VASOACTIVE-INTESTINAL-PEPTIDE STIMULATES A CAMP-MEDIATED CL- CURRENT IN AVIAN SALT-GLAND CELLS

VIP plays an integral role in both protein and fluid secretion in many exocrine glands. By employing the perforated patch-clamp whole-cell r ecording technique we investigated the effects of VIP on membrane pote ntial and transmembrane currents in avian exocrine sail gland cells. P rior to application of VIP, sail gland cells had a resting membrane po tential close to -45 mV. When challenged with VIP (1-100 nM) a sustain ed depolarization to E(Cl)- was induced which was mimicked by the appl ication of cell-permeable cAMP analogues or forskolin (1 mu M). BY emp loying the voltage-clamp recording configuration a sustained increase in current was observed with a reversal potential which approximated E (Cl)-. Ionic substitution experiments confirmed that the current was a Cl- conductance which was inhibited by the Cl- channel blockers flufe namic acid and miflumic acid and by the inhibitory cAMP isomer, adenos ine-3',5'-cyclic monophosphthioate. Rp-isomer. Based on this, and the Fact that the kinetic properties of the Cl- current activated by VIP a re similar to those activated by cAMP, we propose that VIP-receptor in teraction results in the activation of a cAMP-dependent Cl- current.