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N Lake

Publications and source records attributed to N Lake.

At least 19 recordsLinked to original sources
PubMed1998

Identification of a mitochondrial Na+/H+ exchanger.

The electroneutral exchange of protons for Na+ and K+ across the mitochondrial inner membrane contributes to organellar volume and Ca2+ homeostasis. The molecular nature of these transporters remains unknown. In this report, we characterize a novel gene (YDR456w; renamed NHA2) in Saccharomyces cerevisiae whose deduced protein sequence is homologous to members of the mammalian Na+/H+ exchanger gene family. Fluorescence microscopy showed that a Nha2-green fluorescent protein chimera colocalizes with 4',6-diamidino-2-phenylindole staining of mitochondrial DNA. To assess the function of Nha2, we deleted the NHA2 gene by homologous disruption and found that benzamil-inhibitable, acid-activated 22Na+ uptake into mitochondria was abolished in the mutant strain. It also showed retarded growth on nonfermentable carbon sources and severely reduced survival during the stationary phase of the cell cycle compared with the parental strain, consistent with a defect in aerobic metabolism. Sequence comparisons revealed that Nha2 has highest identity to a putative Na+/H+ exchanger homologue (KIAA0267; renamed NHE6) in humans. Northern blot analysis demonstrated that NHE6 is ubiquitously expressed but is most abundant in mitochondrion-rich tissues such as brain, skeletal muscle, and heart. Fluorescence microscopy showed that a NHE6-green fluorescent protein chimera also accumulates in mitochondria of transfected HeLa cells. These data indicate that NHA2 and NHE6 encode homologous Na+/H+ exchangers and suggest they may be important for mitochondrial function in lower and higher eukaryotes, respectively.

Amino Acid Sequence↗
PubMed1997

Immunocytochemical localization of taurine in the pineal organ and retina of an anadromous fish, Plecoglossus altivelis.

Light and electron microscopic immunolocalization of taurine, a sulfur-containing free amino acid, was investigated in the photoneuroendocrine pineal organ and the retinal photoreceptor and pigment epithelial layer of the ayu Plecoglossus altivelis, an anadromous fish. Intense immunostaining was found in the outer segments of pineal photoreceptors and retinal cone-like cells. Moderate but definite immunostaining was found in the cytoplasmic processes of pineal supporting cells, the outer segments of retinal rod-like cells, and the apical processes of pigment epithelial cells. Although the electron microscopic immunogold labeling was not completely coincident with the results of light microscopic immunostaining, concentrated immunogold particles appeared in the inner segments of photoreceptor cells, the cytoplasmic processes of pineal supporting cells, and the apical processes of pigment epithelial cells. These light and electron microscopic findings in taurine immunolocalization were discussed in relation to the functions of taurine known mainly from retinal physiology. It was suggested that the abundant taurine localization may be involved at least in the protection of photoreceptor outer segments against harmful factors, and in the transportation of nutrients and metabolites. The immunostaining for taurine is useful for the discrimination of different types of photoreceptor cells in the pineal organ and retina of fish.

Animals↗
PubMed1995

Immunocytochemical demonstration of taurine in the retina and pineal organ of the pigeon.

Taurine-like immunoreactivity (TLI) is found in the pigeon retina at high levels within cones, in select cells of the inner nuclear layer and in sublaminae of the inner plexiform layer. At the ultrastructural level a high density of immuno-gold particles in visualized in the ellipsoid, but not in the paraboloid area of the inner segment. It is present in perikarya and the presynaptic endings of cones, but not in postsynaptic cell processes. The immuno-gold particles are not associated directly with the synaptic vesicles. In the pineal organ TLI was confined to the so-called dark pinealocytes which are surrounded by only family stained light pinealocytes. Clusters of protein A-gold particles are located in the ergastoplasm between polyribosomes adjacent to fibrous proteins and in chains along filamentous structures. Granules, vesicles and membrane whorls, which originate from modified cilia remain unlabeled. The results are discussed on the basis of previous findings; a direct or indirect functional relationship of taurine to ATP-dependent processes is suggested.

Animals↗
PubMed1994

Excitatory cardiovascular and respiratory effects of baclofen in intact rats.

