IMPACT OF AN ACUTE TEMPERATURE-CHANGE ON PERFORMANCE AND METABOLISM OF PICKEREL (ESOX-NIGER) AND EEL (ANGUILLA-ROSTRATA) HEARTS

Mechanical performance, oxygen consumption (MO2), and the maximal activities of key enzymes of energy metabolism were assessed in chain pickerel (Esox niger) and American eel (Anguilla rostrata) hearts over a temperature range normally experienced by these fish. Ventricle strips from pickerel could be paced up to 48 contractions min-1 at both 5-degrees and 15-degrees-C. Eel ventricle strips responded at 48 contractions min-1 at 15-degrees-C but at 5-degrees-C could not be paced faster than 18 contractions min-1. At low temperatures, time to 50% relaxation was especially prolonged in eel ventricle strips, and increases in extracellular calcium resulted in large increased in resting tension. These findings suggest that calcium extrusion from the myocyte is impaired. Maximum output of perfused, isolated pickerel hearts occurred at frequencies of 30 and 36 contractions min-1 at 5-degrees and 15-degrees-C. Values for eel hearts were 18 and 30 contractions min-1. Pickerel hearts had the same power output at both temperatures. Power output of eel hearts was lower at 5-degrees than 15-degrees-C. Oxygen consumption of perfused hearts displayed a Q10 of about 1.9 for both pickerel and eel. Maximal in vitro activities of hexokinase, carnitine acyl-CoA transferase, citrate synthase, and ATPase were determined at 5-degrees and 15-degrees-C. Comparison of Mo2 values with enzyme activities reveals that the catalytic potential to provide ATP is in excess of resting energy demand at both temperatures. The impairment of eel heart performance at low temperature cannot be attributed to an inability to metabolize glucose or fatty acids. The findings with isolated preparations are consistent with maintenance of activity by pickerel and presumptive in situ cardiac function over a wide temperature range and with the lack of activity displayed by eel at low temperature in association with known reduced cardiac performance.