Influence of temperature on calcium sensitivity in the ventricular myocardium of the South American lungfish: Effects of extracellular calcium and adrenaline

The mechanical properties of ventricular myocardium of the South American lungfish, Lepidosiren paradoxa, acclimated to 25 °C, were evaluated in vitro at 15, 25 and 35 °C. The inotropism (Fc-% of initial values) of ventricle strips was examined in response to adrenaline (from 10−8 to 10−5 M) and extracellular calcium (from 2.5 to 14.5 mM) in all experimental temperatures. At 15 and 25 °C, Fc rose when extracellular Ca2+ or adrenaline were increased, while Fc remained unchanged at 35 °C. These results suggest that at lower temperatures Ca2+ availability is a limiting step to cardiac performance and can be ameliorated by adrenergic stimulation. In contrast, since inotropic agents failed to increase cardiac inotropism at 35 °C, lungfish myocytes seem to show a high temperature sensitivity, which increases Ca2+-buffering capacity and/or Ca2+ transportation from and to cytosol as well as myofilaments Ca2+ sensitivity.