title: Feedback regulation of Na channels in rat CCT. IV. Mediation by activation of protein kinase C.
abstract: The hypothesis that feedback inhibition of the apical Na+ channels in the cortical collecting tubule (CCT) is mediated by activation of a Ca(2+)-dependent protein kinase was tested using the patch-clamp technique. Na+ channel activity was monitored in cell-attached patches in principal cells of split-open rat tubules. Mean number of open channels (NPo) and single-channel current (i) were measured at 37 degrees C during continuous tubule superfusion. Phorbol 12-myristate 13-acetate (PMA; 50 nM), an activator of protein kinase C (PKC), decreased NPo to 33% of the control value. Staurosporine (200 nM), an inhibitor of PKC and of Ca(2+)-calmodulin kinase II, practically abolished the effect of PMA. Ouabain (1 mM), reduced NPo to 29% of control values and decreased i. Ouabain did not downregulate the channels in tubules exposed to staurosporine, although it still reduced i. Incubation of the tubules with 10 microM KN-62, a specific cell membrane-permeable inhibitor of Ca(2+)-calmodulin kinase II, did not interfere with the ouabain-dependent downregulation of the channels. The results support the view that the downregulation caused by ouabain involves the Ca(2+)-dependent phosphorylation of the channel itself or of proteins regulating the channel.
authors.affiliation: Department of Physiology and Biophysics, Cornell University Medical College, New York, New York 10021, USA.
authors.forename: G
authors.initials: G
authors.lastname: Frindt
authors.forename: L G
authors.initials: LG
authors.lastname: Palmer
authors.forename: E E
authors.initials: EE
authors.lastname: Windhager
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D015536:Down-Regulation / Q000187:drug effects; D004789:Enzyme Activation; D005246:Feedback; D005260:Female; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010704:Phorbols / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D019311:Staurosporine / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D015854:Up-Regulation
chemical_list: D010704:Phorbols; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D010042:Ouabain; C063302:KN 62; D000584:Amiloride; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate; C033085:phorbol