. The biochemical and physiological properties of LAP2 suggest an important role in nuclear envelope re-assembly at the end of mitosis and/or anchoring of the nuclear lamina and interphase chromosomes to the nuclear envelope. We describe the cDNA cloning of LAP2 and characterization of its membrane topology and targeting to the nuclear envelope. The LAP2 cDNA sequence predicts a protein of 452 amino acids, containing a large hydrophilic domain with several potential cdc2 kinase phosphorylation sites and a single putative membrane-spanning sequence at residues 410-433. Immunogold localization of an LAP2 epitope in isolated nuclear envelopes indicates that the large amino-terminal hydrophilic domain (residues 1-409) is exposed to the nucleoplasm. By expressing deletion mutants of LAP2 in cultured cells, we have identified multiple regions in its nucleoplasmic domain that promote localization at the nuclear envelope. These data suggest that targeting of LAP2 to the nuclear envelope is mediated by cooperative interactions with multiple binding sites at the inner nuclear membrane.

Amino Acid Sequence↗

PubMed1995

Substrate specificity of beta 1,4-N-acetylgalactosaminyltransferase in vitro and in cDNA-transfected cells. GM2/GD2 synthase efficiently generates asialo-GM2 in certain cells.

The substrate specificity of beta 1,4-N-acetylgalactosaminyltransferase has been analyzed using a fusion enzyme which consisted of the catalytic domain of the enzyme and the IgG binding domain of protein A, and also by extracts from cDNA transfectants. Both enzyme sources were capable of producing not only GM2 and GD2, but also asialo-GM2, GalNAc-sialylparagloboside, and Gal-NAc-GD1a from appropriate acceptors, although the efficiencies were at most 1-3% of those of GM2/GD2. The biological significance of these low specificities was studied with transient and stable transfectant cells. From the results of transient expression of the cDNA, asialo-GM2 expression appeared to inversely correlate with GM2 synthase levels in those lines. Consequently, GM2 seemed to be preferentially synthesized when both GM3 and lactosylceramide are available, and asialo-GM2 is synthesized in the absence of GM3 synthesis. However, the results of double immunostaining of CHO transfectants with anti-GM2 and anti-asialo-GM2 antibodies indicated that another factor may be involved in asialo-GM2 synthesis. From the in vitro assay using mixed acceptors, it was concluded that the presence of certain levels of GM2 might enhance the asialo-GM2 synthesis. These results suggest that even acceptors showing low efficiencies in vitro might be used in certain cells depending on the availability of precursors, expression levels of other gangliosides, as well as the kinetic properties of the enzyme, and the compartmentation of the glycosylation machineries in the cells.

Animals↗

PubMed1995

The effects of dietary fiber from Lagenaria scineraria (yugao-melon) on colonic carcinogenesis in mice.

BACKGROUND: The increasing trend of colon cancer in Japan is attributed to changes in dietary habits, that is, increased amounts of fat and decreased amounts of fiber in the diet. The effects of Japanese dietary fiber from Lagenaria scineraria (yugao-melon) on colonic carcinogenesis in mice were examined. METHODS: Eighteen ICR mice in each group were fed with either a basal diet or a diet containing 5%, 10%, or 20% of yugao powder for 35 weeks. All the mice received a weekly intraperitoneal injection of 1,2-dimethylhydrazine (DMH), 10 mg/kg body weight for 10 weeks. The effects of yugao powder on the mucosal and luminal variables involved in colonic carcinogenesis were then compared with those of wheat bran in the mice without any carcinogen treatment. RESULTS: The incidence of colon tumors (adenocarcinomas) was lower in the yugao powder diet groups than in the basal diet group at week 35 (24% vs. 50%, P < 0.05). The bile acid concentration in the colon was reduced in all the fiber diet groups except for the 5% yugao powder diet group. The colonic luminal pH acidified as yugao powder contents also increased in the yugao powder diet groups. The findings on the colonic short chain fatty acids, microflora, and mucosal fatty acids and ornithine decarboxylase activity were all inconsistent with a tendency to either develop or to inhibit carcinogenesis in both the fiber diet groups. CONCLUSIONS: Dietary fiber from yugao-melon suppressed DMH-induced colonic carcinogenesis in mice by lowering the bile acid concentration and pH in the colon. The results of the luminal and mucosal variables examined also suggested that the mechanisms of action of yugao powder against colonic carcinogenesis differed from those of wheat brain.

Adenocarcinoma↗

PubMed1995

Enhanced expression of GM2/GD2 synthase mRNA in human gastrointestinal cancer.

