Heterogeneity of peptides released by electrically active neuroendocrine caudodorsal cells of Lymnaea stagnalis

Abstract

The peptidergic caudodorsal cells (CDC) are located in the cerebral ganglia (CG) of the snail Lymnaea stagnalis. They have the periphery of the intercerebral commissure (COM) as the neurohaemal area. Release of the ovulation hormone (CDCH) and other presumed peptides by electrically active CDC was studied in vitro using CG/COM preparations which were preincubated with radioactive amino acids. Electrical activity of the CDC was induced by electrical stimulation of these cells, and by adenosine 3',5'-cyclic phosphate (cAMP) or potassium depolarization. Four classes of radioactively-labelled peptides are released by active CDC. They have molecular weights of greater than or equal to 6000, approximately 5500, approximately 4500 and approximately 2500 daltons, respectively. Released CDCH bioactivity co-eluted with the approximately 4500 dalton radioactive peptides. Selective removal of CDC demonstrated that the CDC release these peptides. cAMP and potassium depolarization also induce release of these peptides. The release after potassium depolarization is dependent upon the presence of calcium ions. CG/COMs from juvenile snails are not capable of releasing the peptides. With Bio-Gel P-6 chromatography, sodium dodecyl sulphate urea polyacrylamide electrophoresis, isoelectric focusing and proteolytic enzymes it was found that released CDCH is a peptide with the same molecular weight and pI as CDCH stored in the COM (molecular weight approximately 4700; pI approximately 9.3).