COORDINATION OF METABOLISM, ACID-BASE REGULATION AND HEMOCYANIN FUNCTION IN CEPHALOPODS

The role of cephalopod haemocyanins in oxygen transport is analysed in the light of the coordination of metabolism, acid-base regulation and gas exchange processes Results obtained in squid, the most active amo ng cephalopod species, indicate that the pH dependence of their haemoc yanin supports a Po-2-buffer function for the pigment. The release of base equivalents from the tissue during aerobic exercise and the minim al release of protons during anaerobic octopine formation protect arte rial pH and, thus, oxygen binding. The extent of respiratory acidifica tion and haemocyanin deoxygenation on the venous side is higher in blo od returning from the mantle than From the head. In vivo blood gas mea surements reported for squid and for other cephalopod species support the conclusion that CO2 accumulation and respiratory acidification of the blood occur in excess of the effect expected from the consumption of haemocyanin bound O-2 and RQ values derived from protein catabolism . This suggests that a considerable fraction of the oxygen consumed by the animal enters via the skin, especially in the mantle. Model calcu lations demonstrate that skin O-2 uptake in the mantle increases durin g activity in squid. In other cephalopod species like cuttlefish, the special process of arterial CO2 binding to oxygenated haemocyanin and its release during venous deoxygenation may provide the excess CO2 req uired For venous acidification. All of these processes allow the class ical Bohr effect to function supporting oxygen loading at the gills an d oxygen unloading in the tissues. The large pH-dependent cooperativit y and the Bohr effect combine to maximize the Po-2-buffer function of the respiratory pigment. These adaptations probably evolved after the ancestors of modern cephalopods lost their shells and locomotor activi ty assumed a greater role in their lifestyle.