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Biomedical subjects

A Takai

Publications and source records attributed to A Takai.

At least 55 records · Page 3Linked to original sources
PubMed1989

Protein phosphatase composition in the smooth muscle of guinea-pig ileum studied with okadaic acid and inhibitor 2.

Using okadaic acid, a potent inhibitor of type 2A and type 1 protein phosphatases, and inhibitor 2, an intrinsic inhibitory factor of type 1 phosphatase, we characterized the phosphorylated myosin light-chain (PMLC) phosphatase activity in the smooth-muscle extracts of guinea-pig ileum. In the intact fibres the control activity was 254 +/- 13 nmol of Pi/min per g wet wt. (n = 15) against 32P-labelled PMLC (4 microM) from chicken gizzard. The following phosphatase fractions were identified: an inhibitor-2-sensitive (type 1) fraction (fractional activity = 35%), a Mg2+-dependent and okadaic acid-insensitive (type 2C) fraction (17%), and two type 2A-like fractions that had different susceptibility to okadaic acid. The type 2A-like fraction with lower affinity to okadaic acid accounted for 30% of the control activity. After the cell membrane was permeabilized by Triton X-100, more than 60% of this fraction remained and accounted for about 90% of the total activity, whereas the other fractions were nearly abolished. The type 2A-like fraction may be bound to some intracellular structure such as contractile proteins.

Animals↗
PubMed1989

Polypoid squamous cell carcinoma of the esophagus.

Since 1971, 111 patients with esophageal carcinoma have undergone esophagectomy at the affiliated hospitals of Nippon Medical School. Of the 101 patients with ordinary squamous cell carcinoma, seven (7%) had intraluminal polypoid masses, endoscopically, and radiologically. The criteria used to select cases were as follows: (1) a size greater than 3 cm, (2) an intraluminal polypoid or pedunclated tumor, and (3) absence of wall construction and ulceration. Four of the seven polypoid cases have survived more than 5 years. One has lived more than 3 years. The 5-year survival rate of those patients with the polypoid type was 71%, but it was only 11% for the other types (P less than 0.05). Age, sex, size or location of the tumor, histologic grade, or lymph node metastasis did not affect survival. Only the incidence of adventitial involvement was significantly lower for the polypoid type. These results indicate that polypoid-type squamous cell carcinoma of the esophagus has a fairly good prognosis after surgery.

Aged↗
PubMed1989

Okadaic acid, a phosphatase inhibitor, produces a Ca2+ and calmodulin-independent contraction of smooth muscle.

The effects of okadaic acid, a phosphoprotein phosphatase inhibitor, on the contractile response and on myosin light chain phosphorylation were studied in intact lamb tracheal smooth muscle. The effects of okadaic acid were compared to the response of the same fibers stimulated with 1 microM methacholine, a concentration that induces 90% of maximal force. Okadaic acid (50 microM) produced a slow but maximal contraction that was accompanied by an increase in phosphorylation of the 20 kDa light chain of myosin. The myosin light chain phosphorylation pattern induced by okadaic acid, however, differed from that induced by methacholine. Ca2+ depletion, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), a calmodulin antagonist and 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), a protein kinase C inhibitor, blocked or attenuated methacholine-induced contractions but had no significant effect on force development or myosin light chain phosphorylation induced by okadaic acid. These results suggest that phosphorylation of the 20 kDa light chain of myosin is essential for smooth muscle contraction; they also suggest that okadaic acid either uncovers or activates an apparently Ca2+ and calmodulin-independent protein kinase activity that phosphorylates the 20 kDa light chain of myosin at multiple sites.

Animals↗
PubMed1988

Inhibitory effect of a marine-sponge toxin, okadaic acid, on protein phosphatases. Specificity and kinetics.

The inhibitory effect of a marine-sponge toxin, okadaic acid, was examined on type 1, type 2A, type 2B and type 2C protein phosphatases as well as on a polycation-modulated (PCM) phosphatase. Of the protein phosphatases examined, the catalytic subunit of type 2A phosphatase from rabbit skeletal muscle was most potently inhibited. For the phosphorylated myosin light-chain (PMLC) phosphatase activity of the enzyme, the concentration of okadaic acid required to obtain 50% inhibition (ID50) was about 1 nM. The PMLC phosphatase activities of type 1 and PCM phosphatase were also strongly inhibited (ID50 0.1-0.5 microM). The PMCL phosphatase activity of type 2B phosphatase (calcineurin) was inhibited to a lesser extent (ID50 4-5 microM). Similar results were obtained for the phosphorylase a phosphatase activity of type 1 and PCM phosphatases and for the p-nitrophenyl phosphate phosphatase activity of calcineurin. The following phosphatases were not affected by up to 10 microM-okadaic acid: type 2C phosphatase, phosphotyrosyl phosphatase, inositol 1,4,5-trisphosphate phosphatase, acid phosphatases and alkaline phosphatases. Thus okadaic acid had a relatively high specificity for type 2A, type 1 and PCM phosphatases. Kinetic studies showed that okadaic acid acts as a non-competitive or mixed inhibitor on the okadaic acid-sensitive enzymes.

