Carbon dioxide transport and ion distributions were examined in the blood of the lamprey, Petromyzon marinus. Over the PCOCO2 range studied, the erythrocytes had the highest total CO2 content, followed by whole blood and true plasma. The nonbicarbonate buffer values were −37.0mequiv l−1 pH unit−1 for erythrocytes, −3.3 mequiv 1−1 pH unit−1 for whole blood and −0.1 mequiv 1−1 pH unit−1 for true plasma. These results are in sharp contrast to the models of carbon dioxide transport in the blood of other vertebrates and are consistent with the view that chloride/bicarbonate exchange is virtually absent in agnathan erythrocytes. Protons are passively distributed in Petromyzon blood. However, the distribution ratio for chloride between plasma and erythrocytes was strikingly different fromthe distribution ratio for protons. In the absence of rapid chloride/bicarbonate exchange, the erythrocyte volume is relatively constant over the physiological pH range. A model is presented to explain carbon dioxide transport in lamprey blood which does not involve a rapid chloride/bicarbonate exchange mechanism on the erythrocyte membrane.

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