Light-Induced Changes in Cytosolic pH in Leaf Cells of Egeria densa: Measurements with pH-Sensitive Microelectrodes

Light-induced changes of cytosolic pH (pH_c) and the plasmalemmapotential (E_m) in dark-adapted leaf cells of the aquatic plant,Egeria densa were measured simultaneously with double-barreledpH-sensitive microelectrodes. Upon illumination, pH_c increasedtransiently and then decreased to a level that was lower thanthe original value, while the plasmalemma was greatly hyperpolarizedafter an initial small depolarization. DCMU inhibited the light-inducedchanges in both pH_c and E_m. DCMU acted without directly inhibitingthe electrogenic proton pump in the plasmalemma since a decreasein pH_c caused by treatment with butyrate (H⁺-loading) hyperpolarizedthe plasmalemma in DCMU-pretreated cells. N.N-Dicyclohexylcarbodiimide(DCCD) also inhibited the light-induced changes in both pH_cand E_m. This result may be explained by direct inhibition ofthe proton pump in the plasmalemma by DCCD since the decreasein pH_c caused by butyrate did not induce membrane hyperpolarizationin DCCD-treated leaf cells. Fusicoccin induced membrane hyperpolarizationand slight acidification of the cytosol. DCCD inhibited thefusicoccin-induced changes in both pH_c and E_m. The mechanismof the light-induced changes in pH_c is discussed in relationto activities of the proton pump in the plasmalemma and photosynthesis. (Received January 10, 1994; Accepted June 9, 1994)     

Chloroplast Development in the Chloroplast Ribosome Deficient Mutant (y-1 ac-20) of Chlamydomonas reinhardtii

To study the participation of chloroplast protein synthesisduring the three phases [Matsuda (1974) Biochim. Biophys. Acta366:45] of the greening process in Chlamydomonas reinhardtiiy-1, the greening characteristics in the low-chloroplast ribosomemutant y-1 ac-20 were compared with those in the y-1. In thedouble mutant cells Chl synthesis proceeded with an extendedlag and without a second transition point. The development ofpotential for rapid Chl synthesis (P-factor formation) was alsodelayed. Furthermore, PS I activity increased significantly,whereas PS II activity developed very little during greeningof the double mutant cells. The results indicate that greeningin double mutant cells occurs with no apparent late phase. (Received November 26, 1984; Accepted February 25, 1985)     

Short-term ascorbic acid deficiency induced oxidative stress in the retinas of young guinea pigs

We examined whether short-term ascorbic acid deficiency induces oxidative stress in the retinas of young guinea pigs. Four-week-old guinea pigs were given a scorbutic diet (20 g/animal/day) with and without adequate ascorbic acid (400 mg/animal/day) in drinking water for 3 weeks. The serum concentrations of the reduced form of ascorbic acid and the oxidized form of ascorbic acid in the deficient group were 14.1 and 4.1%, respectively, of those in the adequate group. The retinal contents of the reduced form of ascorbic acid and the oxidized form of ascorbic acid in the deficient group were 6.4 and 27.3%, respectively, of those in the adequate group. The retinal content of thiobarbituric acid-reactive substances, an index of lipid peroxidation, was 1.9-fold higher in the deficient group than in the adequate group. Retinal reduced glutathione and vitamin E contents in the deficient group were 70.1 and 69.4%, respectively, of those in the adequate group. This ascorbic acid deficiency did not affect serum thiobarbituric acid-reactive substances and reduced glutathione concentrations but increased serum vitamin E concentration. These results indicate that short-term ascorbic acid deficiency induces oxidative stress in the retinas of young guinea pigs without disrupting systemic antioxidant status.     

Photosynthetic control of the plasma membrane H+-ATPase in Vallisneria leaves. I. Regulation of activity during light-induced membrane hyperpolarization

In mesophyll cells of the aquatic angiosperm Vallisneria gigantea Graebner, red, blue, or blue plus far-red light induced a typical membrane hyperpolarization, whereas far-red light alone had little effect. Both N,N'-dicyclohexylcarbodiimide, a potent inhibitor of H+-ATPase, and carbonylcyanide m-chlorophenylhydrazone, an uncoupler, produced a considerable membrane depolarization in the dark-adapted cells and a complete suppression of the light-induced hyperpolarization. Although 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosynthetic electron transport, did not affect the membrane potential in darkness, it completely inhibited the light-induced membrane hyperpolarization. In vivo illumination of the leaves with red light caused a substantial decrease in the Km for ATP, not only of the vanadate-sensitive ATP-hydrolyzing activity in leaf homogenate, but also of the ATP-dependent H+-transporting activity in plasma membrane (PM) vesicles isolated from the leaves by aqueous polymer two-phase partitioning methods. The effects of red light were negated by the presence of DCMU during illumination. In vivo illumination with far-red light had no effect on the Km for ATP of H+-transporting activity. These results strongly suggest that an electrogenic component in the membrane potential of the mesophyll cell is generated by the PM H+-ATPase, and that photosynthesis-dependent modulation of the enzymatic activity of the PM H+-ATPase is involved in the light-induced membrane hyperpolarization.     

Association of a polymorphism of the CC chemokine receptor-2 gene with bone mineral density

The possible association of the 190G-->A (Val64Ile) polymorphism of the CC chemokine receptor-2 gene (CCR2) with bone mineral density (BMD) was examined in 2215 subjects (1125 men, 1090 women), all of whom were community-dwelling individuals aged 40 to 79 years. Among men aged < 60 years, BMD for the distal radius, lumbar spine, or Ward's triangle was significantly greater in those with the AA genotype than in those with the GG or GA genotypes. For postmenopausal women, BMD for the distal radius or femoral neck was significantly greater in those with the AA genotype than in those with the GG or GA genotypes. In contrast, for men aged > or =60 years and for premenopausal women, BMD was not associated with the CCR2 genotype. These results suggest that CCR2 may be a new candidate for a susceptibility locus for bone mass in middle-aged men and postmenopausal women.     

