IN-VITRO ANALYSIS OF VOLUME AND PH REGULATION IN THE RED-BLOOD-CELLS OF A PRIMITIVE AIR-BREATHING FISH, THE BOWFIN, AMIA-CALVA

In the bowfin (Amia calva), a decrease in extracellular pH in vitro was associated with an increase in the water content and chloride concentration in the red blood cells that could be inhibited by the anion-exchange blocker, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS). After a step increase in CO2 tension, the extracellular total CO2 concentration was also significantly reduced by DIDS. Finally, over most of the experimental pH range, the red blood cell pH observed in the presence of DIDS was significantly elevated compared with that of controls. Taken together, these results indicate that as in most other fishes, chloride-bicarbonate exchange is clearly present and functional in bowfin red blood cells. Moreover, within the physiological pH range, ion movements across the anion exchanger have a marked influence on both the volume and the pH of bowfin red blood cells. In sharp contrast to the rainbow trout (Oncorhynchus mykiss), catecholamines had no effect on the volume, pH, or intracellular sodium concentration of red blood cells in the bowfin. Following osmotic swelling, rainbow trout red blood cells were able to regulate their volume back to control levels within 2 h. In the bowfin, however, there was no regulation of red blood cell volume after osmotic swelling. Thus, in contrast to many other fishes examined to date, it would appear that in the bowfin, the physiological mechanisms involved in the adrenergic response and in the regulatory volume decrease after osmotic swelling may be less active or possibly even absent in the red blood cells.