Sarcoplasmic reticulum: a key factor in cardiac contractility of sea bass Dicentrarchus labrax and common sole Solea solea during thermal acclimations.

This study investigated the effects of acclimation temperature upon (i) contractility of ventricular strips (ii) calcium movements in ventricular cardiomyocytes during excitation-contraction coupling (ECC), and (iii) the role of the sarcoplasmic reticulum (SR) in myocardial responses, in two marine teleosts, the sea bass (Dicentrarchus labrax) and the common sole (Solea solea). Because of the different sensitivities of their metabolism to temperature variation, both species were exposed to different thermal ranges. Sea bass were acclimated to 10, 15, 20, and 25 °C, and common sole to 6, 12, 18, and 24 °C, for 1 month. Isometric tension developed by ventricular strips was recorded over a range of physiological stimulation frequencies, whereas the depolarization-induced calcium transients were recorded on isolated ventricular cells through hyperpotassic solution application (at 100 mM). The SR contribution was assessed by ryanodine (RYAN) perfusion on ventricular strips and by caffeine application (at 10 mM) on isolated ventricular cells. Rates of contraction and relaxation of ventricular strip, in both species, increased with increasing acclimation temperature. At a low range of stimulation frequency, ventricular strips of common sole developed a positive force-frequency relationship at high acclimation temperature. In both the species, SR Ca(2+)-cycling was dependent on fish species, acclimation temperature and pacing frequency. The SR contribution was more important to force development at low acclimation temperatures in sea bass but at high acclimation temperatures in common sole. The results also revealed that high acclimation temperature causes an increase in the maximum calcium response amplitude on ventricular cells in both the species. Although sea bass and common sole occupy similar environments and tolerate similar environmental temperatures, this study indicated that sea bass and common sole can acclimatize to new thermal conditions, adjusting their cellular process in a different manner.