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T Oba

Publications and source records attributed to T Oba.

At least 19 recordsLinked to original sources
PubMed1995

Possible involvement of Ca(2+)-induced Ca2+ release mechanism in Ag(+)-induced contracture in frog skeletal muscle.

To determine if an Ag(+)-induced contracture is associated with the Ca(2+)-induced Ca2+ release mechanism in the sarcoplasmic reticulum, effects of Ca(2+)-induced Ca2+ release modulators on the Ag(+)-induced contracture were studied with single fibers of frog toe skeletal muscle. The fiber treated with 1 mM caffeine contracted significantly much more than controls without caffeine at Ag+ concentrations below 1 microM. Procaine shifted the Ag+ concentration-tension curve to the right, dose-dependently. When 10 mM procaine was applied to contracting fibers not treated with caffeine, the duration of 5 microM Ag(+)-induced contracture was shortened with a little decrease in tension amplitude, that was different from the effect of procaine on caffeine contracture. In caffeine solution, 0.5 microM Ag+ caused a long-lasting contracture with sometimes two peaks. 2 mM procaine led to disappearance of such two peaks, resulting in shortening of the contracture. K+ contracture was potentiated by 1 mM caffeine only at lower concentrations of K+, and inhibited by 10 mM procaine. These results suggest that the Ag(+)-induced contracture is composed of two components: Ca(2+)-induced Ca2+ release-dependent and -independent. 5 microM Ag(+)-induced contracture slowly relaxed with a wavy tension pattern to the resting level when 0.05 mM dithiothreitol was applied around peak of the tension. This relaxation was accelerated by procaine application. These findings may be explained by attributing a portion of Ag(+)-induced contracture to the effect of Ca2+ released through the Ca(2+)-induced Ca2+ release mechanism in the sarcoplasmic reticulum.

Animals↗
PubMed1995

DNase I interaction on muscle Z-line.

The effect of deoxyribonuclease I on muscle Z-line structures was re-examined. Under conditions of deoxyribonuclease I activation (presence of the divalent cation Ca2+ and Mg2+), a deoxyribonuclease I preparation did not affect Z-line structure if phenylmethylsulfonylfluoride, an inhibitor of serine proteases, was also present. In the absence of protease inhibitor, both Z-lines and M-lines were digested, even in the presence of EDTA and EGTA as inhibitors of deoxyribonuclease I. These electron microscopic observations were consistent with the following results from sodium dodecyl sulphate gel electrophoresis: when the protease was inhibited but deoxyribonuclease I was activated, myofibrillar proteins remained essentially intact. However, degradation of proteins in both rabbit psoas and chicken pectoralis myofibrils was observed in the presence of deoxyribonuclease I inhibitors when the protease inhibitor was absent. Our data strongly suggest that the interaction of deoxyribonuclease I with Z-line proteins previously reported is most likely due to contamination of the deoxyribonuclease I fraction by the serine-type proteases.

Animals↗
PubMed1994

Overproduction and purification of Lon protease from Escherichia coli using a maltose-binding protein fusion system.

Lon protease, which plays a major role in degradation of abnormal proteins in Escherichia coli, was overproduced and efficiently purified using the maltose-binding protein (MBP) fusion vector. The MBP-Lon fusion protein was expressed in a soluble form in E. coli and purified to homogeneity by amylose resin in a single step. Lon protease was split from MBP by cleaving a fusion point between MBP and Lon with factor Xa and purified by amylose resin and subsequent gel filtration. In this simple method, Lon protease was purified to homogeneity. Purified MBP-Lon fusion protein and Lon protease showed similar breakdown activities with a peptide (succinyl-L-phenylalanyl-L-leucyl-phenylalanyl-beta-D-methoxynaphthyl amide) and protein (alpha-casein) in the presence of ATP. Therefore, the gene-fusion approach described in this study is useful for the production of functional Lon protease. MBP-Lon fusion protein, which both binds to the amylose resin and has ATP-dependent protease activity, should be especially valuable for its application in the degradation of abnormal proteins by immobilized enzymes.

2-Naphthylamine↗
PubMed1992

Ag(+)-induced inward current on frog skeletal muscle.

Ag+ caused an inward current on voltage-clamped skeletal muscle. The current was carried by Ca2+, Mg2+, and Na+, and was blocked by Cd2+ or Ni2+ but not by nifedipine or D600. Channel gating is supposed to be modified by Ag+.

Animals↗
PubMed1992

Silver-induced frog skeletal muscle contraction and its modulation by calcium antagonists nifedipine and felodipine and calcium agonist Bay K 8644.

