Regulation of Cl- secretion in seawater fish (Dicentrarchus labrax) gill respiratory cells in primary culture

1. Primary cultures of sea bass (Dicentrarchus labrax) gill cells grown on permeable membranes form a highly differentiated tight epithelium composed of respiratory-like cells. This preparation was also found to provide a functional model for investigating the hormonal regulation of Cl- secretion. 2. In control conditions, i.e. in the absence of hormones or other stimuli, the cultured epithelium showed a short-circuit current (I-sc) of 8.8 +/- 0.4 mu A cm(-2), a transepithelial potential (V-t) of 28.6 +/- 0.6 mV (serosal side positive), and a transepithelial resistance (R-t) of 5026 +/- 127 Omega cm(2). Addition of 50 nM PGE(2) caused a stimulation of I-sc, V-t and transepithelial conductance, G(t). The increase in I-sc was probably due to the elevation in Cl- secretion, since it could be correlated with the stimulation of serosal to mucosal Cl-36(-) flux. Application of the neurohypophyseal peptide arginine vasotocin (AVT; 50 nM) or the beta-adrenergic agonist isoproterenol (isoprenaline; 0.5 mu M) evoked a stimulation in Cl- secretion, as was shown by the increases in I-sc and G(t). The excitatory effect of isoproterenol followed by the inhibitory action of propranolol, a beta-adrenergic antagonist, suggested the presence of beta-adrenergic receptors. Noradrenaline (0.1 mu M) elicited a reduction in I-sc, V-t and G(t), which was counterbalanced by the addition of phentolamine, an alpha-adrenergic antagonist. This suggested an activation of alpha-adrenergic receptors. 3. This study provides evidence for hormonal control of the Cl- secretion in sea bass gill respiratory cells in culture, involving AVT, prostaglandin (PGE(2)), and beta- and alpha-adrenergic receptors.