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K Imoto

Publications and source records attributed to K Imoto.

At least 19 recordsLinked to original sources
PubMed1999

Direct alteration of the P/Q-type Ca2+ channel property by polyglutamine expansion in spinocerebellar ataxia 6.

Spinocerebellar ataxia 6 (SCA6) is caused by expansion of a polyglutamine stretch, encoded by a CAG trinucleotide repeat, in the human P/Q-type Ca(2+) channel alpha(1A) subunit. Although SCA6 shares common features with other neurodegenerative glutamine repeat disorders, the polyglutamine repeats in SCA6 are exceptionally small, ranging from 21 to 33. Because this size is too small to form insoluble aggregates that have been blamed for the cause of neurodegeneration, SCA6 is the disorder suitable for exploring the pathogenic mechanisms other than aggregate formation, whose universal role has been questioned. To characterize the pathogenic process of SCA6, we studied the effects of polyglutamine expansion on channel properties by analyzing currents flowing through the P/Q-type Ca(2+) channels with an expanded stretch of 24, 30, or 40 polyglutamines, recombinantly expressed in baby hamster kidney cells. Whereas the Ca(2+) channels with </=24 polyglutamines showed normal properties, the Ca(2+) channels with 30 or 40 polyglutamines exhibited an 8 mV hyperpolarizing shift in the voltage dependence of inactivation, which considerably reduces the available channel population at a resting membrane potential. The results suggest that polyglutamine expansion in SCA6 leads to neuronal death and cerebellar atrophy through reduction in Ca(2+) influx into Purkinje cells and other neurons. Besides the widely accepted notion that polyglutamine stretches exert toxic effects by forming aggregates, expanded polyglutamines directly alter functions of the affected gene product.

Animals↗
PubMed1999

Stability of the dimerization domain effects the cooperative DNA binding of short peptides.

The basic region peptide derived from the basic leucine zipper protein GCN4 bound specifically to the native GCN4 binding sequences in a dimeric form when the beta-cyclodextrin/adamantane dimerization domain was introduced at the C-terminus of the GCN4 basic region peptide. We describe here how the structure and stability of the dimerization domain affect the cooperative formation of the peptide dimer-DNA complex. The basic region peptides with five different guest molecules were synthesized, and their equilibrium dissociation constants with a peptide possessing beta-cyclodextrin were determined. These values, ranging from 1.3 to 15 microM, were used to estimate the stability of the complexes between the dimers with various guest/cyclodextrin dimerization domains and GCN4 target sequences. An efficient cooperative formation of the dimer complexes at the GCN4 binding sequence was observed when the adamantyl group was replaced with the norbornyl or noradamantyl group, but not with the cyclohexyl group that formed a beta-cyclodextrin complex with a stability that was 1 order of magnitude lower than that of the adamantyl group. Thus, cooperative formation of the stable dimer-DNA complex appeared to be effected by the stability of the dimerization domain. For the peptides that cooperatively formed dimer-DNA complexes, there was no linear correlation between the stability of the inclusion complex and that of the dimer-DNA complex. With the beta-cyclodextrin/adamantane dimerization domain, the basic region peptide dimer preferred to bind to a palindromic 5'-ATGACGTCAT-3' sequence over the sequence lacking the central G.C base pair and that with an additional G.C base pair in the middle. Changing the adamantyl group into a norbornyl group did not alter the preferential binding of the peptide dimers to the palindromic sequence, but slightly affected the selectivity of the dimer for other nonpalindromic sequences. The helical contents of the peptides in the DNA-bound dimer with the adamantyl group were decreased by reducing the stability of the dimer-DNA complex, which was possibly caused by deformation of the helical structure proximal to the dimerization domain.

Basic-Leucine Zipper Transcription Factors↗
PubMed1999

Tonic and phasic tetrodotoxin block of sodium channels with point mutations in the outer pore region.

