Summary
300 μM vanadate (NH4VO3) caused an about 65% increase in force of contraction in isolated electrically driven cat papillary muscles. The positive inotropic effect (PIE) was accompanied by only a small (about 20%) but significant increase in c-AMP levels. 0.3 μM isoprenaline (ISO) produced a much greater increase in c-AMP levels (about 80%) while the PIE of ISO was as great as the PIE observed with 300 μM NH4VO3. In cat right ventricular adenylate cyclase preparations NH4VO3 and ISO stimulated adenylate cyclase activity by nearly the same extent. Propranolol (1 μM and 5 μM) prevented the ISO-induced adenylate cyclase stimulation but not the stimulation due to NH4VO3. Phosphodiesterase activity was not affected by NH4VO3 (up to 1000 μM). It is concluded that the small vanadate-induced increase in c-AMP levels, which is due to adenylate cyclase stimulation, inintact papillary muscles maycontribute to its PIE, but other mechanisms may be at least equally important.
Zusammenfassung
300 μM Vanadat (NH4VO3) steigerte an isolierten, elektrisch gereizten Katzenpapillarmuskeln die Kontraktionskraft um ca. 65%. Der positiv inotrope Effekt (PIE) ging einher mit einem nur geringen (ca. 20%), aber signifikanten Anstieg des c-AMP-Gehaltes. 0.3 μM Isoprenalin (ISO) verursachte einen sehr viel größeren Anstieg des myokardialen c-AMP-Gehaltes (ca. 80%), während der PIE von ISO gleich groß war wie der PIE von NH4VO3. In einer Adenylatcyclasepräparation von rechten Ventrikeln des Katzenherzens stimulierten NH4VO3 und ISO die Adenylatcyclaseaktivität in nahezu gleichem Ausmaß. Propranolol (1 μM und 5 μM) verhinderte die Aktivierung der Adenylatcyclase durch ISO, aber nicht die Aktivierung durch NH4VO3. Die Phosphodiesteraseaktivität wurde durch NH4VO3 (bis zu einer Konzentration von 1000 μM) nicht beeinflußt. Aus den Ergebnissen wird geschlossen, daß der geringe vanadatinduzierte c-AMP-Anstieg, der über eine Stimulation der Adenylatcyclase zustande kommt, zwar am Zustandekommen des PIE beteiligt sein mag, daß aber andere Mechanismen von mindestens ebenso großer physiologischer Bedeutung sind.
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This work was supported by the Deutsche Forschungsgemeinschaft.
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Schmitz, W., Hackbarth, I., Scholz, H. et al. Effects of vanadate on the c-AMP system of the heart. Basic Res Cardiol 75, 438–443 (1980). https://doi.org/10.1007/BF01908408
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DOI: https://doi.org/10.1007/BF01908408