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  • SAGE Publications  (3)
  • 1985-1989  (3)
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  • SAGE Publications  (3)
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  • 1985-1989  (3)
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  • 1
    Online Resource
    Online Resource
    Hypothesis Testing on a Proportional Reasoning Task by Children at Different Piagetian Stage Levels
    SAGE Publications ; 1986
    In:  International Journal of Behavioral Development Vol. 9, No. 1 ( 1986-03), p. 91-104
    Details
    In: International Journal of Behavioral Development, SAGE Publications, Vol. 9, No. 1 ( 1986-03), p. 91-104
    Abstract: The relationship between 7-, 9-, and 11-year-old children's performance on a battery of selected Piagetian measures and on a proportional reasoning task was examined. The proportional reasoning task, modeled after an hypothesis-testing probe procedure, was devised to identify the hypotheses and strategies children use when making proportional judgments. As expected, a strong relationship between stage level and (1) the complexity of hypotheses used, (2) the use of the proportional hypothesis, and (3) the overall use of logical hypotheses was found. Generally, only formal-operational children responded proportionally. Contrary to expectations, children were not responsive to feedback, i.e., they tended to generate and maintain the same hypothesis across trials regardless of feedback. The role of children's cognitive limitations, as well as how salient the feedback was, were discussed as possible explanations for this finding. Age and sex differences on the proportional reasoning task also were found. Possible directions for extension of this study to older children and adolescents were discussed.
    Type of Medium: Online Resource
    ISSN: 0165-0254 , 1464-0651
    URL: Article
    DOI: 10.1177/016502548600900106
    RVK:
    CL 1000
    Language: English
    Publisher: SAGE Publications
    Publication Date: 1986
    detail.hit.zdb_id: 1466999-7
    detail.hit.zdb_id: 432118-2
    SSG: 5,2
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  • 2
    Online Resource
    Online Resource
    Free Calcium in Rat Papillary Muscle at Contraction Assessed with Ca-Selective Microelectrodes
    SAGE Publications ; 1989
    In:  Angiology Vol. 40, No. 8 ( 1989-08), p. 736-742
    Details
    In: Angiology, SAGE Publications, Vol. 40, No. 8 ( 1989-08), p. 736-742
    Abstract: Direct measurements of free intracellular calcium (Ca)i are needed for an understanding of the regulation of contractility. An on-line measurement of (Ca)i with Ca-selective microelectrodes in intact muscle strips provides a suitable means of investigating this problem, although considerable methodologic difficulties exist. Measurements of (Ca)i concentrations during muscle contraction have been carried out by different methods such as Ca-binding techniques and aequorin luminescence, but remain unsatisfying, since they were not performed on intact muscle strips. The authors' measurements were carried out with Ca-selective microelectrodes on rat papillary muscles (stretched to optimal length in a perfusion bath of 1.54 mL at 30°C). The impalement of electrodes was considered adequate when the heights of Ca-electrode potential and membrane potential remained constant for more than twenty minutes. For provoking contractile responses, the authors replaced the normal Tyrode solution by a caffeine-containing contracture solution (content in mM: 0 NaCl [choline], 4 CaCl 2 , 30 KCI, 25 caffeine, 1.05 MgCl 2 ). Ca-se- lective microelectrodes were calibrated before and after each measurement and only those impalements were taken as adequate that showed identical calibration curves before and after the experiment. They measured the (Ca)i at 20%, 50%, and 80% of maximal contractile force and obtained (Ca)i concentrations of 1.1 ± 0.3 μM (at 20%), 3.6 ± 1.2 μM (at 50%), and 11.8 ± 0.27 μM (at 80%) (n=6, ±SEM). These results represent the first on-line measurements of the myocardial (Ca)i concentrations with Ca ++ selective microelectrodes in intact muscle strips during various degrees of contraction. It can be seen that contractile response does not occur below a (Ca)i concentration of 1 μM. Maximal contractile response is reached at (Ca)i concentrations beyond 10 μM.
    Type of Medium: Online Resource
    ISSN: 0003-3197 , 1940-1574
    URL: Article
    DOI: 10.1177/000331978904000809
    Language: English
    Publisher: SAGE Publications
    Publication Date: 1989
    detail.hit.zdb_id: 2065911-8
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  • 3
    Online Resource
    Online Resource
    Restriction by Nitrendipine of Excessive Concentration of Free Intracellular Calcium Ions in Ventricular Myocardium of Hypertensive Rats
    SAGE Publications ; 1988
    In:  Angiology Vol. 39, No. 3 ( 1988-03), p. 246-252
    Details
    In: Angiology, SAGE Publications, Vol. 39, No. 3 ( 1988-03), p. 246-252
    Abstract: In earlier investigations it has been found that high arterial blood pressure of salt-sensitive DAHL rats (DAHL-S) that received a diet con taining 8% NaCl could be normalized by chronic treatment with specific calcium antagonists, as for instance, nitrendipine or anipamil. Parallel measurements on heart and arterial vasculature with atomic absorption spectrometry revealed that there was a rise in absolute calcium content upon development of hypertension, whereas under the influence of ni trendipine, not only the blood pres sure and heart weight but also myocardial (and arterial) tissue cal cium content remained in the physio logic range. In the present study, an additional determination of the free intracellu lar calcium ion concentration with Ca-sensitive microelectrodes was car ried out. For technical reasons, the measurements were restricted to iso lated resting rat papillary muscles (stretched to optimal length in a per fusion bath of 1.5 ml at 30°C in nor mal Tyrode solution). The impale ment of the electrodes was considered adequate when the heights of Ca po tential and membrane potential were constant for more than twenty min utes. In order to produce severe sys temic hypertension, a group of six-week-old DAHL-S rats was fed with an 8% NaCl diet over five weeks. Another group of DAHL-S rats received additionally 150 mg/kg nitrendipine twice a day orally. Salt- resistant DAHL-R rats, also fed with an 8% NaCl diet, served as controls. The findings of this preliminary study are as follows (n = 5 in each group):
    Type of Medium: Online Resource
    ISSN: 0003-3197 , 1940-1574
    URL: Article
    DOI: 10.1177/000331978803900307
    Language: English
    Publisher: SAGE Publications
    Publication Date: 1988
    detail.hit.zdb_id: 2065911-8
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