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H Ebata

Publications and source records attributed to H Ebata.

At least 19 recordsLinked to original sources
PubMed1992

Enhanced spontaneous calcium efflux and decrease of calcium-dependent calcium release from the isolated perfused heart of spontaneously hypertensive rats.

OBJECTIVE: The aim of this study was to clarify the further details of calcium handling in hypertension. DESIGN: By preserving the physiological environment of cell membrane, whole hearts were used for comparison of calcium flux between spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. METHODS: Hearts from SHR and WKY rats were perfused with Krebs-Henseleit solution under constant flow and the effluent collected. RESULTS: After labelling of the heart with 45Ca2+ (100 mumol/l), 45Ca2+ binding was found to be saturated, and washing with calcium-free perfusion solution showed two exponential curves for calcium dissociation, indicating a fast (alpha-) and slow (beta-) phase. The half-lives of the beta-phase for both 4- and 8-week-old SHR were significantly shorter than those for age-matched WKY. Also in this phase, infusion of non-radioactive Ca2+ caused a transient dose-dependent release of 45Ca2+. A significant reduction in the amount of 45Ca2+ release induced by 2 mmol/l Ca2+ was observed in both 4- and 8-week-old SHR compared with age-matched WKY rats. Infusion of lanthanum, caffeine, ionomycin (calcium ionophore) and treatment of the hearts with ethyleneglycol-bis-(beta-aminoethylether)-N,N,N,',N'-tetraac etic acid did not alter 45Ca2+ release by non-radioactive Ca2+. From these observations, 45Ca2+ is presumably released from the intracellular calcium pool, and not from extracellular binding sites or sarcoplasmic reticulum. CONCLUSIONS: These findings suggest that an abnormal calcium-handling defect (enhanced calcium efflux and reduction of membrane-bound Ca2+) exists under physiological conditions before and after the onset of hypertension, and that this may be a primary characteristic of SHR.

Aging↗
PubMed1992

[A study of progression in hepatocarcinogenesis using cell transplantation system].

It is important to distinguish a precancerous lesion and hepatocellular carcinoma (HCC) with diploidy or aneuploidy nuclear DNA pattern, not only in clinical cases but also in experimental carcinogenesis models. Using liver perfusion technique, we detected early HCC from persistent hyperplastic nodules (HN) which were induced in Wistar rats by intermittent 5-6 months administration of 2-acetylaminofluorene. This investigation was undertaken to assess both promotive and progressive effects of liver regeneration following partial hepatectomy (PH). Results are as follows: 1) Isolated hepatocytes of precancerous HN, which were transplanted into the spleen, didn't develop to HCC by 2 months after 70% PH of host liver. 2) Diced tissues of HCC, which were transplanted into the liver via portal vein, grew many metastasis in 10/10 by 7 weeks after PH, while 5/19 in control. 3) Nuclear DNA patterns of early HN-late HCC in rat liver were diploidy at the rate of more than 90% each. But it changed to aneuploidy, when inoculation of HCC for one month was repeated 7 times in the spleen.

Animals↗
PubMed1991

Reduced calcium sensitivity of dihydropyridine binding to calcium channels in spontaneously hypertensive rats.

To explore the role of calcium channels in hypertension, dihydropyridine ([3H]PN200-110) binding to heart, brain, and skeletal muscle microsomes of 4-, 8- and 15-week-old spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats was measured. At a constant Ca2+ ion concentration (pCa 3.0), maximal binding (Bmax) of dihydropyridine binding to heart and brain microsomes was significantly enhanced in 8- and 15-week-old SHR compared with WKY rats (p less than 0.01), whereas this phenomenon was not observed in 4-week-old SHR and WKY rats. Bmax and dissociation constant (Kd) values for skeletal muscle microsomes from SHR showed no difference compared with WKY rats irrespective of age. Dihydropyridine binding to heart microsomes, brain microsomes, and solubilized skeletal muscle microsomes exhibited strong calcium dependence. The Ca2(+)-dependent dihydropyridine binding curves for heart showed a Hill slope, and pK 0.5 values for 15-week-old SHR and WKY rats were 0.70 +/- 0.12 and 4.66 +/- 0.12 versus 0.72 +/- 0.12 and 5.66 +/- 0.08 (n = 4, mean +/- SD), respectively, indicating that 15-week-old SHR require 10-fold higher calcium concentration than WKY rats to promote dihydropyridine binding. The pK 0.5 values of calcium for brain and solubilized skeletal muscle calcium channels in 15-week-old SHR were also significantly lower than in WKY rats. This difference first became apparent in SHR and WKY rats as early as 4 and 8 weeks after birth. These results suggest that enhancement of calcium channel density might occur in the heart and brain of SHR in response to elevated blood pressure and that reduced calcium sensitivity of dihydropyridine binding to calcium channels might be a primary characteristic of this rat strain.

