Abstract:
Previous studies have shown that the erythrocytes of amphibians are much less likely to lyse in hyposmotic conditions as are the erythrocytes of mammals. Such resistance to lysing may be the result of volume regulating membrane transport systems in amphibian erythrocytes. To determine the role of these membrane transport systems, blood was collected from American bullfrogs (Rana catesbeiana) and mice (Mus museu/us) and erythrocytes were treated with one ofthe following specific membrane transport inhibitors: furosemide, 4,4'-diidothiocyanatostilbene-2,2'-disulphonic acid (DIDS), and [(dihydroindenyl)oxy] alkanoic acid (DIOA). After exposure to furosemide, DIDS, DIOA, or all the inhibitors together the osmolality of the solution at which 50 percent of the erythrocytes had undergone lysis (50% lysis) was determined for both bullfrogs and mice. Furosemide, an inhibitor of the K+/Cr cotransporter and the Na+/K+/Cr cotransporter, and DIDS, an inhibitor of anion exchange, caused a significant increase in the lysing of mouse erythrocytes, but had no significant effect on bullfrog erythrocytes. However, exposure of erythrocytes to DIOA, a potent inhibitor of the K+/Cr cotransporter, resulted in increased lysing of both mouse and bullfrog erythrocytes, with the effect being greater for mouse erythrocytes. Trials using all the
inhibitors together also resulted in increased bullfrog erythrocyte lysing. Thus, the disabling of only specific membrane transport systems in frog erythrocytes hinders the cells' ability to volume regulate. Additionally, the bullfrog erythrocytes appear to be less affected by the inhibition of membrane transport mechanisms than mouse erythrocytes. This suggests that bullfrog erythrocytes possess either additional volume regulatory membrane transport mechanisms or other means by which they tolerate hyposmotic environments.
