Affiliation:
1. Instituto de Investigaciones Cardiológicas, Facultad de Medicina y Cátedra de Biofı́sica, Facultad de Odontologı́a, Universidad de Buenos Aires-Consejo Nacional de Investigaciones Cientı́ficas y Técnicas, 1122 Buenos Aires, Argentina
Abstract
Tension-dependent (TDH) and tension-independent heat (TIH) release were measured during single isovolumetric contractions in the arterially perfused rat ventricle. Under perfusion with 7 mM K-0.5 mM Ca, TDH showed only one component (H3), whereas TIH could be divided into two components (H1 and H2) of short evolution (similar to the classically identified activation heat) and one component (H4) of long duration (dependent on mitochondrial respiration). Under 25 mM K, TIH components (i.e., H1, H2, and H4) increased with the increase in extracellular Ca concentration ([Ca]o) from 0.5 to 4 mM, and H3 correlated with pressure at all [Ca]o, with regression parameters similar to those observed under 7 mM K. Under 25 mM K-2 mM Ca, peak pressure development (P), H1, H2, and H3, plotted against the number of beats under 0.4 μM verapamil, exponentially decreased, but H4 decreased to 5.5 ± 2.9% in the first contraction and remained constant thereafter. Under hypoxia, P, H1, H2, and H3 progressively decreased for about six contractions, but H4 was not detectable from the second contraction. The results suggest that increasing extracellular K concentration decreases contractile economy mainly by increasing energy expenditure related to a Ca-dependent (verapamil-sensitive) mitochondrial activity that is not related to force generation.
Publisher
American Physiological Society
Subject
Physiology (medical),Cardiology and Cardiovascular Medicine,Physiology
Cited by
10 articles.
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