THE EFFECTS OF TEMPERATURE AND ADRENERGIC AGONISTS ON CARDIAC MYOCYTES OF PERCH (PERCA-FLUVIATILIS) IN CELL-CULTURE CONDITIONS

1. Isolated cardiac myocytes of perch, Peuca fluviatilis, were kept in culture conditions for 1-2 months at 12 or 22 degrees C. In the culture most myocytes flattened, lost their spindle-shaped morphology, protruded pseudopod-like branches and many of them started visible contractions in 1-2 weeks and continued beating for several months. Myocytes did not divide in the sparse cell population used. Typical intracellular structures could be seen in electron micrographs still after 1-2 months, but the sarcoplasmic organization became gradually more irregular in the culture. 2. Beat rates showed linear temperature relationship on the Arrhenius plot. Myocytes cultivated at 22 degrees C showed higher frequencies and slightly less dependence on temperature than myocytes cultivated at 12 degrees C (apparent activation energies (E(a),) 86 and 107 kJ/mol, respectively). 3. Temperature dependence of frequencies was related to the presence of added serum or adrenergic agonists: beta-adrenergic agonists increased the frequencies and rendered the cells less dependent on temperature; apparent activation energy was 43 kJ/mol for isoprenaline or adrenaline and 108 kJ/mol for noradrenaline and control group. 4. Heat tolerance was greater in myocytes cultivated at 22 degrees C than in myocytes cultivated at 12 degrees C, and the change in tolerance appeared in 12 h after the alteration of culture temperature and the increased tolerance was persistent after that. 5. It is suggested, that the processes of quick heat-hardening and of slower but persistent heat resistance acclimation developed in these cells in culture conditions but not the capacity acclimation, which seems to be dependent on adrenergic regulation of beat rate.