The rat has become the preferred animal model for study of the central control of the cardiorespiratory system. However, data in the literature suggest that the role of GABAB receptors in control of the respiratory timing may be different in rats from that in other species. Therefore in this study we investigated cardiorespiratory effects of repeated injections of 0.5 nM baclofen and 50 nM CGP35348, GABAB receptor agonist and antagonist, respectively, applied into the fourth ventricle of urethane-anesthetized intact, spontaneously breathing Wistar rats. Baclofen increased arterial blood pressure (ABP), heart rate, inspiratory time (Ti), and the rate of rise (Di/t) and peak amplitude of the integrated diaphragmatic EMG (Di). Expiration (Te) was unaffected. CGP35348 reversed the ABP and Di effects of baclofen and decreased Di/t and Te below their control values, whereas Ti remained prolonged. These excitatory effects of baclofen are consistent with previously reported effects of low i.v. doses of baclofen in cats, and suggest that GABAB receptors may modulate the depth and duration of inspiration. We conclude that the intact rat represents a suitable animal model for investigations of the integrated control of cardiorespiratory functions. To our knowledge this is the first investigation reporting excitatory effects of GABAB receptor stimulation on inspiratory activity in rats. The depressant effects of baclofen on the respiratory rhythm reported in the rat "isolated" brain in situ, and the neonatal rat brainstem--spinal cord in vitro seem to be unique for those specific preparations.

Animals↗
PubMed1994

Taurine depletion and excitation-contraction coupling in rat myocardium.

Although the sulfur-containing amino acid taurine is found in high concentrations in mammalian myocardium, its involvement in function of the cardiac myocyte remains unclear. To examine the effects of taurine depletion on cardiac mechanical function, rats were treated in vivo with the taurine transport antagonist guanidinoethane sulfonate (GES). After 6 weeks of treatment, myocardial taurine concentrations were decreased to < 40% of control, with no change in tissue DNA content. Right ventricular trabeculas from taurine-depleted rats exhibited significant reductions (P < .05) in isometric twitch force (Ft) at all [Ca2+]o levels and systolic sarcomere lengths examined. Taurine-depleted trabeculas also exhibited increased passive compliance. A slight (P < .05) rightward shift in the Ft-[Ca2+]o relation suggested a decrease in the sensitivity of the taurine-depleted muscles to [Ca2+]o. No changes were observed in the force-interval relation, suggesting that the transsarcolemmal Ca(2+)-handling mechanisms remained unchanged. The fraction of Ca2+ recirculated through the sarcoplasmic reticulum, inferred from the decay of postextrasystolic potentiation, was also not different in the taurine-depleted muscles. When force was expressed relative to the rate of stimulation, length of rest periods, or postextrasystolic potentiation, virtually all curves were super-imposable for control and taurine-depleted muscles, suggesting that the deficit was not dependent on Ca2+ handling. Thus, we conclude that in taurine-depleted muscles the force-generating processes showed the same regulation as in control muscle. Furthermore, the substantial deficit in force development is consistent with a reduced population of force generators on the basis of three pieces of evidence.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Loss of cardiac myofibrils: mechanism of contractile deficits induced by taurine deficiency.

It is well established that taurine deficiency is associated with myocardial contractile dysfunction; however, the mechanism is unknown. As a follow-up to finding reduced force generation in taurine-depleted rat cardiac trabeculae, using either calcium or strontium activation, this study examined alterations in ventricular fine structure and contractile proteins in animals made taurine deficient by in vivo treatment with a taurine transport antagonist, guanidinoethane sulfonate. Observations of ventricular ultrastructure showed disordered contractile filaments and clear losses of myofibrillar bundles in association with taurine deficiency. Biochemical analyses of ventricular contractile proteins using polyacrylamide gel electrophoresis confirmed losses of the major sarcomeric proteins, myosin and actin. These findings provide a possible mechanism for the contractile deficits and cardiomyopathy described in taurine-deficient animals.

Actins↗
PubMed1992

Taurine, GABA and GFAP immunoreactivity in the developing and adult rat optic nerve.

