Chapter 54 - Ion Transport Peptide

Abstract

Ion transport peptide (ITP) and its longer isoform ITPL are members of the crustacean hyperglycemic hormone family. They contain six conserved cysteine residues forming three intramolecular disulfide bridges. The ITP gene is composed of three to five exons that produce one ITP mRNA, and one or two ITPL mRNAs by alternative splicing. These isoforms share the N-terminal part, and are generally distinguished by the presence (ITP) or absence (ITPL) of an amidated C-terminus. ITP is expressed in several pairs of brain cells, some of which have projections to the corpora cardiaca, and ITPL is expressed in the thoracic ganglia and abdominal ganglia as well as the brain. ITP was originally isolated from the corpora cardiaca of the locust based on its action on chloride ion transport through the ileum. In addition to this antidiuretic effect, ITP and ITPL are thought to be concerned with the regulation of various biological processes, both as circulating neurohormones and as locally released neurotransmitters.