1. Ag+ induces one phase of a transient contracture in frog skeletal muscle (0.3-10 microM) and potentiates twitch tension when the fiber is given continuous stimulation. 2. The potentiation of fiber contraction by Ag+ is similar to the effect of Ca2+ antagonists nifedipine and felodipine. 3. Bay K 8644 (100 nM) potentiates and accelerates Ag(+)-induced tension development and the inactivation occurs more rapidly than in the control (Ag+ alone). 4. Two factors can be considered to be essential for the induction of Ag+ contracture: (1) a certain number of Ag+ ions must bind to free SH groups of the voltage sensor; and (2) the binding must occur within a limited time to raise the mechanical threshold to induce contracture. 5. All results suggest that Ag+ binding to crucial SH groups on the Ca2+ channel may be responsible for the activation of muscle contraction, potentiation, and the inhibition of excitation-contraction coupling in skeletal muscle.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1992

Modulation of the Ca2+ channel voltage sensor and excitation-contraction coupling by silver.

Ag+ (0.5-10 microM) is known to produce a transient contraction of intact frog skeletal muscle fibers followed by complete inhibition of excitation-contraction (E-C) coupling. We have carried out physiological and biochemical experiments to investigate the basis of this effect. Dihydropyridine (DHP) Ca2+ channel blockers, which inhibit the voltage sensor of the Ca2+ channel, completely inhibit Ag+ contractions. Removal of extracellular Ca2+, or blockade of Ca2+ entry with cadmium, does not inhibit Ag+ contractions. Activation of the Ca2+ channel's voltage sensor with the Ca2+ channel agonists Bay K 8644 or with perchlorate, potentiates the Ag(+)-induced contraction. Ag+ binds to the partially purified rabbit skeletal muscle Ca2+ channel and inhibits DHP binding (IC50 = 1.1 microM) and sulfhydryl (SH) reactivity (IC50 = 0.11 microM) over the concentration range where it inhibits E-C coupling. Oxidation of free SH groups by H2O2 or their reaction with DTNB prevents Ag+ contractions, while DTT reduction of oxidized SH groups restores Ag+ contractions. These results suggest that Ag+ binds to critical SH groups on the DHP receptor Ca2+ channel, resulting in modification of the channel's voltage sensor and the failure of E-C coupling.

Animals↗
PubMed1992

Partial inhibition of skeletal muscle contraction by dantrolene sodium and its modification with perchlorate and Bay K 8644.

The effects of dantrolene sodium (DAN) on the dihydropyridine receptor (DHPR) of the transverse (T) tubule voltage sensor (Ca2+ channel) was studied with single fibers from bullfrog toe muscle. Perchlorate (ClO4-), which acts selectively on the DHPR, overcame DAN-induced inhibition of twitch tension. Bay K 8644, a DHPR agonist, slowed the rate of twitch inhibition by DAN. DAN inhibited twitch tension to a greater extent in Ca(2+)-free solution than in Ringer solution or solution containing Zn2+, whereas twitch inhibition by DAN was less in caffeine-containing solution than in the control. The effects of DAN on Zn(2+)- and caffeine-treated fibers and on fibers in Ca(2+)-free solution suggest that DAN must act near the voltage sensor of the T tubule. However, differences in net twitch inhibition by DAN between control fibers and fibers potentiated by ClO4- or Bay K 8644 suggest that DAN does not bind to the same site as these potentiating agents do. The role of myoplasmic Ca2+ in DAN-induced inhibition of twitch and the effects of DAN on the mechanical threshold and membrane potential in skeletal muscle are discussed.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

CGG: an unassigned or nonsense codon in Mycoplasma capricolum.

CGG is an arginine codon in the universal genetic code. We previously reported that in Mycoplasma capricolum, a relative of Gram-positive eubacteria, codon CGG did not appear in coding frames, including termination sites, and tRNA(ArgCCG) pairing with codon CGG, was not detected. These facts suggest that CGG is a nonsense (unassigned and untranslatable) codon--i.e., not assigned to arginine or to any other amino acid. We have investigated whether CGG is really an unassigned codon by using a cell-free translation system prepared from M. capricolum. Translation of synthetic mRNA containing in-frame CGG codons does not result in "read-through" to codons beyond the CGG codons--i.e., translation ceases just before CGG. Sucrose-gradient centrifugation profiles of the reaction mixture have shown that the bulk of peptide that has been synthesized is attached to 70S ribosomes and is released upon further incubation with puromycin. The result suggests that the peptide is in the P site of ribosome in the form of peptidyl-tRNA, leaving the A site empty. When in-frame CGG codons are replaced by UAA codons in mRNA, no read-through occurs beyond UAA, just as in the case of CGG. However, the synthesized peptide is released from 70S ribosomes, presumably by release factor 1. These data suggest strongly that CGG is an unassigned codon and differs from UAA in that CGG is not used for termination.

