MODULATION OF CYCLIC-AMP PRODUCTION BY STRIAL MARGINAL CELLS FROM GERBIL IN CULTURE

To further investigate the role of marginal cells (MCs) in the secretion of endolymph and because of the limitations encountered in investigating these cells in vivo, we used primary cultures of MCs derived from explants of gerbil stria vascularis and investigated modulation of the adenylate cyclase-cyclic AMP system. After 10 days on type I collagen coated plastic dishes, a confluent monolayer of epithelial-like cells was obtained which exhibited the morphologic and immunohistochemical features of the native marginal cells. The cyclic AMP (cAMP) content was determined at 37 degrees C, after 5 min of incubation with various agents, in the presence of a specific inhibitor of type III cAMP-dependent phosphodiesterase, RO 20-1724. The adenylate cyclase-cAMP system was associated with beta(2)-adrenergic receptors. The cAMP content was increased by isoproterenol (23-fold), a beta-agonist, but not by octopamine, an alpha-agonist, and the affinity for ICI 118.551, a specific beta(2)-antagonist, was greater than for CGP 20712A, a specific beta(1)-antagonist (Kd: 0.03 X 10(-6) M and 15 X 10(-6) M respectively). The cAMP content was maximally increased by prostaglandin E(2) > beta(2)-adrenergic agonist >> vasopressine type 2 receptor agonist (26-, 23-, and 3-fold the basal cAMP content, respectively). The present study demonstrates that cultured marginal cells retain some of their in vivo properties including a modulated enzymatic cAMP system. This culture model should allow further in-depth investigation of the function of marginal cells.