Agnathans

1. Agnathans

2. Family overview: Lampreys may not look like fish, but they are. Their round, sucking mouth, lack of pectoral and pelvic fins, and eel-like body make lampreys appear very different from “typical” fish. They also have a unique life history, going through a transformation, or metamorphosis, from larva to adult. In Pennsylvania, the sea lamprey (Petromyzon marinus) naturally runs up the Delaware River from the Atlantic Ocean to spawn. It is also present in Lake Erie and the other Great Lakes. Sea lampreys bypassed the barrier of Niagara Falls after the Welland Canal was built. By the 1920s, they had spread all the way to the upper Great Lakes. Thus, although natives of the Delaware watershed, they are non-native to the Great Lakes and Lake Erie. Sea lampreys feed by attaching themselves by their concave, round, suction-disk mouth to the exterior of fish. They rasp a hole in the skin with their rough tongue, and feed on the host fish’s body fluids. They may kill their host directly, or weaken it so much that fungus infections and other ills destroy it. The sea lamprey invasion of the Great Lakes caused disastrous declines in lake trout and whitefish populations, affecting commercial and sport fisheries. Great Lakes tributary streams where sea lampreys spawn are treated with a chemical to reduce this damaging parasite’s numbers. Sea lampreys have little effect on native fishes in the Delaware River because the adult parasitic form inhabits the Atlantic Ocean.

3. THE ABSENCE OF RAPID CHLORIDE/BICARBONATE EXCHANGE IN LAMPREY ERYTHROCYTES

4. To determine whether carbon dioxide transport properties and distributions of ions in the blood of the lamprey support the view of the anion exchanger being absent in rbc

5. Tissues - C02 diffuses into rbc and combines with water to eventually produce bicarb and proton with the help of carbonic anhydrase • More bicarb diffuses into plasma, causing increase in proton concentration in rbc. Chloride ion moves in rbc

6. Model: • At tissues, carbon dioxide diffuses into rbc where it is hydrated to form bicarb and H+ (which binds to Hb). Bicarb not transported to plasma but carried in rbc to the gills. • At gills, oxygenation of Hb releases H+, which then combines with bicarb, forming CO2.

7. Results • CO2 dissociation curves for rbc, plasma and whole blood - at high pCO2, rbc’s have the highest CO2 content (fig 1)

8. Rbc’s also had the highest buffering capacity out of three samples (samples were exposed to acidification and alkalinization) • Rbc’s proved to have highest buffering capacity

9. Comparison of rbc pH and plasma pH - no significant difference (protons passively distributed across membrane) • 2,4-Dinitrophenol (DNP), C6H4N2O5, is a cellular metabolic poison. It uncouples oxidative phosphorylation by carrying protons across the mitochondrial

10. Distribution ratio of sodium, potassium, chloride ions and protons across rbc membrane against plasma pH (only protons changes according to plasma pH), not chloride and chloride concentrations very low in rbc

12. CO2 content was lower than either rbc or whole blood because the bicarb does not enter plasma and stays in rbc (fig1) • Rbc has the highest buffering capacity (fig2) • In mammals rbc pH is maintained by sodium/proton exchange mechanism. In lampreys, pH of rbc’s was not affected by DNP which suggests passive distribution across rbc membrane (fig3) • Distribution ratios of Chloride ions and protons are significantly different (fig 4)

13. In rbc’s with anion exchanger, an increase in rbc Cl- concentration with decreasing pH would cause water to be pulled into rbc osmotically • In lamprey blood, distribution ratio of Cl- did not significantly change and the water content of rbc did not vary over the pH studied (fig 5). • This indicates a constant rbc volume.

15. Homework • What does this study of a living agnathan tell us about the evolution of gas transport by the vertebrate erythrocyte?