Amino Acid Sequence↗
PubMed1990

Analysis of MRI and SPECT in patients with acute head injury.

Traumatic lesions defined by magnetic resonance (MR) imaging were divided into two groups according to findings on computed tomography (CT). This classification reflected difference in the regional cerebral blood flow (rCBF). In the contusional lesions which CT could demonstrate, rCBF varied from hyperperfusion to hypoperfusion, while it was almost always decreased in the lesions which CT could not detect. These results suggest that the former may include a mixture of brain oedema and hyperemia and the latter may imply brain oedema. MR imaging can reveal the minor oedema which CT fails to show in patients with acute head injury.

Acute Disease↗
PubMed1990

Sulfhydryls on frog skeletal muscle membrane participate in contraction.

To examine the molecular mechanism underlying contractile activation, we studied effects of a sulfhydryl reagent, N-(7-dimethylamino-4-methylcoumarinyl)maleimide (DACM), on twitch, Ag(+)-induced contraction, and K+ and caffeine contractures in single toe muscle fibers of frog. DACM suppressed twitch and Ag(+)-induced contraction, dose dependently, but not caffeine contracture. K+ contracture also was decreased appreciably by exposure to 40 microM DACM for 10 min. DACM elicited no shift of the mechanical threshold or inhibition of resting potential but slightly inhibited action potential. Increase of the fluorescence intensity produced by binding of 10 microM DACM to sulfhydryl groups was depressed by brief pretreatment with 100 microM Ag+. When exposed to 1 mM dithiothreitol (DTT) within 5 s of the rising phase of 5 microM Ag(+)-induced contraction, the fiber rapidly decreased the tension to the resting level. In this case, reapplication of 5 microM Ag+ after washing out DTT elicited a new contraction similar to the first Ag(+)-induced contraction. The second contraction amplitude depended on the time between the onset of the first Ag(+)-induced contraction and DTT application. If DTT was applied after more than 16 s, tension no longer developed on the second exposure to Ag+ or K+. The experiments provide evidence that crucial sulfhydryl groups participate in muscle activation. The possible role of the sulfhydryl group on the transverse tubular membrane in tension development is discussed.

Animals↗
PubMed1990

Effects of tetraphenylboron-induced increase in inner surface charge on Ca2+ release from sarcoplasmic reticulum.

We studied the relationship between surface charge and release of Ca2+ in the heavy sarcoplasmic reticulum (SR) of skeletal muscle. The inner and outer surface potentials and charge densities of the membrane treated with a lipophilic anion, tetraphenylboron (TPB-), were measured using 1-anilino-8-naphthalene-sulfonate fluorescence. Ca2+ was loaded passively or actively by the SR. Ca2+ release was estimated by the fluorescence of chlortetracycline, and protein conformational change was monitored by use of the sulfhydryl group fluorescent probe, N-(7-dimethylamino-4-methyl-3-coumarinyl) maleimide (DACM). Treatment of Ca2(+)-loaded SR vesicles with micromolar TPB- dose-dependently increased the local fixed negative charge on the inner surface, and changed the DACM fluorescence intensity in parallel with the Ca2+ release. The changes in surface charge and in DACM fluorescence intensity did not originate from the Ca2+ flux. A lipophilic cation, tetraphenylarsonium (TPA+), screened the negative inner surface charge which was increased by TPB-, and inhibited both TPB(-)-induced change in DACM fluorescence intensity and Ca2+ release. Millimolar Mg2+ reduced degrees of TPB(-)-induced Ca2+ release from the SR and of TPB(-)-induced contraction in mechanically skinned fibers. Mg2+ did not inhibit the increase in the negative inner surface charge and DACM fluorescence intensity produced by TPB-. Thus, the local increase in negative charge on the SR inner membrane leaflet seems to be causally related to the Ca2+ release. Mg2+ and TPA+ are suggested to inhibit TPB(-)-induced Ca2+ release by different mechanisms.

Animals↗
PubMed1990

[MR imaging of traumatic cerebellar dysfunction].

