STIMULATED TRANSPORT OF ADENOSINE, GUANOSINE AND HYPOXANTHINE IN CRITHIDIA-LUCILIAE - METABOLIC MACHINERY IN WHICH THE PARASITE HAS A DISTINCT ADVANTAGE OVER THE HOST

Nutritional insufficiency is a common environmental extreme to which p arasitic protozoa are routinely exposed. In this study of purine salva ge mechanisms we illustrate some successful adaptations of the parasit e Crithidia luciliae to its environment, particularly in the case of p urine stress. In purine-depleted conditions, the insect trypanosome C. luciliae has the ability to increase the rates of transport of adenos ine, guanosine and hypoxanthine and the activity of the exoenzyme 3'nu cleotidase (3'NTase) during the growth cycle. The dramatic increase in these activities appears after a 72-h period in culture. The increase d activity of the purine transporters and 3'NTase could be suppressed by addition to the medium of a purine supplement such as adenosine or hypoxanthine (100 mu M). Under conditions where the concentration of p urines in the medium could be closely regulated, C. luciliae grown in purine-replete medium (greater than or equal to 75 mu M purine) exhibi ted low rates of purine transport and activity of 3'NTase. In comparis on, parasites transferred to medium with a low purine source (less tha n or equal to 7.5 mu M adenosine) had levels of adenosine, guanosine a nd hypoxanthine transport elevated 25-40-fold. The results link the si multaneous increase in activity of the nucleoside and base transporter s, 3'NTase activity and a general increase in the purine salvage of C. luciliae to the concentration of purines available at any time to the parasite. (C) 1997 Australian Society for Parasitology. Published by Elsevier Science Ltd.