HEART PERFORMANCE, CA2-METABOLISM AT HIGH-TEMPERATURES IN BATHYGOBIUSSOPORATOR, A TROPICAL MARINE TELEOST( REGULATION AND ENERGY)

Experiments were conducted with Bathygobius soporator (Gobbiidae), a s mall tropical marine teleost which lives in tide pools along the east coast of South America. In whole animals, VO2 remained constant from 2 5 to 30 degrees C and then increased until it reached a maximum value at 40 degrees C of about 160 ml.kg(-1).h(-1). The f(H) increased progr essively and significantly from 25 to 35 degrees C. at which f(H) reac hed its maximum value of about 225 beats.min(-1). At 40 degrees C, how ever, the fH decreased to a value similar to that recorded at 25 degre es C. Twitch force and resting tension were determined for isolated ve ntricle strips. At an extracellular Ca2+ level of 1.25 mM a transition from 25 to 40 degrees C resulted in a decrease in twitch force which was restored upon a return to 25 degrees C. This restoration of twitch force did not occur at an extracellular Ca2+ concentration of 9.25 mM . At 25 degrees C, increments in extracellular Ca2+ from 1.25 to 7.25 mM resulted in increases in twitch force development However, at 40 de grees C only resting tension increased in concert with elevations in C a2+. At 25 degrees C, twitch force declined as frequency was increased above 30 contractions.min(-1) and became irregular above 120 contract ions.min(-1). At 40 degrees C, twitch force development remained const ant at frequencies up to about 150 contractions.min(-1) and declined t hereafter. Preparations were able to maintain rhythmic response up to about 240 contractions.min(-1). An increase in in vitro assay temperat ure from 25 to 40 degrees C resulted in an elevation of total ATPase a ctivity. Citrate synthase was present in high activities with hexokina se and 3-hydroxyacyl coenzyme A (CoA) being detectable but at lower ac tivities. Heart performance is fragile at high temperature and under c onditions which lead to high intracellular Ca2+. A controlled decrease in heart rate at high temperature may have a protective effect in mai ntaining low levels of intracellular Ca2+. (C) 1998 Elsevier Science L td. All rights reserved.