Animals↗
PubMed1988

Effects of a protein phosphatase inhibitor, okadaic acid, on membrane currents of isolated guinea-pig cardiac myocytes.

The effects of a protein phosphatase inhibitor, okadaic acid (OA), were studied on membrane currents of isolated myocytes from guinea-pig cardiac ventricle. The whole-cell Ca2+ current (ICa) was recorded as peak inward current in response to test pulse to 0 mV. Extracellular application of OA (5-100 microM) produced an increase of ICa. The effect was markedly enhanced when the myocyte was pretreated with threshold concentrations of isoprenaline. ICa was increased from 11.3 +/- 0.8 microA cm-2 to 19.0 +/- 1.1 microA cm-2 (n = 4) by 5 microM-OA in the presence of 1 nM-isoprenaline. The delayed rectifier current was also slightly increased. Furthermore, the wash-out time of the beta-adrenergic increase of ICa was markedly prolonged by OA. The beta-adrenergic stimulation of cardiac Ca2+ current is thought to be mediated by cAMP-dependent phosphorylation. The present results strongly suggest that the effect of OA on ICa is related to inhibition of endogenous protein phosphatase activity which is responsible for the dephosphorylation process. By the isotope method, the inhibitory effect of OA on different types of phosphatase was compared. OA had a relatively high specificity to type 1-, and type 2A-phosphatases.

Animals↗
PubMed1988

Okadaic acid. Protein phosphatase inhibition and muscle contractile effects.

Okadaic acid (OA;C44H66O13) is a polyether derivative of a C38 fatty acid first isolated from marine sponges of the genus Halichondria . It is thought to be synthesized by marine diflagellates and to accumulate in the other marine organisms such as sponges and shellfishes which feed on them. Physiologically, OA has been known to have a marked contractile effect on smooth muscles and heart muscle. Recent results strongly suggest that these contractile effects are due to the inhibitory action of OA on the intracellular protein phosphatase activity.

Animals↗
PubMed1988

Effects of okadaic acid on isometric tension and myosin phosphorylation of chemically skinned guinea-pig taenia coli.

1. In guinea-pig taenia coli skinned with Triton X-100, the marine sponge toxin okadaic acid (OA; 0.1-10 microM) produced a dose-dependent enhancement of isometric tension in the presence of low concentrations (0.1-1 microM) of Ca2+. 2. The Ca2+-tension relation of the skinned taenia showed a high co-operativity (Hill coefficient, h = 5) in the presence of 0.2 microM-calmodulin. The concentration of Ca2+ required to obtain half-maximal tension (ED50) was 1.8 microM. OA (5 microM) reduced the co-operativity (h = 2.3) and increased the Ca2+ sensitivity (ED50 = 0.92 microM-Ca2+). OA further increased the tension produced with 30 microM-Ca2+, while it failed to produce any mechanical effect in Ca2+-free solution. When the calmodulin concentration was increased the Ca2+ sensitivity increased as well, but the co-operativity was not affected both in the absence and in the presence of OA. 3. The level of myosin phosphorylation was analysed by two-dimensional gel electrophoresis. OA produced an increase in phosphorylated light chains and a concomitant decrease in unphosphorylated light chains. The effect was completely reversed when OA was washed out. 4. In solutions containing more than 1 microM-Ca2+, a third protein band appeared on the gels next to the bands of light chains. OA markedly increased the third band which disappeared when OA and Ca2+ were simultaneously removed. 5. OA reversibly slowed down both relaxation and dephosphorylation induced by Ca2+ removal following activation with 30 microM-Ca2+. Complete relaxation did not occur in the presence of more than 1 microM-OA. The concentration of OA required to produce a 50% reduction (ID50) of the relaxation rate was 78 nM. 6. The phosphatase activity in the taenia extract was inhibited by OA (1-10 microM) in a dose-dependent manner. The inhibition was well described as a mixed noncompetitive inhibition, and the dose-inhibition relation was shifted to the right when the concentration of substrate (phosphorylated light chains) was increased. The lower and upper limits of the change of ID50 produced by changing the substrate concentration were estimated to be 10 and 165 nM-OA, respectively. 7. These results strongly suggest that the tension enhancement and the slow-down of relaxation are both causally related to inhibition of myosin phosphatase activity by OA.