Tonic and use-dependent block by tetrodotoxin (TTX) has been studied in cRNA-injected Xenopus oocytes expressing mutants W386Y, E945Q, D1426K, and D1717Q, of the outer-pore region of the rat brain IIA alpha-subunit of sodium channels. The various phenotypes are tonically half-blocked at TTX concentrations, IC50(t), that span a range of more than three orders of magnitude, from 4 nM in mutant D1426K to 11 microM in mutant D1717Q. When stimulated with repetitive depolarizing pulses at saturating frequencies, all channels showed a monoexponential increase in their TTX-binding affinity with time constants that span an equally wide range of values ([TTX] approximately IC50(t), from approximately 60 s for D1426K to approximately 30 ms for D1717Q) and are in most phenotypes roughly inversely proportional to IC50(t). In contrast, all phenotypes show the same approximately threefold increase in their TTX affinity under stimulation. The invariance of the free-energy difference between tonic and phasic configurations of the toxin-receptor complex, together with the extreme variability of phasic block kinetics, is fully consistent with the trapped-ion mechanism of use dependence suggested by and developed by. Using this model, we estimated for each phenotype both the second-order association rate constant, kon, and the first-order dissociation rate constant, koff, for TTX binding. Except for mutant E945Q, all phenotypes have roughly the same value of kon approximately 2 microM-1 s-1 and owe their large differences in IC50(t) to different koff values. However, a 60-fold reduction in kon is the main determinant of the low TTX sensitivity of mutant E945Q. This suggests that the carboxyl group of E945 occupies a much more external position in the pore vestibule than that of the homologous residue D1717.

Animals↗
PubMed1999

Evaluation of surgeries for rheumatoid shoulder based on the destruction pattern.

OBJECTIVE: To identify the optimal treatment of rheumatoid shoulder, we analyzed the clinical results of shoulder surgeries according to each type of shoulder destruction pattern. METHODS: Forty-seven shoulder surgeries for rheumatoid arthritis (18 arthroscopic synovectomies, 10 total shoulder replacements, 19 humeral head replacements) were assessed clinically and compared in regard to 5 different destruction patterns of rheumatoid shoulder (nonprogressive, arthrosis-like, erosive, collapse, and mutilating patterns). RESULTS: For nonprogressive-type shoulders, we were able to obtain both pain relief and range of motion (ROM) improvement with arthroscopic synovectomy. For erosive-type shoulders, we could obtain pain relief but no ROM improvement with synovectomy; and we obtained both pain relief and ROM improvement with prosthetic replacement. For the collapse-type shoulders, we could not obtain pain relief or ROM improvement with arthroscopic synovectomy, but did obtain pain relief with prosthetic replacement. For mutilating-type shoulders, we could obtain only pain relief with prosthetic replacement. The results of the various surgeries for rheumatoid shoulder were distinctly different depending on the shoulder destruction patterns. CONCLUSION: These findings could be of value for the selection of treatment, including a surgical procedure, for rheumatoid shoulders. For the nonprogressive-type and for erosive-type shoulders before bone destruction progresses, arthroscopic synovectomy should be selected. For erosive-type shoulders after bone destruction, for the collapse-type, and for mutilating-type shoulders, prosthetic replacement should be selected. In regard to the prosthetic replacement, the humeral component should be cemented because the incidence of migration in noncemented humeral component procedures was high.

Adult↗
PubMed1998

Single tottering mutations responsible for the neuropathic phenotype of the P-type calcium channel.

Recent genetic and molecular biological analyses have revealed many forms of inherited channelopathies. Homozygous ataxic mice, tottering (tg) and leaner (tgla) mice, have mutations in the P/Q-type Ca2+ channel alpha1A subunit gene. Although their clinical phenotypes, histological changes, and locations of gene mutations are known, it remains unclear what phenotypes the mutant Ca2+ channels manifest, or whether the altered channel properties are the primary consequence of the mutations. To address these questions, we have characterized the electrophysiological properties of Ca2+ channels in cerebellar Purkinje cells, where the P-type is the dominant Ca2+ channel, dissociated from the normal, tg, and tgla mice, and compared them with the properties of the wild-type and mutant alpha1A channels recombinantly expressed with the alpha2 and beta subunits in baby hamster kidney cells. The most striking feature of Ca2+ channel currents of mutant Purkinje cells was a marked reduction in current density, being reduced to approximately 60 and approximately 40% of control in tg and tgla mice, respectively, without changes of cell size. The Ca2+ channel currents in the tg Purkinje cells showed a relative increase in non-inactivating component in voltage-dependent inactivation. Besides the same change, those of the tgla mice showed a more distinct change in voltage dependence of activation and inactivation, being shifted in the depolarizing direction by approximately 10 mV, with a broader voltage dependence of inactivation. In the recombinant expression system, the tg channel with a missense mutation (P601L) and one form of the two possible tgla aberrant splicing products, tgla (short) channel, showed a significant reduction in current density, while the other form of the tgla channels, tgla (long), had a current density comparable to the normal control. On the other hand, the shift in voltage dependence of activation and inactivation was observed only for the tgla (long) channel. Comparison of properties of the native and recombinant mutant channels suggests that single tottering mutations are directly responsible for the neuropathic phenotypes of reduction in current density and deviations in gating behavior, which lead to neuronal death and cerebellar atrophy.

