INDUCTION OF SURFACE FLUIDITY IN TRICHINELLA-SPIRALIS LARVAE DURING PENETRATION OF THE HOST INTESTINE - SIMULATION BY CYCLIC-AMP IN-VITRO

The lateral diffusion (D-L) properties of the fluorescent lipid probe 5-N (octadecanoyl) aminofluorescein (AF18) inserted into the surface o f muscle-stage larvae of Trichinella spiralis were investigated by flu orescence recovery after photobleaching. AF18 was not free to diffuse laterally in dormant larvae, and this remained unchanged after larval activation in vitro with trypsin and bile. However, a significant incr ease in surface fluidity of the probe was demonstrated (%R = 74 . 5; D -L = 11 . 5 x 10(-9) cm(2)/sec) when larvae invaded intestinal epithel ial tissue following oral infection of mice. Membrane-permeant photoac tivatable caged cyclic AMP was used to analyse the putative mechanism responsible for this increase in lateral diffusion in the parasite sur face. Although incubation of larvae with 1-50 mu M caged cAMP had no e ffect on surface fluidity, incubation with 100 mu M caged cAMP induced a substantial increase in the lateral mobility of AF18 (%R = 64 . 3; D-L = 8 . 3 x 10(-11) cm(2)/sec) immediately following photo-activatio n of the caged messenger. This induced fluidity, however, was transien t and the larval surface reverted to immobility within 15 min. These o bservations constitute the first reported measurement of the fluid pro perties of the surface of intracellular parasites, the first demonstra tion of the parasite surface fluidity altering as a result of host cel l invasion and the first indication of a mechanism underlying changes in surface fluidity in parasitic helminths.