Volume regulation by red blood cells from brown trout

Regulatory volume decrease, following physical swelling of red cells from brown trout Salmo trutta, was almost complete in oxygenated cells but much less in deoxygenated cells. There was a small, insignificant regulatory volume increase, following physical shrinkage. Amiloride had no effect on this response, indicating that hypertonic shrinkage did not activate the Na+/H+ exchanger. However, cell volume was increased markedly in shrunken cells by addition of noradrenaline, with deoxygenated cells showing complete recovery. These data show that the previously reported differences in volume regulation between the red cells of brown trout and rainbow trout Oncorhynchus mykiss are not present and that both species appear to have lost volume sensitivity of the Na+/H+ exchanger. (C) 2001 The Fisheries Society of the British Isles.