BACKGROUND: The content of the GM2 ganglioside and the activity of UDP-GalNAc: GM3 beta-1,4N-acetylgalactosaminyltransferase (beta-1,4GalNAcT), which synthesizes GM2, increased in gastric cancer tissues and gastric cancer cell lines as compared with that in normal gastric mucosa. METHODS: Expression of beta-1,4GalNAcT mRNA and a concentration of GM2 in the human gastrointestinal tissues were examined. Beta-1,4GalNAcT mRNA in human surgical specimens, which was not detectable with Northern blotting because of the paucity of absolute amounts expressed, was detected with competitive reverse transcription-polymerase chain reaction (PCR) method using an internal standard cRNA that could be amplified by the same primers as target mRNA in PCR. The quantification of GM2 was examined using immunostaining of thin-layer chromatography. RESULTS: In 10 of 10 gastric carcinomas and 6 of 13 colonic carcinomas, mRNA expression was more enhanced than that in the normal mucosa of each patient. The alteration of GM2 content in carcinoma from normal tissue generally was correlated to the change in the expression of beta-1,4GalNAcT mRNA with a few exceptions. One gastric cancer sample had a higher level of mRNA with a lower GM2 content than the corresponding normal tissue, and two colonic carcinoma tissue specimens had a lower level of mRNA with a higher GM2 content. CONCLUSIONS: These results suggest that expression of the beta-1,4GalNAcT gene is a key step in the molecular mechanisms underlying the regulation of cancer-associated GM2 expression in the stomach and the colon.

Adenocarcinoma↗

PubMed1995

p53 gene mutations in early colorectal carcinoma. De novo vs. adenoma-carcinoma sequence.

p53 gene mutations in early and advanced colorectal cancer were detected by PCR-SSCP analysis. Early colorectal cancer was classified into de novo cancer and polyp-forming cancer, respectively, according to morphology and presence of adenomatous components. A total of 94 paraffin-embedded tissue specimens from patients with colorectal cancer were analysed. p53 gene mutations were detected in 40.0% (12/30) of de novo cancer, 36.7% (11/30) of polyp-forming cancer, and 44% (15/34) of advanced cancer. p53 mutations were detected at a high frequency in both types of early colorectal cancer as well as in advanced cancer. No correlations were found between p53 mutations and clinicopathological data. Our data suggest that the p53 gene mutations occurred in the early colorectal cancer stage of carcinogenesis regardless of the pathway.

Adenoma↗

PubMed1995

Structure-activity relationship of bromoeudistomin D, a powerful Ca2+ releaser in skeletal muscle sarcoplasmic reticulum.

Bromoeudistomin D and 9-methyl-7-bromoeudistomin D which have a beta-carboline skeleton are powerful Ca2+ releasers from skeletal muscle sarcoplasmic reticulum exhibiting caffeine-like properties. We examined the effects of bromoeudistomin D analogues on Ca(2+)-induced Ca2+ release from skeletal muscle sarcoplasmic reticulum. Among bromoeudistomin D analogues, the Ca(2+)-releasing activities of carboline derivatives were higher than those of carbazole derivatives, suggesting that a carboline skeleton is significantly important for the manifestation of Ca(2+)-releasing activity and Ca2+ sensitivity of Ca(2+)-induced Ca2+ release. On the contrary, the analogues which have a carbazole skeleton and bromine at C-6 inhibit both Ca(2+)- and caffeine-induced Ca2+ release. 9-Methyl-substitution of the analogue elevated its Ca(2+)-releasing activity. Moreover, there is a close correlation between the enhancement of [3H]ryanodine binding to sarcoplasmic reticulum by the analogues and the activation of Ca2+ release by them. Bromoudistomin D analogues may provide valuable information about the structure-function relationship of the ryanodine receptor/Ca2+ release channels in skeletal muscle sarcoplasmic reticulum.

Animals↗

PubMed1995

Induction of murine gamma delta T cells cytotoxic for xenogeneic rat cells.

C57BL/6 mice deprived or nondeprived of CD4+ and CD8+ T cells by mAbs were challenged with a rat T cell line, W7TM-1. Spleen cells obtained from CD4- and CD8-depleted animals rejecting W7TM-1 were examined by cytofluorometry, which demonstrated the presence of highly increased gamma delta type CD4-CD8- T cell population (30 to 50% of entire T cells). In vitro sensitization of these spleen cells with W7TM-1 generated a mixture of gamma delta and alpha beta type CD4-CD8- CTL for W7TM-1. Repeated stimulation of these cells with W7TM-1 resulted in a gamma delta-type T cell population with more than 95% purity by day 45. In contrast, alpha beta type CD8+ CTL for W7TM-1 were induced from mice nondeprived of CD4+ and CD8+ T cells. Both gamma delta-type CD4-CD8- CTL and alpha beta type CD8+ CTL were cytotoxic for rat cells in a species-specific manner. However, only reactivity of gamma delta type CD4-CD8- CTL, but not alpha beta type CTL, was inhibited by a mAb for TCR-gamma delta. The gamma delta type CD4-CD8- CTL clones were also prepared from spleen cells derived from CD4- and CD8-depleted mice. They were also reactive for xenogeneic cells in a species-specific manner. Spleen cells derived from CD4- and CD8-depleted mice rejecting the whole-layer rat skin grafts were in vitro sensitized with rat spleen cells, which also generated gamma delta type CD4-CD8- CTL specific for rat cells. V gamma 1 was detected as a major V gamma gene expressed in this gamma delta population by reverse transcriptase-PCR. Cytotoxicity for xenogeneic cells may represent one of major function of gamma delta T cells.

