FLUORESCENCE ANALYSIS OF THE INTERACTION OF ISOMETAMIDIUM WITH TRYPANOSOMA-CONGOLENSE

Isometamidium chloride (Samorin) is the only compound recommended for prophylaxis against bovine trypanosomiasis in sub-Saharan Africa. The fluorescence property of this compound was used to investigate the int eraction of the molecule with in vitro-derived bloodstream forms of Tr ypanosoma congolense IL 1180. Incubation of isometamidium with trypano somes at 37-degrees-C for 180 min resulted in a gradual alteration of the lambda(max.) with time (from 600 to 584 nm) and an increase in the intensity of trypanosome-associated fluorescence of approx. 2-fold. T he alteration in fluorescence was temperature-dependent and inhibited by the addition of N-ethylmaleimide. In contrast, with intact cells ad dition of digitonin caused a rapid increase in fluorescence intensity to approximately four times that observed with intact cells. Uptake of isometamidium was also determined using radiolabelled drug; the resul ts indicated that the time course of the uptake process resembled the fluorescence profile and was temperature-dependent. The results theref ore indicate that the alteration of fluorescence is due to interaction of isometamidium with an intracellular component(s) and that isometam idium is transported across the plasma membrane via a protein carrier. The data also indicate that the described fluorescence technique can be used to investigate the role of membrane transport in resistance to isometamidium.