VASOPRESSIN STIMULATES TRANSLOCATION OF PROTEIN-KINASE-C IN THE TOAD URINARY-BLADDER

Incubation of the toad bladder epithelia with 100 nM 12-O-tetradecanoy lphorbol 13-acetate (TPA) for 1, 3 and 5 min decreased cytosolic prote in kinase C (PKC) activity to 85, 80 and 75% of control, while membran e-associated PKC activity increased to 127, 140 and 126% of control, r espectively. Long-term treatment of epithelial cells with TPA caused d ownregulation of PKC with a loss of 80% of the enzymic activity. Incub ation with vasopressin (AVP) for 2 min decreased cytosolic PKC activit y by 20%, whereas the activity in the membrane fraction increased by 3 3%. PKC translocation did not occur when epithelia were stimulated wit h [deamino(1)-D-arginine(8)]-vasopressin which binds more specifically to the V-2 receptor. Staurosporine inhibited PKC activity as well as the effect of AVP on translocation. Phorbol esters decreased the respo nse to AVP on water transport, whereas staurosporine greatly increased the hormonal response. We conclude that TPA induces an intracellular translocation and downregulation of PKC. The translocation of PKC by A VP and the inhibition of AVP-stimulated water flow by TPA suggest a si gnificant negative feedback loop involving PKC to modulate the action of AVP.