Animals↗

PubMed1995

[A case of polyglandular autoimmune syndrome (PGA) type 1 complicated with slowly progressive IDDM].

A case of an 18-year-old female with polyglandular autoimmune syndrome (PGA) type 1 complicated by slowly progressive IDDM was described. She had epilepsy at the age of 5, and mucocutaneous candidiasis and hypoparathyroidism at 7 years. At the age of 18, the patient noticed thirst and body weight loss. On admission, she had uneven teeth and chronic mucocutaneous candidiasis. Plasma blood glucose was 312 mg/dl without ketosis, hemoglobin Alc 9.1%, serum calcium 3.5 mEq/l, serum phosphorus 6.0 mg/dl. A CT scan of her brain revealed calcification in the bilateral basal ganglia. Serum intact PTH was less than 10 pg/ml. Ellsworth-Howard's test showed hyperresponsiveness in the secretion of urinary phosphorus and cyclic-AMP. Other endocrinological studies showed no abnormality except for mild hyporesponsiveness in the secretion of urinary C-peptide (39.6 mu g/day). After admission, she was initially treated with diet alone with positive islet cell antibody (ICA). Three months later she was treated with low dose insulin, and ICA became negative. Then 5 months later it became positive again. Sixteen months later she had IDDM with positive ICA and without the secretion of urinary C-peptide. On the basis of these results, we diagnosed this case as PGA type 1 with the manifestations of hypoparathyroidism, chronic mucocutaneous candidiasis and slowly progressive IDDM. This is the second case report in Japan about PGA type 1. Furthermore, this case demonstrates for the first time in Japan that slowly progressive IDDM is complicated by PGA type 1. The patient had this HLA typing: A 24(9), BW52(5), BW60(40), CW3, DR2, DRW12, DQW7. More investigation is necessary to clarify the mechanism of PGA type 1.

Adolescent↗

PubMed1995

T cell receptor-mediated stimulation of mouse thymocytes induces up-regulation of the GM2/GD2 synthase gene.

cDNA clones of the mouse GM2/GD2 synthase (EC 2.4.1.92) gene were isolated, and their analyses revealed that the protein has a type II transmembrane structure with 533 amino acids, which was very similar to the human homolog except for the mRNA size. The mRNA level in thymocytes dramatically increased after treatment with anti-CD3 monoclonal antibody, whereas it was not elevated when treated with prostaglandin E2. In situ hybridization showed an elevation of mRNA levels in medullar thymocytes, suggesting that T cell receptor-mediated signaling induces up-regulation of the GM2/GD2 synthase gene in mature thymocytes.

Amino Acid Sequence↗

PubMed1995

Evidence that actin depolymerization protects hippocampal neurons against excitotoxicity by stabilizing [Ca2+]i.

Calcium influx through glutamate receptors and voltage-dependent channels mediates an array of functional and structural responses in neurons. However, unrestrained Ca2+ influx can injure and kill neurons; a mechanism implicated in both acute and chronic neurodegenerative disorders. Data reported here indicate that depolymerization of actin filaments can stabilize intracellular free calcium levels ([Ca2+]i) and protect hippocampal neurons against excitotoxic injury. Studies with fluorescein-labeled phalloidin showed that cytochalasin D and glutamate each induced actin filament depolymerization. The microfilament-disrupting agent cytochalasin D protected cultured rat hippocampal neurons against glutamate toxicity, whereas the actin filament-stabilizing agent jasplakinolide potentiated glutamate toxicity. The microtubule-disrupting agent colchicine was ineffective in protecting neurons against glutamate toxicity. Cytochalasin D did not protect neurons against calcium ionophore toxicity or iron toxicity, indicating that its actions were not due to nonspecific effects on Ca2+ or free radical metabolism. Cytochalasin D markedly attenuated kainate-induced damage to hippocampus of adult rats, suggesting an excitoprotective role for actin depolymerization in vivo. Elevations of [Ca2+]i induced by glutamate were attenuated in cultured hippocampal neurons pretreated with cytochalasin D and potentiated in neurons pretreated with jasplakinolide. The [Ca2+]i response to a Ca2+ ionophore was unaffected by cytochalasin D, suggesting that actin depolymerization reduced Ca2+ influx through membrane channels. Taken together with previous patch clamp data, our findings suggest that depolymerization of actin in response to Ca2+ influx may serve as a feedback mechanism to attenuate potentially toxic levels of Ca2+ influx.

Actins↗