The interaction between O2 and CO2 movements during aerobic exercise in fish

RESUMO

In resting rainbow trout, 99 per cent of the total CO2 excreted across the gills consisted of bicarbonate (HCO3-) dehydrated to CO2 in the red cell. This value decreased to 93 percent during exercise, the remainder being excreted as molecular CO2 which existed in the pre-branchial blood. HCO3- dehydration consumes a proton which can be supplied from hemoglobin (1-1b) through its buffer capacity or the Haldane effect. Bohr proton release from Hb upon oxygenation is maximal between 50 and 100 percent of Hb saturation, consistent with observations made in tench blood. At low swimming speeds, when venous blood 02 content (CvO2) was high, there was a small but insignificant acidosis as blood passed through the gills, indicating a greater release of protons than could be consumed by HCO3-. At higher swimming speeds, when CvO2 was low, there was a significant alkalosis in the arterial blood relative to the venous blood, indicating that fewer protons were released upon oxygenation than HCO3- ions were dehydrated to CO2. The disproportionate release of Bohr protons over the range of Hb-O2 saturation in the blood at the gills limits HCO3- dehydration during greater work loads, conserving the HCO3- buffer capacity of the blood and tissues.