Animals↗
PubMed1998

Molecular cloning and functional characterization of a novel receptor-activated TRP Ca2+ channel from mouse brain.

Characterization of mammalian homologues of Drosophila TRP proteins, which induce light-activated Ca2+ conductance in photoreceptors, has been an important clue to understand molecular mechanisms underlying receptor-activated Ca2+ influx in vertebrate cells. We have here isolated cDNA that encodes a novel TRP homologue, TRP5, predominantly expressed in the brain. Recombinant expression of the TRP5 cDNA in human embryonic kidney cells dramatically potentiated extracellular Ca2+-dependent rises of intracellular Ca2+ concentration ([Ca2+]i) evoked by ATP. These [Ca2+]i transients were inhibited by SK&F96365, a blocker of receptor-activated Ca2+ entry, and by La3+. Expression of the TRP5 cDNA, however, did not significantly affect [Ca2+]i transients induced by thapsigargin, an inhibitor of endoplasmic reticulum Ca2+-ATPases. ATP stimulation of TRP5-transfected cells pretreated with thapsigargin to deplete internal Ca2+ stores caused intact extracellular Ca2+-dependent [Ca2+]i transients, whereas ATP suppressed [Ca2+]i in thapsigargin-pretreated control cells. Furthermore, in ATP-stimulated, TRP5-expressing cells, there was no significant correlation between Ca2+ release from the internal Ca2+ store and influx of extracellular Ca2+. Whole-cell mode of patch-clamp recording from TRP5-expressing cells demonstrated that ATP application induced a large inward current in the presence of extracellular Ca2+. Omission of Ca2+ from intrapipette solution abolished the current in TRP5-expressing cells, whereas 10 nM intrapipette Ca2+ was sufficient to support TRP5 activity triggered by ATP receptor stimulation. Permeability ratios estimated from the zero-current potentials of this current were PCa:PNa:PCs = 14.3:1. 5:1. Our findings suggest that TRP5 directs the formation of a Ca2+-selective ion channel activated by receptor stimulation through a pathway that involves Ca2+ but not depletion of Ca2+ store in mammalian cells.

Amino Acid Sequence↗
PubMed1998

Differential distribution of TRP Ca2+ channel isoforms in mouse brain.

Mammalian homologues of the Drosophila TRP proteins, which are essential for light-activated, phosphatidyl-inositide (PI)-dependent Ca2+ conductance in Drosophila photoreceptors, were molecularly identified, to investigate receptor-activated Ca2+ influx in the mammalian nervous system. Two cloned mouse TRP homologues, TRP3 and TRP4, structurally related to the voltage-dependent Na+ channel, were expressed predominantly in the brain, where a sharp contrast in the distribution of the RNA transcripts for TRP isoforms was demonstrated by in situ hybridization analysis. TRP3 mRNA was concentrated in cerebellar Purkinje cells and sparsely localized in the cerebellar granule layer, pontine nuclei, and thalamus, whereas TRP4 mRNA was abundantly expressed in hippocampal CA1 pyramidal neurons, dentate gyrus granule cells, and cerebral cortical neurons, and in the septal nuclei and the mitral layer of olfactory bulb. The distinct spatial patterns of TRP isoforms implicate that neurons are highly heterogeneous in receptor-activated Ca2+ influx responsible for the second phase of PI-mediated rise in intracellular Ca2+.

Amino Acid Sequence↗
PubMed1998

Knee and/or hip joint destruction in rheumatoid arthritis is associated with HLA-DRB1*0405 in Japanese patients.

To determine the prognostic factors for knee and/or hip joint destruction in rheumatoid arthritis (RA) patients, we typed 379 RA patients for HLA-DRB alleles and analysed the antigen frequencies. The DRB1*0405 antigen frequency in RA patients who underwent total knee replacement and/or total hip replacement was significantly higher than in those who did not have replacements, which meant that DRB1*0405 was associated with knee and/or hip joint destruction. This finding may be of value for predicting knee and/or hip joint destruction in RA.

Adolescent↗
PubMed1998

Relation between spontaneous contraction and sarcoplasmic reticulum function in cultured neonatal rat cardiac myocytes.

The relation between spontaneous contraction, Ca2+ oscillations, and sarcoplasmic reticulum (SR) function was studied in cultured neonatal rat cardiac myocytes. Spontaneous contraction and Ca2+ oscillations were irregular at day 2 of culture but became regular at day 6 of culture in neonatal rat cardiac myocytes. The rate of spontaneous contraction and the frequency of Ca2+ oscillations were decreased by verapamil and were abolished in the absence of extracellular Ca2+ at both day 2 and day 6 of culture. Ryanodine and thapsigargin increased the rate of contraction and the frequency of Ca2+ oscillations at day 2 of culture but did not affect contractions and Ca2+ oscillations at day 6 of culture. Ultrastructural observation showed that the structure of SR developed less at day 6 of culture. The present results suggest that spontaneous contraction and Ca2+ oscillations are due mainly to extracellular Ca2+ influx but not to Ca2+ release from SR in neonatal rat cardiac myocytes.

