Active cation transport and Na+K+Mg ATPase of the monotreme erythrocytes

The erythrocytes of the echidna (Tachyglossus aculeatus) and platypus (Ornithorhynchus anatinus), which are practically devoid of intracellular ATP content (1), were examined for active Rb86 influx and for the presence of Na+K+Mg ATPase. We found that intact erythrocytes of both species possess the ability to actively transport cations. Ouabain sensitive Rb86 influx in the echidna was approximately 0.17 mumoles/ml cells x hr, whereas the platypus exhibited a higher value of 0.43 mumoles/ml cells x hr. Surprisingly, ouabain sensitive Na+K+Mg ATPase activity of isolated membranes was high amounting to some 15 to 25 fold higher than the human erythrocyte counterpart determined under identical conditions. These findings suggest that a trace amount of ATP is sufficient to maintain active cation transport across the monotreme cell membranes.