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  • Growth rate  (2)
  • glycogen phosphorylase  (2)
  • Springer  (4)
  • 1
    ISSN: 1573-4919
    Keywords: glycogen phosphorylase ; alloxan-diabetes ; cardiomyocytes ; G-protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The basis for the hypersensitive response of glycogen phosphorylase to epinephrine stimulation was investigated in adult rat cardiomyocytes isolated from normal and alloxan-diabetic animals. To assess potential G-protein involvement in the response, normal and diabetic derived myocytes were incubated with either cholera or pertussis toxin prior to hormonal stimulation. Pretreatment of cardiomyocytes with cholera toxin resulted in a potentiated response to epinephrine stimulation whereas pertussis toxin did not affect the activation of this signaling pathway. To determine if the enhanced response of phosphorylase activation resulted from an alteration in adenylate cyclase activation, the cells were challenged with forskolin. After 3 hr in primary culture, diabetic cardiomyocytes exhibited a hypersensitive response to forskolin stimulation relative to normal cells. However, after 24 hr in culture, both normal and diabetic myocytes responded identically to forskolin challenge. The present data suggest that a cholera toxin sensitive G-protein mediates the hypersensitive response of glycogen phosphorylase to catecholamine stimulation in diabetic cardiomyocytes and this response which is present in alloxan-diabetic cells and is induced in vitro in normal cardiomyocytes is primarily due to a defect at a post-receptor site.
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  • 2
    ISSN: 1573-4919
    Keywords: glycogen phosphorylase ; alloxan-diabetes ; cardiomyocytes ; cGMP ; phosphodiesterase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The focus of this study was to identify the molecular basis for the hypersensitive response of glycogen phosphorylase activation to epinephrine stimulation in alloxan diabetic-derived cardiomyocytes. Cyclic AMP levels were found not to be significantly different between normal and diabetic-derived cells while cGMP concentrations were found consistently to be significantly lower in diabetic-derived cells than in normal cells. Treatment with cyclic GMP analogues did not affect phosphorylase activation by epinephrine in normal cardiomyocytes whereas, IBMX, a nonselective phosphodiesterase inhibitor, had a significant effect on basal and agonist-stimulated phosphorylase activity in both normal and diabetic-derived cardiomyocytes. Differences in the time course for the rate of decay of phosphorylasea from agonist-stimulated to basal levels were observed between normal and diabetic cells. After 3 h in primary culture, phosphorylasea activity returned to basal levels more quickly in normal than in diabetic-derived cells while after 24 h in culture, the time for phosphorylasea decay was not significantly different between normal and diabetic myocytes and was longer than the 3 h response. After 3 h in primary culture, no significant difference in phosphorylase kinase activity was observed between normal and diabetic-derived cells exposed to epinephrine whereas, after 24 h in culture, phosphorylase kinase activity was significantly decreased in diabetic cells under basal and agonist-stimulated conditions. These data collectively suggest that the hypersensitive response of glycogen phosphorylase to epinephrine stimulation in diabetic-derived cardiomyocytes is not due to a defect present at the level of phosphorylase kinase but may, in part, result from an alteration in cardiac phosphodiesterase activity resulting from diminished intracellular cyclic GMP concentrations.
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  • 3
    ISSN: 1573-5133
    Keywords: Amazonia ; Batoidea ; Brazil ; Captive breeding ; Chondrichthyes ; Colombia ; Elasmobranchii ; Freshwater adaptation ; Growth rate ; Potamotrygonidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis Observations of reproductive features and body measurements were made on wild-caught, freshwater stingrays, Potamotrygon circularis and P. motoro, from the Amazon drainage of western Brazil and southern Colombia. Further observations were made in Detroit's Belle Isle Aquarium on a captive pair of P. motoro and their descendants, which constitute the first known captive breeding colony of potamotrygonids. The gross structure and function of female and male reproductive systems are described. There is no obvious difference between those of the two species. They are aplacentally viviparous, the young being nourished in advanced stages by uterine milk secreted by trophonemata. Size at onset and completion of sexual maturation, breeding season and behavior, gestation period, litter size and sex ratios are discussed. Up to 21 proportional measurements were made on several fetal and postnatal stages of both species. Several proportional changes occur in very early fetal life, but most body proportions undergo only minor changes from advanced fetal through adult stages. A growth curve is proposed for P. motoro based on observations of the captive colony.
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  • 4
    ISSN: 1573-5133
    Keywords: Batoids ; Chondrichthyes ; Costa Rica ; Elasmobranchs ; Euryhalinity ; Freshwater adaptation ; Growth rate ; Isolation of population ; Nicaragua
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis Of a total of 377 Pristis perotteti tagged in the Lake Nicaragua-Río San Juan System, 214 (56.8% were recovered. Eighty were recovered at the original tagging site; four moved downstream the full length of the river; and 127 tagged at the source of the river were recovered in all parts of the lake. Only one was recovered in a different river system, 58 km down the coast from the main mouth of the Río San Juan. A life span of 30 years is suggested, with rapid growth (30–40 cm per year) in the first three years, slowing to about 4 or 5 cm per year in the later years of life. Maximum sizes collected were 384 cm for males, 429 cm for females, smaller than maximum lengths reported elsewhere. The lake sawfish are not physically landlocked, but individuals remain in fresh water for very long periods; parturition takes place in fresh water; all sizes are found in the lake; and it appears that this stock finds all of its ecological needs met in the lake. Individuals may spend all of their lives in fresh water, although, as a species, P. perotteti has not completely abandoned the sea, since some are known to occur in salt water. The Lake Nicaragua-Río San Juan sawfish are a discrete stock, with only limited gene flow with neighboring stocks. P. perotteti is farther along in its adaptation to fresh water, in being able both to osmoregulate and reproduce there, than other known euryhaline elasmobranchs, except for the African stingray, Dasyatis garouaensis, of the Niger-Benue System, and the completely adapted South American freshwater rays (family Potamotrygonidae).
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