Release of proteins and polysaccharides from the albumen gland of the freshwater snail Helisoma duryi : effect of cAMP and brain extracts

Abstract

The albumen gland is a compound tubular exocrine gland found in the female reproductive tract of freshwater pulmonate snails such as Helisoma duryi. It secretes a perivitelline fluid, composed of protein and polysaccharide complexes, and coats each fertilized egg. A 288-kDa native glycoprotein, composed of several 66-kDa subunits, was identified in soluble extracts of albumen gland. Forskolin stimulates the release of secretory granules, containing both proteins and polysaccharides, from the cytoplasm of the glandular cells. An acid extract of the central nervous system or the adenosine-3′,5′-cyclic monophosphate (cAMP) analogue 8-bromo cAMP, stimulates protein secretion from the gland. Pretreatment of the albumen gland with cAMP antagonist (R_p isomer of cAMP) inhibits the stimulatory effect of a brain extract. Digestion of brain extract with proteolytic enzymes abolishes its activity, suggesting the factor from the brain is peptidergic. The neuroactive agents serotonin, Phe-Met-Arg-Phe-amide, Tyr-Gly-Gly-Phe-Met-Arg-Phe-amide, small cardioactive peptide B, and caudodorsal cell hormone were also tested for potential secretion-promoting ability. Brain extracts were partially purified with a Sep-Pak C₁₈ reverse-phase cartridge and indicate the peptide is relatively hydrophobic. These results suggest that a brain peptide promotes the secretion of perivitelline fluid, and this is mediated by the adenylate cyclase/cAMP signal transduction pathway.