HEMOGLOBIN-FUNCTION IN THE LOPHOPHORATE PHORONIS-ARCHITECTA (PHORONIDA)

The function of hemoglobin-containing red blood cells in O2 transport and storage was examined in a tube-dwelling marine animal, Phoronis architecta. The maximal rate at which O2 could be transported by the circulation in one animal (almost-equal-to 0.014 g) was 0.0018-mu-mol O2 . h-1 in physical solution and 0.054-mu-mol O2 . h-1 by hemoglobin (both computed at PO2 = 150 mmHg). Oxygen consumption rates of an average animal ranged from 0.005 to 0.049-mu-mol O2 . h-1 at external O2 pressures from 2 to 150 mmHg, respectively. These data indicate that augmented transport of O2 by hemoglobin is necessary under all conditions for the animal to utilize its aerobic metabolic capacity. Although the animal is surrounded by anoxic sediment and some O2 loss is inevitable, the geometric arrangement of the O2 source (red blood cells) relative to the O2 sink (consuming tissue plus anoxic sediment) and the O2-unloading properties of the hemoglobin allow the animal to utilize a substantial quantity of the O2 transported by the hemoglobin. The hemoglobin also functions as an O2 store lasting approximately 15 min. Hydrogen sulfide, which is present in the surrounding sediment, appears to have no effect on reversible O2 binding by hemoglobin and does not significantly affect O2 consumption by the animals.