Animals↗
PubMed1988

Phosphorous compounds studied by 31P nuclear magnetic resonance spectroscopy in the taenia of guinea-pig caecum.

1. In the isolated taenia (0.4-0.6 g) of guinea-pig caecum, the intracellular phosphorous compounds and pH were investigated using 31P nuclear magnetic resonance (NMR) under various metabolic conditions. 2. The ratios of the intracellular concentration of phosphocreatine ([ PCr]) and inorganic phosphate [( Pi]) to nucleotide triphosphate ([ NTP]) were 1.71 +/- 0.14 and 0.58 +/- 0.11 (n = 25), respectively, in normal solution (32 degrees C). The intracellular pH estimated from the chemical shift of Pi was 7.05 +/- 0.06 (n = 25), agreeing well with those previously obtained. 3. In the absence of glucose, the [PCr] and [NTP] were decreased to almost a half after 150 min exposure to 40 mM-K+ solution, while [Pi] was increased 3-fold. These changes were much faster than the rate of decline in tension. When glucose was readmitted, the contractile response to K+ fully recovered in 50 min. However, this was accompanied with only a partial recovery of [PCr] and [Pi], but no recovery of [NTP]. The intracellular pH was lowered by about 0.2 of a unit, suggesting an increase in glycolysis. 4. In Ca2+-free solution, respiratory inhibition with hypoxia or CN (1 mM) only decreased [PCr], leaving [NTP] nearly unchanged. On the other hand, respiratory inhibition in excess-K+ solution containing Ca2+ (2.4 mM) severely depleted PCr and decreased [NTP] to 40%. Increasing glucose to 50 mM did not prevent these changes, although it increased tension development. 5. The simultaneous decrease of [NTP] and [PCr] during K+ contracture suggests that the activity of creatine phosphokinase is low. The recovery from respiratory inhibition was much better for [PCr] than for [NTP]. Slow, but perfect, recovery of all NTP peaks was produced by adding 1 mM-adenosine to normal solution. 6. It was suggested that tension development is closely related to the turnover rate of ATP, and not to its concentration, and that deamination of adenosine is a limiting factor in the recovery of ATP after excessive consumption.

Adenosine↗
PubMed1987

Smooth muscle myosin phosphatase inhibition and force enhancement by black sponge toxin.

Smooth muscle contraction depends on the state of myosin phosphorylation and hence on the balance of myosin light chain kinase and phosphatase activity. Effects of okadaic acid isolated from black sponge on both enzyme activities and contractility were studied in chemically skinned fibers from guinea pig taenia coli. The toxin strongly inhibits myosin phosphatase and enhances tension development.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1987

Intraductal spread of esophageal squamous cell carcinoma.

In order to determine the pathways of tumor dissemination in esophageal carcinoma, 175 lesions of squamous cell carcinoma of the esophagus were studied histopathologically and by electron microscope in relation to the intraepithelial spread and involvement of the esophageal glands by the carcinoma. The study compared vessel invasion and lymph node metastasis. Intraepithelial spread was seen in 111 lesions (63%) and gland duct involvement in 33 lesions (19%). Gland duct involvement was observed in 30% of the lesions positive for intraepithelial spread. In the intramucosal carcinomas, gland duct involvement was observed in 24%. Even in a very small carcinoma 7 X 5 mm in size, ductal spread was detected. This carcinoma did not reach the submucosa through stromal invasion. Patients with intramucosal carcinoma showed low incidence (20%) of lymphatic and/or blood vessel invasion and no incidence of lymph node metastasis. Examination by electron microscope showed that the cancer cells of the intraepithelial spread entered the duct by raising the normal ductal epithelium in the ductal cavity although the basal lamina was retained. Normal gland duct cells and cancer cells were either attached with desmosomes directly or were separated by degenerated epithelial cells. A high incidence of ductal involvement of the esophageal glands was seen in squamous cell carcinoma of the esophagus, indicating its possible importance as a route to the deep tissue in the early stage of this carcinoma.

Adult↗
PubMed1987

Carcinoma with signet ring cells of the esophagus.

