Cyclic AMP modulation of active ion transport in the pigmented rabbit conjunctiva

This study was conducted to determine whether active ion transport in the pigmented rabbit conjunctiva was subjected to cyclic AMP modulation. 8-BrcAMP and compounds that may affect intracellular cAMP levels were tested for their effects on the conjunctival short-circuit current (I-sc) following mucosal application. Conjunctival I-sc was increased by 1 mM 8-BrcAMP, 0.001-20 mu M forskolin, 0.01-2 mM theophylline, 2 mu M l-epinephrine, and 20 mu M terbutaline in a Cl--containing but not in a Cl--free medium. The increase in I-sc induced by 1 mM 8-BrcAMP was reversed by 1 mM N phenylanthranilic acid, suggesting enhancement of Cl- secretion by cAMP. Similarly, the increase in I-sc induced by 20 mu M terbutaline was blunted by 1 mu M timolol, suggesting a role for beta(2) adrenergic modulation of Cl- secretion. Collectively, these results are consistent with the notion of cAMP modulation of conjunctival active ion transport.