Role of Cyclic Amp-Dependent Protein Kinase (Pka) in Regulating Egg-Laying Hormone (Elh) Secretion From AplΥSia Bag Cells

Author: Wayne, Nancy L.

Source: Netherlands Journal of Zoology, Volume 44, Numbers 3-4, 1993 , pp. 588-598(11)

Publisher: BRILL

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Abstract:

The aim of the present work was to generate information that allows further exploration of mechanisms regulating release of egg-laying hormone (ELH) from neuroendocrine bag cells of Aplysia. To start, experiments that document the pattern of ELH secretion in response to an electrical afterdischarge from excised neural preparations maintained in vitro, as well as from freely-behaving animals arc described. Preliminary studies invcstigating the role of the cAMP second-messenger system in regulating ELH secretion are also discussed. Concentrations of ELH, from either medium (in vitro preparations) or hemolymph (in vivo preparations), were measured by radioimmunoassay. In both types of preparations, the electrical afterdischarge triggered ELH secretion, but peak levels were reached near the end of or following termination of the afterdischarge. All preparations showed prolonged durations of secretion that extended at least 43 min past the end of the afterdischarge, indicating that action potentials arc not required for maintaining secretion of ELH. What cellular processes regulate this prolonged secretion? The cAMP second-messenger system is a likely candidate because of its suggested role in excitation of bag-cell membrane and transport of secretory granules to bag-cell growth cones in culture. Treatment with the specific cAMP-dependent protein kinase (PKA) inhibitor RpcAMPS attenuated the amplitude and duration of ELH secretion, whereas the PKA stimulator Sp-cAMPS had no significant effects on secretion compared to untreated controls. These preliminary results suggest that: 1) PKA plays an important role in regulating ELH release; 2) Afterdischarge-induced PKA maximally stimulates ELH release such that further elevations in PKA do not enhance secretion.

Keywords: Aplysia; bag cells; cyclic AMP; egg-laying hormone; neuroendocrine; protein kinase; second-messenger; secretion

Document Type: Research article

DOI: http://dx.doi.org/10.1163/156854293X00647

Affiliations: 1: Department of Physiology, UCLA School of Medicine, 10833 Le Conte Ave., Los Angeles, CA 90024, U.S.A.

Publication date: 1993-01-01

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