AJP - Regulatory, Integrative and Comparative Physiology, Vol 253, Issue 6 838-R847, Copyright © 1987 by American Physiological Society
Extracellular Ca2+, force, and energy state in cardiac tissue of rainbow trout
S. P. Hansen and H. Gesser
Department of Zoophysiology, University of Aarhus, Denmark.
The importance of ATP and phosphocreatine (PCr) concentrations for
myocardial force development was examined in electrically paced ventricular
strips from rainbow trout. Three metabolic situations were studied
involving either an aerobic block (N2, 5 mM NaCN), both an aerobic and a
glycolytic block (1 mM iodoacetate), or no metabolic inhibitors. Increasing
extracellular Ca2+ from 1.25 to 5 mM enhanced twitch-force development in
all of these situations but caused no change in resting force or ATP and
PCr content, except for the noninhibited preparations for which PCr
increased. Anaerobiosis caused a decrease in the PCr concentration together
with a fall in twitch force and an increase in resting force. Notably the
changes in the contractile system associated with a given reduction in PCr
were smaller in the absence than in the presence of iodoacetate. The
results show that an increased Ca2+ availability stimulates the
twitch-force development also at markedly lowered levels of high-energy
phosphates. A maintained Ca2+ regulation appears to be one important reason
for this. Furthermore, glycolysis seems to protect contractility in a way
not reflected in the level of high-energy phosphates.
