Abstract
Antarctic fish have the highest serum osmolarity of teleosts, approaching 600mOsm/L. This elevated osmolarity is a unique thermal adaptation of fishes living south of the Antarctic convergence. Upon warming these fish from -2C to +4C for four weeks, their serum osmolarity drops by 20%. This enhanced hypo-osmoregulation is due to increased activity of the Na/K-ATPase enzyme in the mitochondria rich chloride cells of the gill (J. Exp. Biol., 198: 2279). The regulation of chloride cell function in Antarctic fish has not been explored. Gills were excised from Trematomus bernacchii acclimated at -2C and perfused to remove RBCs. Chloride cell suspensions were formed through a series of scraping and sieving the gill filament tissue. Six million cells were placed in a micro-chamber with a Clark oxygen electrode. The basal rate of oxygen consumption was 1.7% oxygen consumed/hour/million cells (SEM = 0.18, n = 18). Head kidney tissue containing interrenal gland was extracted with a 0.8 M solution of HCl in ethanol and water (75/25, v/v). It was adsorbed to C18 SEP-PAK cartridges, and eluted with a mixture of acetonitrile and water (80/20, v/v) containing trifluoroacetic acid (0.1%). This extract resulted in a 41% (SEM = 14, n = 6) increase in the basal rate of oxygen consumption. This increase in oxygen consumption suggests that the head kidney of Antarctic fish contains a factor that modulates chloride cell function in vitro.