Hypercapnic and hypocapnic hypoxia in the lugworm arenicola marina: A ³¹P NMR study

Using the noninvasive method of 31 P nuclear magnetic resonance(NMR) spectroscopy, the influence of hypoxia on intracellular pH (pH i ) and on the energy metabolism was studied in the lugworm Arenicola marina. 1. During hypercapnic hypoxia (induced by the animal itself), pH i dropped from 7.3 ± 0.1 (n = 6) to 6.5 ± 0.1 (n = 4) within 24 hours, whereas during hypocapnic hypoxia pH i decreased by only 0.3 units (n = 4). The change in pH w (pH of the ambient water) was similar: strong acidification from about 8.1 to 6.1 during hypercapnic and moderate acidification to 7.8 during hypocapnic hypoxia. 2. Mobilization of phosphagen (phosphotaurocyamine) occurred faster during hypercapnic than hypocapnic hypoxia. Anaerobic end products (propionate and acetate), however, accumulated to a greater extent during hypocapnic than hypercapnic hypoxia. 3. Conclusion: The severe acidosis found during hypercapnic hypoxia depends on the amount of CO 2 accumulation rather than on the amount of glycolytic end products. On the other hand, the lower accumulation of glycolytic end products and the faster mobilization of phosphagen with severe acidosis seem to reflect a regulatory effect of pH i on anaerobic metabolism.