Heart performance, Ca super(2+) regulation and energy metabolism at high temperatures in Bathygobius soporator, a tropical marine teleost

Experiments were conducted with Bathygobius soporator (Gobiidae), a small tropical marine teleost which lives in tide pools along the east coast of South America. In whole animals, VO sub(2) remained constant from 25 to 30 degree C and then increased until it reached a maximum value at 40 degree C of about 160 ml/kg/h. The f sub(H) increased progressively and significantly from 25 to 35 degree C, at which f sub(H) reached its maximum value of about 225 beats/min. At 40 degree C, however, the f sub(H) decreased to a value similar to that recorded at 25 degree C. Twitch force and resting tension were determined for isolated ventricle strips. At an extracellular Ca super(2+) level of 1.25 mM a transition from 25 to 40 degree C resulted in a decrease in twitch force which was restored upon a return to 25 degree C. This restoration of twitch force did not occur at an extracellular Ca super(2+) concentration of 9.25 mM. At 25 degree C, increments in extracellular Ca super(2+) from 1.25 to 7.25 mM resulted in increases in twitch force development. However, at 40 degree C only resting tension increased in concert with elevations in Ca super(2+). At 25 degree C, twitch force declined as frequency was increased above 30 contractions/min and became irregular above 120 contractions/min. At 40 degree C, twitch force development remained constant at frequencies up to about 150 contractions/min and declined thereafter. Preparations were able to maintain rhythmic response up to about 240 contractions times min super(-1). An increase in in vitro assay temperature from 25 to 40 degree C resulted in an elevation of total ATPase activity. Citrate synthase was present in high activities with hexokinase and 3-hydroxyacyl coenzyme A (CoA) being detectable but at lower activities. Heart performance is fragile at high temperature and under conditions which lead to high intracellular Ca super(2+). A controlled decrease in heart rate at high temperature may have a protective effect in maintaining low levels of intracellular Ca super(2+).