In recent years considerable progress has been made towards an understanding of the action of C. perfringens enterotoxin. This enterotoxin produces all symptoms associated with one of the most common food poisonings in the United States. Our long-term objective is to obtain an understanding of the pathophysiological mechanism(s) by which enterotoxin acts on sensitive cells. We are interested in elucidating the action of C. perfringens enterotoxin for several reasons, including 1) the public health importance of C. perfringens food poisoning, 2) the uniqueness of the action and biochemical structure of C. perfringens enterotoxin which differentiates it from all other enterotoxins studied to date and 3) the possible use of the enterotoxin as a probe of intestinal brush border membrane structure and function. The proposed research will: 1) confirm the identity of a putative brush border membrane receptor for enterotoxin by use of immunoprecipitation, immunoblotting and membrane probes. This putative receptor will be purified by affinity chromatography and other biochemical techniques. We also will 2) examine, at the level of the electron microscope, morphological damage caused by enterotoxin, and the cellular location of enterotoxin will be determined by immunochemical localization. Additionally, this research will 3) examine more closely the transport alterations and possible molecular membrane changes caused by enterotoxin. Ion flux studies, ion channel-blockers, lipid and protein analyses (by TLC and SDS-PAGE, respectively), and regulatory-mechanism (e.g., protein kinases) studies will be used. Importantly, 4) we will further study the enterotoxin molecule itself, using epitope mapping (via antienterotoxin monoclonal antibodies), and chemical and enzymic modifications. Lastly, 5) the possible existence of an additional enterotoxin(s) will be determined.