Animals↗
PubMed1998

An association between the natural course of shoulder joint destruction in rheumatoid arthritis and HLA-DRB1*0405 in Japanese patients.

To assess the association between HLA-DRB1 alleles and shoulder destruction due to rheumatoid arthritis (RA) in Japanese, we typed for HLA-DRB1 alleles in 100 Japanese RA patients who could be classified into 5 groups: non-progressive (N) with normal radiographs; erosive (E) showing marginal erosion but no collapse; collapse (C) showing subchondral cysts followed by collapse; arthrosis-like (A) showing osteoarthrotic features; and the mutilating (M) showing mutilating bone destruction. The HLA-DRB1*0405 antigen frequency in N, E, C, A, and M types was 55%, 61%, 33%, 71%, 100%, respectively. That in the M type (100%) was significantly higher than that in the others (the N, E, C, and A types; 57%). These findings suggest that the most severe shoulder joint destruction pattern in RA, the M type, is associated with HLA-DRB1*0405.

Adult↗
PubMed1998

The homozygote of HLA-DRB1*0901, not its heterozygote, is associated with rheumatoid arthritis in Japanese.

To assess the association between HLA-DRB1*0901 and Japanese rheumatoid arthritis (RA) patients, we analyzed the frequency of HLA-DRB1*0901 in 852 Japanese RA patients. We found that the homozygote of DRB1*0901 was associated with Japanese RA patients, while the heterozygote of DRB1*0901 was not. These findings suggest that DRB1*0901 is a weakly susceptible allele of RA, which in our investigation was not associated with RA by a single allele, but can be by a homozygote. DRB1*0901 does not have the shared epitope, and it is suggested that there may be some mechanism ofthe association between HLA-DRB1 and RA other than the shared epitope, which was not strong.

Alleles↗
PubMed1998

Functional characterization of ion permeation pathway in the N-type Ca2+ channel.

Multiple types of high-voltage-activated Ca2+ channels, including L-, N-, P-, Q- and R-types have been distinguished from each other mainly employing pharmacological agents that selectively block particular types of Ca2+ channels. Except for the dihydropyridine-sensitive L-type Ca2+ channels, electrophysiological characterization has yet to be conducted thoroughly enough to biophysically distinguish the remaining Ca2+ channel types. In particular, the ion permeation properties of N-type Ca2+ channels have not been clarified, although the kinetic properties of both the L- and N-type Ca2+ channels are relatively well described. To establish ion conducting properties of the N-type Ca2+ channel, we examined a homogeneous population of recombinant N-type Ca2+ channels expressed in baby hamster kidney cells, using a conventional whole cell patch-clamp technique. The recombinant N-type Ca2+ channel, composed of the alpha1B, alpha2a, and beta1a subunits, displayed high-voltage-activated Ba2+ currents elicited by a test pulse more positive than -30 mV, and were strongly blocked by the N-type channel blocker omega-conotoxin-GVIA. In the presence of 110 mM Ba2+, the unitary current showed a slope conductance of 18.2 pS, characteristic of N-type channels. Ca2+ and Sr2+ resulted in smaller ion fluxes than Ba2+, with the ratio 1.0:0. 72:0.75 of maximum conductance in current-voltage relationships of Ba2+, Ca2+, and Sr2+ currents, respectively. In mixtures of Ba2+ and Ca2+, where the Ca2+ concentration was steadily increased in place of Ba2+, with the total concentration of Ba2+ and Ca2+ held constant at 3 mM, the current amplitude went through a clear minimum when 20% of the external Ba2+ was replaced by Ca+2. This anomalous mole fraction effect suggests an ion-binding site where two or more permeant ions can sit simultaneously. By using an external solution containing 110 mM Na+ without polyvalent cations, inward Na+ currents were evoked by test potentials more positive than -50 mV. These currents were activated and inactivated in a kinetic manner similar to that of Ba2+ currents. Application of inorganic Ca2+ antagonists blocked Ba2+ currents through N-type channels in a concentration-dependent manner. The rank order of inhibition was La3+ >/= Cd2+ >> Zn2+ > Ni2+ >/= Co2+. When a short strong depolarization was applied before test pulses of moderate depolarizing potentials, relief from channel blockade by La3+ and Cd2+ and subsequent channel reblocking was observed. The measured rate (2 x 10(8) M-1 s-1) of reblocking approached the diffusion-controlled limit. These results suggest that N-type Ca2+ channels share general features of a high affinity ion-binding site with the L-type Ca2+ channel, and that this site is easily accessible from the outside of the channel pore.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1998

[Perforation of the bladder by a peritoneal catheter: an unusual late complication of ventriculo-peritoneal shunt].

