Inhibition of cAMP- and Ca-dependent Cl- secretion by phorbol esters: inhibition of basolateral K+ channels

Am J Physiol. 1993 Jan;264(1 Pt 1):C161-8. doi: 10.1152/ajpcell.1993.264.1.C161.


Pretreating confluent T84 cells with the phorbol ester phorbol 12-myristate 13-acetate (PMA) inhibits adenosine 3',5'-cyclic monophosphate (cAMP)- and carbachol-induced Cl secretion. Both a sustained short-circuit current (Isc), seen after the addition of 50 microM 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (CPT-cAMP) and 100 microM 3-isobutyl-1-methylxanthine (IBMX), and a transient current, seen after the subsequent addition of 100 microM carbachol, are inhibited by 80% following pretreatment with 100 nM PMA for 2 h. Pretreatment with PMA has no effect on the level of cystic fibrosis transmembrane conductance regulator protein or apical cAMP-dependent Cl conductance. Carbachol does not induce an increase in apical Cl conductance. Basolateral K conductance was measured in monolayers treated with apical nystatin and exposed to a K gradient. Agonist-independent K conductance is 10-fold greater in Cl media than in gluconate media. Pretreatment with PMA inhibits agonist-independent K conductance by 57% in Cl media but stimulates K conductance by 1.9-fold in gluconate media. The addition of carbachol induces a transient increase in basolateral K conductance, and pretreatment with PMA inhibits the agonist-dependent K conductance by 66% in Cl media and by 92% in gluconate media. In Cl media, serosal barium, at 3 mM, inhibits agonist-independent K conductance but has no significant effect on the carbachol-induced conductance. In nonpermeabilized monolayers, serosal barium inhibits the cAMP-dependent Isc by 56% but has no effect on the carbachol-induced Isc. These results demonstrate that the primary effect of PMA on Cl secretion is not inhibition of apical Cl channels but inhibition of basolateral K channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Barium / pharmacology
  • Calcium / physiology*
  • Carbachol / pharmacology
  • Cell Line / physiology
  • Cell Membrane / metabolism
  • Chloride Channels
  • Chlorides / antagonists & inhibitors*
  • Chlorides / metabolism
  • Cyclic AMP / antagonists & inhibitors*
  • Cyclic AMP / metabolism
  • Cyclic AMP / pharmacology
  • Cystic Fibrosis Transmembrane Conductance Regulator
  • Electrophysiology
  • Membrane Proteins / drug effects
  • Membrane Proteins / metabolism
  • Nystatin / pharmacology
  • Potassium / antagonists & inhibitors
  • Potassium / physiology
  • Potassium Channels / drug effects*
  • Tetradecanoylphorbol Acetate / pharmacology*


  • Chloride Channels
  • Chlorides
  • Membrane Proteins
  • Potassium Channels
  • Cystic Fibrosis Transmembrane Conductance Regulator
  • Nystatin
  • Barium
  • Carbachol
  • Cyclic AMP
  • Tetradecanoylphorbol Acetate
  • Potassium
  • Calcium