Action potential, force and function of the sarcoplasmic reticulum in the anaerobic trout heart.

The electromechanical coupling mechanism was studied in anaerobic heart ventricle strips of rainbow trout which had been electrically stimulated to contraction at 12 contractions/min. The twitch force fell immediately upon the onset of anaerobiosis (5 mM sodium cyanide and N2). The duration and overshoot of the action potential were reduced, the duration only transiently however, since a recovery to the pre-anaerobic level occurred later on. A change of extracellular Ca2+ from 1.25 to 5 mM during anaerobiosis caused a prompt increase in twitch force, whereas the action potential duration and overshoot decreased, the former, again only for a short time. The action potential, measured in 14 mM K+ to block the initial sodium current, was not significantly affected by anaerobiosis, although the accompanying twitch force values were more than halved. The negative effects of anaerobiosis on contractility were not influenced by either ryanodine or caffeine, whereas they were reduced at an elevated extracellular concentration of Ca2+. The results suggest that the regulation of the cytoplasmic Ca activity of the trout heart is well maintained under anaerobic conditions although the contractility is strongly reduced.