ATTENUATION OF PARASITE CAMP LEVELS IN T-CRUZI-HOST CELL-MEMBRANE INTERACTIONS IN-VITRO

Previous investigations have shown that the adhesion of T. cruzi plasm a membrane vesicles (PMV) to monolayers of host cell myoblasts and to immobilized heart muscle sarcolemma membranes (PAM) on polyacrylamide beads is mediated by the interaction of T. cruzi attachment sites with the muscarinic cholinergic and beta-adrenergic receptors of the host cell membrane. It has also been shown that this interaction is blunted by the specific antagonists of the mammalian receptors atropine and p ropranol, respectively. In the studies reported here, PAM also rapidly attached to swimming T. cruzi trypomastigotes in a complex, concentra tion-dependent fashion and binding isotherms showed that the equilibri um between free and bound PAM is rapidly reached within 2 minutes of i ncubation in physiologically balanced salt solutions. In this time fra me, trypomastigote cAMP levels are significantly reduced from steady s tate values within 30 seconds of the addition of PAM in a buffer syste m containing a diesterase inhibitor. Maximal attenuation of cAMP level s was measured between 1 and 2 minutes of the addition of PAM to T. cr uzi trypomastigotes. The degree of cAMP level attenuation was reduced by blocking PAM attachment with either atropine or propranol. On the b asis of these results we propose that a likely pathway for the negativ e parasite signal generated upon adhesion of host muscle cell membrane s to the surface of the flagellates is from the parasite's surface att achment sites directly to a Pertussis toxin sensitive inhibitory prote in Gi, thereby blunting adenyl cyclase activity and cAMP formation.