EFFECTS OF THERMAL-ACCLIMATION ON VENTRICLE SIZE, PROTEIN-COMPOSITION, AND CONTRACTILE PROPERTIES OF CRUCIAN CARP HEART

1. The aim of the study was to find out how thermal adaptation affects ventricular size, protein composition and functional properties of th e contractile machinery of the fish heart. For that purpose crucian ca rp (Carassius carassius L.) were acclimated in laboratory to 2 degrees and 22 degrees C for three months. 2. Long-term acclimation to 2 degr ees increased-the relative ventricular mass by 86% in comparison to fi sh acclimated to 22 degrees C. 3. The cold-induced cardiac enlargement was associated with a remodelling of protein composition of the ventr icular muscle. Total concentration of proteins, including non-collagen ous proteins of myocytes and collagenous proteins of extracellular mat rix, was increased from 96 to 109 mg g(-1) (p < 0.05) tissue wet weigh t. The increase was exclusively due to increased concentration of coll agenous proteins, since concentration of sarcoplasmic proteins was unc hanged and concentration of myofibrillar proteins was reduced. Total h ydroxyproline concentration was lower in cold-acclimated animals; the elevated concentration of collagenous proteins is, therefore, not due to collagen but other proteins of the extracellular matrix. Thus, accl imation to cold increases protein concentration of extracellular matri x but reduces protein concentration of the myocytes in crucian carp he art. 4. Effects of caffeine (5 mM) on the contractile properties of ve ntricular myocardium were studied to find out if thermal acclimation a lters Ca activation of contraction. Caffeine increased force of contra ction more in the hearts of warm-acclimated (110%) than cold-acclimate d fish (40%). Furthermore, relaxation rate and time-course of contract ion were differently affected by caffeine in cold- and warm-acclimated fish. These findings suggest that thermal acclimation changes the fun ction of proteins responsible for excitation-contraction coupling.