DIFFERENT RED-BLOOD-CELL CHARACTERISTICS IN A PRIMITIVE AGNATHAN (M-GLUTINOSA) AND A MORE RECENT TELEOST (O-MYKISS) INFLUENCE THEIR STRATEGIES FOR BLOOD CO2 TRANSPORT

This study examines how the different red blood cell (rbc) characteris tics in two lower vertebrates, the phylogenitically primitive hagfish and a more recent teleost, the rainbow trout, influence their strategi es for blood CO2 transport. Deoxygenation of the blood resulted in a s ignificant increase in rbe CO2 content in hagfish, but there were no s ignificant changes in the CO2 content of plasma or a hole blood under these conditions. In contrast, deoxygenation increased the CO2 content of the rbc, plasma and; whole blood in the trout. These results demon strate that the Haldane effect is much less important for CO: transpor t in the hagfish as compared to the trout. The relative importance of the rbe and plasma in blood CO2 transport were roughly similar in hagf ish and trout and were very different from that previously documented in another primitive vertebrate, the lamprey. In trout, however, the r ole of the rbe in CO2 carriage was increased upon the addition of the beta-adrenergic agonist isoproterenol (10(-5) M) to the blood. Taken t ogether, these results and these recently collected for lampreys demon strate that changes in rbe characteristics during vertebrate evolution have probably resulted in several important transitions in the strate gy for blood CO2 transport. (C) 1998 Elsevier Science Inc.