Abstract
cAMP mediates many of the effects of vasopressin, prostaglandin E2, and β-adrenergic agents upon salt and water transport in the renal collecting duct. The present studies examined the role of cAMP-dependent protein kinase (PKA) in mediating these effects. PKA is a heterotetramer comprised of two regulatory (R) subunits and two catalytic (C) subunits. The four PKA isoforms may be distinguished by their R subunits that have been designated RIα, RIβ, RIIα, and RIIβ. Three regulatory subunits, RIα, RIIα, and RIIβ, were detected by immunoblot and ribonuclease protection in both primary cultures and fresh isolates of rabbit cortical collecting ducts (CCDs). Monolayers of cultured CCDs grown on semipermeable supports were mounted in an Ussing chamber, and combinations of cAMP analogs that selectively activate PKA type I vs. PKA type II were tested for their effect on electrogenic ion transport. Shortcircuit current (I(sc)) was significantly increased by the PKA type II-selective analog pairs N6-monobutyryl-cAMP plus 8-(4- chlorophenylthio)-cAMP or N6-monobutyryl-cAMP plus 8-chloro-cAMP. In contrast the PKA type I-selective cAMP analog pair [N6-monobutyryl-cAMP plus 8-(6-aminohexyl)amino-cAMP] had no effect on I(sc). These results suggest PKA type II is the major isozyme regulating electrogenic ion transport in the rabbit collecting duct.