EFFECTS OF DIFFERENT TYPES OF ACIDOSIS AND CA2+ ON CARDIAC CONTRACTILITY IN THE FLOUNDER (PLEURONECTES-FLESUS)

In contrast to most other fish the isolated myocardium of flounder (Pleuronectes flesus) was able to maintain contractility well under acidosis. The response to acidosis was biphasic, the initial force decline being followed by spontaneous recovery under ongoing acidification. This reaction took place only under hypercapnia and did not appear when extracellular pH was decreased to the same extent by lowering bicarbonate. Biphasic response to hypercapnia was more pronounced with low than with high extracellular Ca2+. A depressed sensitivity towards extracellular Ca2+ was seen in hypercapnia in contrast to acidification by lowering bicarbonate. This indicates that hypercapnia in inducing severe intracellular acidification, triggers an efficient compensatory reaction which is modified by Ca2+-availability. © 1979 Springer-Verlag.