Animals↗
PubMed1991

Augmented Na,K-ATPase gene expression in spontaneously hypertensive rat hearts.

Abnormalities in cardiovascular Na,K-ATPase ion-transport function and regulation may play an important role in the pathogenesis of hypertension. However, it is not known whether these abnormalities are secondary to the effects of hypertension, such as increased pressure, or reflect an intrinsic abnormality in Na,K-ATPase gene expression and regulation. A genetic model of hypertension was used to address this issue. Na,K-ATPase alpha subunit gene expression in hearts was compared between spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Pre-hypertensive, 4-week old SHR hearts exhibited an approximately 4 fold elevation in alpha 1 and 8 fold elevation in alpha 2 mRNA levels compared with age-matched WKY hearts. These SHR mRNA levels remained almost equivalent throughout the development of hypertension at 8 and 16 weeks of age. WKY alpha 1 and alpha 2 mRNA levels exhibited a progressive increase during the same time period. The neonatal alpha 3 mRNA isoform was detected only in pre-hypertensive (4-week) SHR hearts. We conclude that cardiac Na,K-ATPase alpha subunit gene expression is significantly altered in SHR even before the onset of hypertension. These findings suggest that an abnormality in cardiac Na,K-ATPase gene expression constitutes an early, if not primary, event in spontaneous hypertension.

Animals↗
PubMed1990

Calcium binding to extracellular sites of skeletal muscle calcium channels regulates dihydropyridine binding.

The binding of dihydropyridine (PN200-110) to skeletal muscle microsomes (which were 84% sealed inside-out vesicles) was not influenced by the addition of calcium or magnesium nor by addition of their chelators (EDTA or EGTA) unless the vesicles were pretreated with the calcium-magnesium ionophore A23187 and EDTA to remove entrapped cations. Separation of inside-out vesicles from right-side-out vesicles by wheat germ agglutinin chromatography revealed that only the right-side-out vesicles exhibited a calcium-, magnesium-, and chelator-dependent binding of PN200-110. Dihydropyridine binding to cardiac sarcolemma membranes (which were 46% inside-out) and to solubilized skeletal muscle membranes was inhibited by EDTA and could be fully restored by 10 microM calcium or 1 mM magnesium. Calcium increased PN200-110 binding to partially purified rabbit skeletal muscle calcium channels from 3.9 pmol/mg protein to 25.5 pmol/mg protein with a pK0.5 = 6.57 +/- 0.059 and a Hill coefficient of 0.56 +/- 0.04. Magnesium increased binding from 0.7 pmol/mg protein to 16.8 pmol/mg protein with a pK0.5 = 3.88 +/- 0.085 and a Hill coefficient of 0.68 +/- 0.074. These studies suggest that calcium binding to high affinity sites or magnesium binding to low affinity sites on the extracellular side of skeletal muscle T-tubule calcium channels regulates dihydropyridine binding. Further, similar calcium and magnesium binding sites exist on the cardiac calcium channel and serve to allosterically regulate dihydropyridine binding.

Animals↗
PubMed1989

Solubilization, purification and characterization of lysoplasmalogen alkenylhydrolase (lysoplasmalogenase) from rat liver microsomes.

