CATECHOLAMINE RELEASE IN HEAT-STRESSED ANTARCTIC FISH CAUSES PROTON EXTRUSION BY THE RED-CELLS

Two species of Antarctic fish were stressed by moving them from seawat er at -1 degrees C to seawater at 10 degrees C and holding them for a period of 10 min. The active cryopelagic species Pagothenia borchgrevi nki maintained heart rate while in the benthic species Trematomus bern acchii there was an increase in heart rate. Blood pressure did not cha nge in either species. Both species released catecholamines into the c irculation as a consequence of the stress. P. borchgrevinki released t he greater amounts, having mean plasma concentrations of 177 +/- 54 nm ol.l(-1) noradrenaline and 263 +/- 131 nmol.l(-1) adrenaline at 10 min . Pla.sma noradrenaline concentrations rose to 47 +/- 14 nmol.l(-1) an d adrenaline to 73 +/- 28 nmol.l(-1) in T. bernacchii. Blood from P. b orchgrevinki was tonometered in the presence of isoprenaline. A fall i n extracellular pH suggests the presence of a Na+/H+ antiporter on the red cell membrane, the first demonstration of this in an Antarctic fi sh. Treatment with the beta-adrenergic antagonist drug sotalol inhibit ed swelling of red blood cells taken from temperature-stressed P. borc hgrevinki, suggesting that the antiporter responds to endogenous catec holamines.