Effect of acute temperature transitions on chronotropic and inotropic responses of the South American lungfish Lepidosiren paradoxa

摘要

The in vivo and in vitro cardiac responses of Lepidosiren paradoxes were analyzed during temperature variations from 25 degreesC (acclimation temperature) to 15degreesC and 35degreesC, and subsequent return to 25degreesC. Chronotropic (heart frequency) and inotropic (twitch force) responses varied directly with temperature, decreasing from 25degreesC to 15 degreesC and increasing from 25degreesC to 35 degreesC. However, time to peak tension (TPT) and time to half relaxation (THR) showed an inverse tendency. The results indicate that the myocardium of L. paradoxes responds more appropriately to acute elevations in temperature, which results in an increased cardiac performance due to both positive chronotropism and inotropism, in spite of the temperature-induced curtailment of TPT and THR.