BRAIN CREATINE-KINASE ACTIVITY DURING ONTOGENY OF THE CICHLID FISH OREOCHROMIS-MOSSAMBICUS AND THE CLAWED TOAD XENOPUS-LAEVIS, INFLUENCE OF GRAVITY

The development of creatine kinase (CK) activity was studied in the brain of cichlid fish and clawed toads. The activity of CK in the whole brain of the fish decreases immediately after hatching (stage 6) from values of about 135 nmol substrate cleaved/mg protein/min to a value of about 105 at stage 8 (5 days post hatch at 20-degrees-C). With the exception of a significant peak (125 nmol) between stages 9 and 10 (7 and 9 days respectively, post hatch at 20-degrees-C) and a small intermediate peak at stages 12 and 13 (about 10 days post hatch at 20-degrees-C) a constant level of about 100 nmol cleaved substrate is maintained until maturity. In contrast, CK activity was determined to be 3-fold higher in the whole brain of the clawed toad. With the exception of two significant peaks at stages 47 and 49 (5 and 12 days respectively, post fertilization at 23-degrees-C) a value of about 360 nmol was found during larval development and metamorphosis, as well as in the adult brain. In investigating the possible influence of gravity on CK activity during early ontogeny of the brain both animal species were exposed to hyper-gravity (3 +/- 1 g) for 7 days. A significant decrease of total CK activity of 20% was found in the fish brain and of about 5% in the toad. Changes in total CK activity during brain development, as well as after the influence of altered gravitational forces, suggests that this enzyme is well adapted to critical phases of brain development and reacts very sensitively during this period to changes in environmental conditions.