A 55-year-old man with carcinoma with signet ring cells of the esophagus is described. The results of morphological examination are presented, and the classification and histogenesis of this rare tumor are discussed. Morphological examinations revealed this tumor to be composed of squamous, mucous-positive and signet ring cells. The signet ring cell had an intracytoplastic microcyst and bundles of tonofilaments. These findings suggested that the signet ring cell was an intermediate form of squamous and adenocarcinoma cells. The findings for these three components indicated that the tumor was a kind of mucoepidermoid carcinoma. Histological findings suggested this tumor's development originated from the esophageal mucosal epithelium.

Adenocarcinoma, Mucinous↗
PubMed1986

Glycolysis and oxidative phosphorylation during activation of the sodium pump in the taenia from guinea-pig caecum.

1. In the taenia from the guinea-pig caecum, the relative contribution of glycolysis and oxidative phosphorylation to activation of the Na pump was estimated by measuring changes in the rate of O2 consumption (QO2) and lactate production (Q1act). The Na pump was activated by K readmission following prior treatment with K-free solution. The QO2 and Q1act were both increased significantly by K readmission 60 min after exposure to K-free solution. These changes and the reaccumulation of tissue K were abolished by ouabain (10 microM). Spontaneous mechanical activity ceased in K-free solution and the K-induced increase in QO2 and Q1act was produced before the mechanical activity was restarted. 2. Similar changes were obtained when ouabain (10 microM) was removed after 60 min treatment. It was estimated from the changes in QO2 and Q1act that the oxidative and glycolytic metabolism each supplied about 50% of the total ATP demand for pump activation. 3. In Ca-free solution, the increase in QO2 caused by K readmission was transient and QO2 returned to the previous value in K-free solution in 10-20 min. However, the increase in QO2 was maintained in the absence of glucose. When glucose was replaced with beta-hydroxybutyrate (beta-HB, 11.8 mM), which is metabolized only through oxidative phosphorylation, K readmission also produced a sustained increase in QO2. 4. In glycogen-depleted preparations, K readmission produced little or no increase in QO2 in the absence of substrate or in the presence of glucose. On the other hand, in the presence of beta-HB (11.8 mM), a typical increase in QO2 (about 0.1 mumol min-1 g-1) was observed in response to K readmission. Lactate production was negligible in the absence of substrate or in the presence of beta-HB, but it was significantly increased after K readmission in the presence of glucose. The increase in tissue K content following K readmission was the same in the presence of glucose or beta-HB. 5. In the glycogen-depleted preparations the increase in QO2 caused by beta-HB was dependent on the presence of both Na and K in the medium, and sensitive to ouabain. Furthermore, this response was reversibly suppressed by glucose.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Possibility of metabolic control of membrane excitation.

In the guinea pig taenia coli, when glycogen is depleted by repeating Ca-induced contracture in excess K solution containing no glucose, the tension cannot be maintained. The decrease in tension is accompanied by reduction of high energy phosphate compounds and oxygen consumption. When substrate is readmitted to the glycogen-depleted preparation in the presence of 2.4 mM Ca and 20 mM K, the first response is hyperpolarization of the membrane and relaxation, and this is followed by depolarization and development of contracture. The latter response is blocked by verapamil, suggesting that energy supply increases the Ca conductance of the plasma membrane. The early response is considered to be due to activation of electrogenic Ca pump, since this is not affected by ouabain as well as removal of Na and K. ATP produced by substrate readmission is probably preferentially utilized for Ca pump activation to reduce the intracellular Ca. The recovery of tension is likely to be brought about by ATP supply not only to the contractile machinery but also to the plasma membrane to remove inactivation of Ca conductance. It is postulated that as the energy source is depleted, energy consumption is automatically limited by suppressing Ca influx, as a self-defence mechanism. Since beta HB is as effective as glucose in the recovery of these processes, and also in the activation of electrogenic Na pump, the metabolic pathway of oxidative phosphorylation alone can support these functions without a contribution of the glycolytic pathway.

Animals↗
PubMed1985

Polyclonal B cell activation during the course of Angiostrongylus cantonensis infection.

The numbers of IgM antibody forming cells against various heterologous antigens: SRBC, HRBC, TNP and FITC, were found to be elevated in the spleens of rats after infection with Angiostrongylus cantonensis. In these rats, the number of splenic B cells and total IgG and IgM levels in serum also increased spontaneously about 2- to 3-fold of uninfected rats during the course of the infection. These results suggested that A. cantonensis infection may activate B cells polyclonally in the spleens of the infected rats. While, it was clearly observed that the antibody response to SRBC injection was significantly depressed in these rats, compared to those of uninfected rats. The relation between the polyclonal B cell activation and the immunodepression was discussed.

Angiostrongylus↗