Late perforation of the bladder by an abdominal catheter of a ventriculoperitoneal (VP) shunt is extremely rare. We report the successful treatment of a patient who presented with this complication. An 82-year-old woman received a V-P shunt for normal pressure hydrocephalus following subarachnoid hemorrhage. Ten years later she was admitted to our hospital with neck pain. A few days after admission, the tip of the peritoneal catheter was found to be protruding from the urethra during urination. Subsequently, the patient developed meningitis. Contrast study of the distal tubing demonstrated the continuity of the peritoneal shunt tube. After the entire system was removed, antibiotic treatment was administered for 2 weeks. and a new VP shunt was placed on the opposite side. The post-operative course was uneventful. Previous reports regarding complications after the placement of a VP-shunt show that periodic chest and abdominal X-ray studies are important. In this case, however, the peritoneal tube was not able to be observed on abdominal plain film. For this reason, an unfaded radiopaque tube is necessary if there is to be early diagnosis of late organic perforation by a peritoneal shunt tube.

Aged↗
PubMed1998

[Type A acute aortic dissection: late reoperations for dilatation of the distal false lumen and aortic regurgitation].

From January 1990 to December 1996, 71 patients aged 33 to 79 years (mean 60 +/- 11) underwent an emergency operation for type A acute aortic dissection. Fifty-three (74.6%) survived, and were followed 7 to 94 months (mean follow up 2.9 +/- 1.8 years) after the first operation. Five patients underwent reoperation for dilatation of the distal false lumen 7 to 52 months (mean period, 25 months) after primary repair. One patient underwent replacement of the arch and descending aorta, three patients underwent replacement of the descending aorta, and one patient underwent the stented graft implantation, resulting in closure of the entry site. Three patients underwent reoperation for severe aortic valve regurgitation 12 to 31 months (mean period, 24 months) after primary repair. Two patients underwent aortic valve replacement, and one patient underwent aortic root replacement. The actuarial freedom from reoperations was 81 +/- 6.9% at 3 years, and 73 +/- 9.9% at 5 years.

Adult↗
PubMed1997

Molecular cloning and characterization of a human brain ryanodine receptor.

We have cloned and sequenced the cDNA of the human brain ryanodine receptor (RyR3), which is composed of 4866 amino acids and shares characteristic structural features with the rabbit RyR3. Northern blot analysis shows that the human RyR3 mRNA is abundantly expressed in hippocampus, caudate nucleus and amygdala as well as in skeletal muscle. The human RyR3 mRNA is also detected in several cell lines derived from human brain tumors. Functional expression of RyR3 and a chimeric RyR suggests that RyR3 forms a calcium-release channel with a very low Ca2+ sensitivity.

Animals↗
PubMed1997

Relationship between specific binding of 125I-omega-conotoxin GVIA and GTP binding protein: effects of the GTP analogues, mastoparan and A1F4-.

We investigated whether the specific binding or labeling of 125I-omega-CgTX on crude membranes from chick whole brain was affected when endogenous GTP binding protein (G protein) was activated by GTP analogues, mastoparan (MP) and aluminum fluoride (AIF4-; AICl3 + NaF). Both GTPgammaS and Gpp(NH)p attenuated the inhibitory effect of selective N-type Ca channel inhibitors such as aminoglycoside antibiotics (AGs) or dynorphine (1-13)(Dyn) on specific 125I-omega-CgTX binding in a dose-dependent manner. On the other hand, the inhibitory effects of the divalent metal cations Cd2+, Co2+, Mg2+ and Mn2- on such binding were not attenuated by GTPgammaS. MP and AIF4- also attenuated the inhibitory effect of Neo on this binding similar to GTPgammaS. The attenuating effect of MP was enhanced by the presence of Mg2+ in a dose-dependent manner. However, GTP analogues, MP and AIF4-, did not affect binding or labeling without AGs or Dyn. GTPgammaS, MP and AIF4- also attenuated the specific labeling of a 215-kDa band in crude membranes with 125I-omega-CgTX using the cross-linker DSS (non-reduced condition) in the presence of Neo. These results indicate that there are direct or indirect relationships between N-type Ca channels and G proteins via binding sites for AGs or MP.

Aluminum Compounds↗