A role for second messengers in the control of activation-associated modification of the surface of Trichinella spiralis infective larvae

Abstract

The involvement of second messengers in the control of activation-induced changes to the surface of Trichinella spiralis infective larvae was investigated using membrane-permeant photo-activatable ‘caged’ compounds to alter intracellular levels of inositol trisphosphate (IP 3), calcium ions (Ca 2+) and cyclic AMP (cAMP). Activation of larvae by incubation in culture medium containing trypsin and bile was followed by the loss of the surface coat labelled with the fluorescent PKH26 lipid probe and this correlated with the reciprocal acquisition of surface lipophilicity detected using the fluorescent lipid probe octadecanoyl aminofluorescein (AF18). Optimal surface coat shedding and AF18 insertion was also achieved following photolysis of caged mediators liberating IP 3, Ca 2+ or cAMP within the parasite. Chelation of Ca 2+, however, abolished the effects of larval activation. Nevertheless, addition of cAMP (but not IP 3) to Ca 2+-depleted larvae overcame this inhibition and restored AF18 insertion to levels achieved by activated parasites. Therefore, the existence of a linear second messenger pathway involving the sequential release of IP 3, Ca 2+ and then cAMP is likely.