The localizations of taurine, gamma-aminobutyric acid (GABA) and glial fibrillary acidic protein (GFAP) within the developing rat optic nerve were determined using immunocytochemical techniques on tissues from animals ranging in age from embryonic day 20 to postnatal 28 days. Mature nerves from 3-4-month-old adults were also examined. At the younger ages, taurine immunoreactivity was intense and localized specifically to the optic nerve axons, but by postnatal day 15 and thereafter its predominant localization was in macroglia. Some of these glia were astrocytes as indicated by the specific marker, GFAP. GABA immunoreactivity was present at the same time as taurine but was found only in macroglia. In mature nerves the patterns of taurine, GABA and GFAP distribution (within glia) were highly similar.

Animals↗
PubMed1992

Immunocytochemical localization of taurine and glial fibrillary acidic protein in human optic nerve.

Taurine immunoreactivity (IR) in 1-microns sections of glutaraldehyde-fixed human optic nerve was observed using light microscopy and an antibody raised in rabbit to taurine conjugated to bovine serum albumin. Throughout the nerve, taurine-IR was prominent in glial cells, in their perinuclear regions, and in their numerous branching processes, some of which extended to the pial septa. The peripheral glial mantle (glia limitans) was densely stained, whereas axons and the pial septa showed relatively little or no taurine-IR. Immunoreactivity for glial fibrillary acidic protein (GFAP), and astrocyte-specific marker, was evaluated on adjacent sections. The pattern of GFAP-IR was highly similar to that for taurine, suggesting that a subset of taurine-immunoreactive glial cells are optic nerve astrocytes. To our knowledge, this is the first localization of taurine and GFAP in human optic nerve.

Adult↗
PubMed1991

Intracatheter streptokinase for recurrent peritonitis in CAPD.

Intracatheter streptokinase (SK) is advocated as effective treatment with minimal adverse effects in both recurrent bacterial peritonitis and catheter fibrin blockage in continuous ambulatory peritoneal dialysis (CAPD) patients. We reviewed 35 instillations in 20 patients noting a high (86%) side effect profile consisting of fever, onset of turbid dialysis effluent and/or abdominal pain. SK probably releases fibrin clot containing bacteria, leukocytes and debris from the colonized catheter into the peritoneal cavity causing a "peritonitis-like syndrome" of 1 to 3 days duration. Fungal peritonitis occurred after SK in 2 patients. Failure of SK therapy was encountered in Staphylococcus epidermidis infection (p less than 0.05 versus other organisms), which may be related to its protective capsular polysaccharide slime and ability to adhere to plastic prosthetic devices. SK, in this study, was useful treatment in relapsing bacterial peritonitis (50% overall cure) but failed to correct catheter malfunction.

Adult↗
PubMed1990

Effects of taurine depletion on intrinsic contractility of rat ventricular papillary muscles.

Contractile parameters in Krebs-Henseleit media containing various calcium concentrations were compared in left ventricular papillary muscles of two groups of rats: control and taurine depleted. All tests were carried out with the muscles at initial length, Lmax, the length that produced maximal active tension. From measurements of after- and un-loaded contractions, the velocity-tension curves and the derived maximum velocity of shortening were not different between the groups. Time to peak shortening and extent of shortening were not altered, while relaxation times and contraction duration were significantly prolonged for taurine-depleted muscles. Peak isometric tension and its rate of development were significantly reduced in taurine-depleted muscles compared with controls. Postrest (3 min) stimuli and paired stimuli (200-ms interval) evoked similar potentiated contractile responses in both groups, such that the ratio of their peak tensions remained unchanged. For taurine-depleted muscles the force-frequency relationship (a negative staircase) was parallel to, but lower than, control. These experiments suggest that taurine deficiency leads to reductions in action potential triggered calcium release from internal stores, and deficits in calcium sequestration. This may result from disfacilitation of calcium binding to the sarcoplasmic reticulum and other storage sites during taurine deficiency.

Animals↗
PubMed1990

Immunocytochemical localization of taurine within glial cells in the optic nerve of adult albino rats.

Taurine immunoreactivity in one micron sections of the adult rat optic nerve was observed using light microscopy. Prominent staining was seen in glial cell somata in the perinuclear region and in their processes throughout the nerve, particularly in endfeet on capillaries and in the peripheral basal lamina (glia limitans). Axons and blood vessels showed relatively little or no staining in the mature nerve. The pattern of glial fibrillary acidic protein immunoreactivity on subsequent sections was similar in many respects to that of taurine, suggesting that a sub-population of taurine immunoreactive glial cells are optic nerve astrocytes.

Animals↗