Document Detail

The heart extrasystole: an energetic approach.
MedLine Citation:
PMID:  9887045     Owner:  NLM     Status:  MEDLINE    
The consequences of an extrasystole (ES) on cardiac muscle's energetics and Ca2+ homeostasis were investigated in the beating heart. The fraction of heat release related to pressure development (pressure dependent) and pressure-independent heat release were measured during isovolumic contractions in arterially perfused rat ventricle. The heat release by a contraction showed two pressure-independent components (H1 and H2) of short evolution and a pressure-dependent component (H3). The additional heat released by ES was decomposed into one pressure-independent (H'2) and one pressure-dependent (H'3) component with time courses similar to those of control components H2 and H3. ES also induced the potentiation of pressure development (P) and heat release during the postextrasystolic (PES) beat. The slope of the linear relationship between pressure-dependent heat and pressure maintenance was similar in control, ES, and PES contractions (0.08 +/- 0.01, 0.10 +/- 0.02, and 0.08 +/- 0.01 mJ. g-1. mmHg-1. s-1, respectively). The potentiation of H2 (heat component related with Ca2+ removal processes) in PES was equal to H'2 at 0.3, 0.5, 1, and 2 mM Ca2+, suggesting that the extra amount of Ca2+ mobilized during ES was recycled in PES. Pretreatment with 1 mM caffeine to deplete sarcoplasmic reticulum Ca2+ content inhibited both the mechanical and energetic potentiation of PES. However, the heat released and the pressure developed during ES were not changed by sarcoplasmic reticulum depletion. The results suggest that 1) the source of Ca2+ for ES would be entirely extracellular, 2) the Ca2+ entered during ES is accumulated in the sarcoplasmic reticulum, and 3) the Ca2+ stored by the sarcoplasmic reticulum during ES induces an increased contribution of this organelle during PES compared with the normal contraction.
F D Marengo; M T Márquez; P Bonazzola; J E Ponce-Hornos
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Publication Detail:
Type:  In Vitro; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  The American journal of physiology     Volume:  276     ISSN:  0002-9513     ISO Abbreviation:  Am. J. Physiol.     Publication Date:  1999 Jan 
Date Detail:
Created Date:  1999-03-05     Completed Date:  1999-03-05     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  0370511     Medline TA:  Am J Physiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  H309-16     Citation Subset:  IM    
Instituto de Investigaciones Cardiológicas, Facultad de Medicina y Cátedra de Biofísica, Facultad de Odontología, Universidad de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Técnicas, 1122 Buenos Aires, Argentina.
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MeSH Terms
Caffeine / pharmacology
Calcium / metabolism
Cardiac Complexes, Premature / metabolism*,  physiopathology
Energy Metabolism / physiology*
Heart / drug effects,  physiopathology
Homeostasis / physiology
Hot Temperature
Myocardial Contraction / physiology
Myocardium / metabolism*
Osmolar Concentration
Rats, Wistar
Sarcoplasmic Reticulum / metabolism
Reg. No./Substance:
58-08-2/Caffeine; 7440-70-2/Calcium

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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