Alkenylhydrolase (EC 3.3.2.2; EC 3.3.2.5) has been purified 200-fold to a specific activity of 8.0 mumol/min per mg from rat liver microsomes with 51% of the activity recovered. Purification was accomplished by solubilization of the membrane-associated enzyme with octylglucoside and chromatographic resolution on sequential DEAE cellulose and hydroxylapatite (HPLC) columns in the presence of octylglucoside. The partially purified enzyme, specific for the 2-deacylated plasmalogen, lysoplasmalogen (1-alk-1'-enyl-sn-glycero-3-phosphocholine or -ethanolamine), had no hydrolytic activity with intact plasmalogens or 1-acyl-sn-glycero-3-phosphoethanolamine. Kinetic analyses of enzymic activity demonstrated apparent Km values of 5.5 and 42 microM for 1-alk-1'-enyl-sn-glycero-3-phosphocholine and 1-alk-1'-enyl-sn-glycero-3-phosphoethanolamine, respectively. The Vmax values were 11.7 and 13.6 mumol/min per mg with the choline and ethanolamine substrates, respectively. The optimal pH range was between 6.6 and 7.1 with both substrates; the energy of activation for the purified enzyme was 15,200 cal. The enzyme required no cofactors and was unaffected by low millimolar concentrations of Ca2+, Mg2+, Mn2+ or EDTA. It was inhibited by the sulfhydryl-reacting reagent, p-chloromercuribenzoate. Mono- or diradylglycerophospholipids or sphingomyelin did not affect the enzymic activity at 37 degrees C. Activity of the purified enzyme, destroyed by freezing at -20 degrees C, was preserved if stored at this temperature in the presence of 300-600 microM diradylglycerophosphocholine or 50% glycerol. A continuous spectrophotometric assay, adapted in our laboratory for the assay of liver alkenylhydrolase, facilitated this purification. This is the first reported purification of alkenylhydrolase.

Animals↗
PubMed1988

Solubilization and reconstitution of voltage-dependent calcium channel from bovine cardiac muscle. Ca2+ influx assay using the fluorescent dye Quin2.

Highly purified sarcolemmal membranes, prepared from fresh bovine heart left ventricle, were solubilized by n-octyl beta-D-glucopyranoside and reconstituted into proteoliposomes with soybean phospholipids by the detergent-dialysis method. Ca2+ flux into the proteoliposomes was determined using the fluorescent probe Quin2. A membrane potential (negative in the proteoliposome interior) that was created by K+ diffusion mediated by valinomycin accelerated the Ca2+ influx. The voltage-dependent Ca2+ influx was dependent on pretreatment of the sarcolemmal membranes with Bay K 8644 and was inhibited by various calcium antagonists including nicardipine (K0.5 = 4.5.10(-7) M), verapamil (K0.5 = 9.2.10(-9) M), diltiazem (K0.5 = 26.10(-8) M) and omega-conotoxin (K0.5 = 9.5.10(-9) M).

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1988

A study of liver regeneration using fetal rat liver tissue transplanted into the spleen.

The liver morphology of fetal hepatic tissue transplanted into an ectopic location was investigated over one year period. Fetal liver fragments prepared from a maternal rat on the 18th or 19th day of pregnancy were injected into the splenic parenchyma of syngeneic rats using a 21 gauge needle. Histologically, the fetal liver did not essentially show any apparent lobular architecture or cord structure. The transplanted fetal hepatic tissues survived and formed hepatic cords in the spleen instead of undergoing degeneration and necrosis. Three characteristic features became complete during the 4 weeks following transplantation, namely; clumps of hepatocytes with obvious hepatic cords and sinusoids, markedly proliferating bile ducts and proliferating individual hepatocytes. Macroscopic nodules of the hepatocytes on the spleen were seen at about 6 months after transplantation. When the differentiation of the transplanted fetal hepatic tissue was compared with the development of a normal neonatal liver after birth, it was delayed by only about one week, while there was no proliferation of bile ducts in the normal neonatal liver. This experimental model provides a useful system for investigating liver regeneration and the mechanism of cell growth.

Animals↗