Rapid increase of vacuolar volume in response to salt stress

Suspension-cultured cells of mangrove [Bruguiera sexangula (Lour.) Poir.] showed a rapid increase in vacuolar volume under salt stress, although there was no change in the cell volume. The rapid increase in the vacuolar volume was an active process, which followed the activation of the tonoplast H(+)-ATPase and the vacuolar acid phosphatase. The same phenomenon was observed in barley (Hordeum vulgare L. cv. Doriru) root meristematic cells under salt stress but not in pea ( Pisum sativum L.). Increases in vacuolar volume could potentially protect the cytoplasm by decreasing the cytoplasmic volume during the initial phases of salt stress.     

Effects of cytokinin types and their concentrations on shoot proliferation and hyperhydricity in in vitro pear cultivar shoots

This study was made to clarify the effects of cytokinin type and their concentrations on shoot proliferation and hyperhydricity in in vitro Pyrus pyrifolia N. (`Hosui' and `Kosui') shoots. The shoots were subcultured in a woody plant medium supplemented with 0.5 M 3-indolyl-butyric acid, 3% (w/v) sorbitol, 0.8% (w/v) agar, and with cytokinins kinetin, 6-benzylaminopurine (BA), N-(2-chloro-4-pyridyl)-N9-phenylurea (CPPU), 1-phenyl-3-(1,2,3-thiadiazol-5-yl) urea (TDZ) added at concentrations 0.44, 4.40, 11.0 and 44.0 M. The highest number of shoots was induced by adding BA at concentration 11.0 M, then by 4.4 M BA, in both cultivars. TDZ and CPPU caused greater hyperhydricity in cultured explants than BA and kinetin. `Kosui' was more susceptible to hyperhydricity compared with `Hosui'.     

Mitochondrial haplogroup N9a confers resistance against type 2 diabetes in Asians

Because mitochondria play pivotal roles in both insulin secretion from the pancreatic beta cells and insulin resistance of skeletal muscles, we performed a large-scale association study to identify mitochondrial haplogroups that may confer resistance against or susceptibility to type 2 diabetes mellitus (T2DM). The study population comprised 2,906 unrelated Japanese individuals, including 1,289 patients with T2DM and 1,617 controls, and 1,365 unrelated Korean individuals, including 732 patients with T2DM and 633 controls. The genotypes for 25 polymorphisms in the coding region of the mitochondrial genome were determined, and the haplotypes were classified into 10 major haplogroups (i.e., F, B, A, N9a, M7a, M7b, G, D4a, D4b, and D5). Multivariate logistic-regression analysis with adjustment for age and sex revealed that the mitochondrial haplogroup N9a was significantly associated with resistance against T2DM (P=.0002) with an odds ratio of 0.55 (95% confidence interval 0.40-0.75). Even in the modern environment, which is often characterized by satiety and physical inactivity, this haplogroup might confer resistance against T2DM.     

Imatinib mesylate (STI-571) attenuates liver fibrosis development in rats

It is widely recognized that activated hepatic stellate cells (HSC) play a pivotal role in development of liver fibrosis. A platelet-derived growth factor (PDGF) is the most potent mitogen for HSC. The aim of this study was to examine the effect of imatinib mesylate (STI-571, Gleevec), a clinically used PDGF receptor (PDGFR) tyrosine kinase inhibitor, on development of experimental liver fibrosis. The rat model of pig serum-induced hepatic fibrosis was used to assess the effect of daily oral administration of STI-571 on the indexes of fibrosis. STI-571 markedly attenuated development of liver fibrosis and hepatic hydroxyproline and serum fibrosis markers. The number of alpha-smooth muscle actin-positive cells and mRNA expression of alpha2-(I)-procollagen, tissue inhibitor of metalloproteinases-1, and transforming growth factor-beta were also significantly suppressed by STI-571. Our in vitro study showed that STI-571 markedly attenuated PDGF-BB-induced proliferation and migration and alpha-SMA and alpha2-(I)-procollagen mRNA of activated HSC in a dose-dependent manner. STI-571 also significantly attenuated PDGF-BB-induced phosphorylation of PDGFR-beta, MEK1/2, and Akt in activated HSC. Because STI-571 is widely used in clinical practice, it may provide an effective new strategy for antifibrosis therapy.     

Overexpression of calmodulin induces cardiac hypertrophy by a calcineurin-dependent pathway

The possible role of calcineurin in cardiac hypertrophy induced by calmodulin (CaM) overexpression in the heart was investigated. CaM transgenic (CaM-TG) mice developed marked cardiac hypertrophy and exhibited up-regulation of atrial natriuretic factor (ANF) and beta-myosin heavy chain gene expression in the heart during the first 2 weeks after birth. The activity of calcineurin in the heart was also significantly increased in CaM-TG mice compared with wild-type littermates. Treatment of CaM-TG mice with the calcineurin inhibitor FK506 (1mg/kg per day) prevented the increase in the heart-to-body weight ratio as well as that in cardiomyocyte width. FK506 also inhibited the induction of fetal-type cardiac gene expression in CaM-TG mice. Overexpression of CaM in cultured rat cardiomyocytes activated the ANF gene promoter in a manner sensitive to FK506. Activation of a calcineurin-dependent pathway thus contributes to the development of cardiac hypertrophy induced by CaM overexpression in the heart.