Four cases of cerebellar dysfunction following head trauma are presented. Cerebellar signs revealed were those such as dysmetria, dysdiadochokinesis, horizontal nystagmus and ataxia. T2-weighted magnetic resonance (MR) imaging (0.15 tesla, spin-echo method; TR 2000 msec. and TE 100 msec.) revealed focal lesions in these patients, although CT scan failed to demonstrate any changes in the cerebellum. The cerebellar symptoms were maximal immediately after the trauma but improved gradually in two cases. These are compatible with the transient traumatic cerebellar dysfunction postulated by R. C. Cantu in 1969. The pathophysiology of this syndrome, whether it is due to cerebellar concussion or contusion, has not yet been determined. The abnormality of the cerebellum revealed by MR imaging seemed to be contusion rather than concussion. Therefore the authors presume that transient traumatic cerebellar dysfunction is caused by minor cerebellar contusion. In the other two cases, delayed epidural hemorrhage ensued and the symptoms disappeared rapidly after evacuation of the hematoma. In these patients, occurrence of delayed epidural hematoma in the posterior cranial fossa was predicted by MR imaging. The authors regard the lesion as an alarm signal indicating the probable occurrence of infratentorial hematoma.

Adult↗
PubMed1989

Calcium release from frog sarcoplasmic reticulum by an imidazolyl reagent.

Calcium is released from the isolated heavy sarcoplasmic reticulum (SR) of frog skeletal muscle upon application of 0.1-1 mM diethylpyrocarbonate (DEP, an imidazolyl reagent). The Ca-ATPase activity of SR was suppressed by 20% in the presence of 1 mM DEP. More than 1 mM of free magnesium ion or 5 microM ruthenium red eliminated the effect of DEP on calcium release but not on Ca-ATPase activity. A plausible site of DEP action is on the calcium channel.

Animals↗
PubMed1989

Caffeine treatment inhibits drug-induced calcium release from sarcoplasmic reticulum and caffeine contracture but not tetanus in frog skeletal muscle.

Effects of pretreatment with caffeine on Ca2+ release induced by caffeine, thymol, quercetin, or p-chloromercuriphenylsulfonic acid (pCMPS) from the heavy fraction of sarcoplasmic reticulum (SR) were studied and compared with those effects on caffeine contracture and tetanus tension in single fibers of frog skeletal muscle. Caffeine (1-5 mM) did induce transient Ca2+ release from SR vesicles, but subsequent further addition of caffeine (10 mM, final concentration) induced little Ca2+ release. Ca2+ release induced by thymol, quercetin, or pCMPS was also inhibited by pretreatment with caffeine. In single muscle fibers, pretreatment with caffeine (1-5 mM) partially reduced the contracture induced by 10 mM caffeine. However, tetanus tension was almost maximally induced by electrical stimulus in caffeine-treated fibers. These results indicate that SR, which becomes less sensitive to caffeine, thymol, quercetin, or pCMPS by pretreatment with caffeine, can still respond to a physiological signal transmitted from transverse tubules.

4-Chloromercuribenzenesulfonate↗
PubMed1989

Ruthenium red and magnesium ion partially inhibit silver ion-induced release of calcium from sarcoplasmic reticulum of frog skeletal muscles.

Effects of Ca2+-induced Ca2+ release blockers, ruthenium red (RR) and Mg2+, on Ag+-induced Ca2+ release were studied using skinned muscle fibers or fragmented heavy SR (HSR) prepared from frog muscle, and compared with those on caffeine-induced one. Exposure of the skinned fibers to 5 microM Ag+ produced a rapid and large contraction in the presence of 0.043 mM free Mg2+. When Mg2+ concentration was increased to 0.86 mM, Ag+ led to a large transient contraction, combined with a small tonic one. The transient component was completely blocked by high Mg2+ (3.64 mM), but the tonic one was not. Ca2+-ATPase activity was not stimulated by increase of Mg2+ from 0.86 to 3.64 mM. Ag+ and caffeine induced a rapid Ca2+ efflux from HSR in a dose-dependent manner. RR over a range from 1 to 10 microM dose-dependently inhibited the Ca2+ efflux induced by 10 microM Ag+. Despite increase of RR to 30 microM, however, further inhibition of the Ca2+ efflux was not produced any more (77.8 +/- 12.2% inhibition). A 10 mM caffeine-induced efflux of Ca2+ was blocked slightly by only 0.5 microM RR and almost completely by 3 microM. A slight inhibition (about 28%) of the Ca2+-ATPase activity was observed in the presence of 10 microM Ag+ in 0.5 mg SR protein/ml of medium. RR and caffeine did not affect the enzyme activity. These results indicate that frog SR could induce a rapid release of Ca2+ upon Ag+ and caffeine, suggesting that Ag+ may have two different binding sites to release Ca2+; one is on Ca2+-induced Ca2+ release channel and the other on RR-insensitive site.

Animals↗