Biochemical evidence of the sodium influx stimulating related peptide in the brain of the leech Theromyzon tessulatum

This paper reports the immunocytochemical and biochemical evidence of a sodium influx stimulating related peptide (SIS-like peptide) in the brain of the leech Theromyzon tessulatum. Cells immunoreactive to both polyclonal antisera raised against the N-terminal (fragment 10-19) or the C-terminal (fragment 67-76) sequences of the purified freshwater snail Lymnaea stagnalis sodium influx stimulating peptide (SISP) was detected in the brain of this leech. These immunocytochemical data were strengthened by biochemical results at the level of the protein and by in vitro translated RNA. By combined techniques i.e. high performance gel permeation chromatography, electrophoresis followed by immunoblot analysis with the two antisera and immunoprecipitation, we established the existence in leeches of a protein of ca 11 kDa and its precursor, a protein of ca 13 kDa related to the SISP. Moreover, results of injections of anti-SISP (10-19) preadsorbed or not with its homologous antigen to Theromyzon tessulatum confirmed the SIS-like substance involvement in osmoregulation by an anti-diuretic function.