Cytochrome P-450 metabolites mediate extracellular Ca(2+)-induced inhibition of apical K+ channels in the TAL

Am J Physiol. 1996 Jul;271(1 Pt 1):C103-11. doi: 10.1152/ajpcell.1996.271.1.C103.


We used the patch-clamp technique to study the effect of extracellular Ca2+ (Ca2+o) on the activity of the apical 70-pS K+ channel in the isolated split-open thick ascending limb (TAL) of the rat kidney. Raising Ca2+o from 1.1 to 5 mM reversibly reduced the activity of the 70-pS K+ channel in cell-attached patches to 16 +/- 2% of the control value within 300 s. In addition, 50 microM neomycin mimicked the effect of an increase in Ca2+o on channel activity in cell-attached patches and completely inhibited channel activity. The effect of neomycin on the channel activity in cell-attached patches is an indirect effect, since addition of 50 microM neomycin on the 70-pS K+ channel in inside-out patches reduced only the apparent amplitude of the channel current without changing channel open probability. We examined further the role of protein kinase C (PKC) and the cytochrome P-450-dependent metabolites of arachidonic acid in mediating the Ca2+o -induced inhibition of channel activity. Addition of phorbol 12-myristate 13-acetate (2 microM) reversibly blocked channel activity in cell-attached patches to 4 +/- 1% of the control value, whereas 75 nM calphostin C increased the channel activity by 115 +/- 10%. Moreover, addition of 1 nM exogenous PKC reversibly and completely inhibited the 70-pS K+ channel. However, inhibition of PKC with calphostin C (75 nM) only slightly prolonged the time course of the effect of Ca2+o on channel activity (370 +/- 40 s) and failed to abolish the inhibitory effect of 5 mM Ca2+o on channel activity in cell-attached patches, indicating that PKC was not mainly responsible for the effect of Ca2+o on channel activity. In contrast, the effect of 5 mM Ca2+o on the apical 70-pS K+ channel was completely abolished when TAL tubules were first incubated in the 17-octadecynoic acid (5 microM)-containing solution, an agent that specifically blocks cytochrome P-450 monooxygenase. In conclusion, these data indicate that Ca2+o is an important regulator of the apical 70-pS K+ channel and that a cytochrome P-450-dependent metabolite of arachidonic acid is involved in mediating this inhibitory effect.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenosine Triphosphate / pharmacology
  • Animals
  • Calcium / pharmacology
  • Calcium / physiology*
  • Cell Membrane / metabolism*
  • Cytochrome P-450 Enzyme System / metabolism*
  • Extracellular Space / metabolism*
  • Fatty Acids, Unsaturated / pharmacology
  • In Vitro Techniques
  • Loop of Henle / metabolism*
  • Neomycin / pharmacology
  • Patch-Clamp Techniques
  • Potassium Channel Blockers*
  • Potassium Channels / drug effects
  • Protein Kinase C / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Tetradecanoylphorbol Acetate / pharmacology


  • Fatty Acids, Unsaturated
  • Potassium Channel Blockers
  • Potassium Channels
  • 17-octadecynoic acid
  • Adenosine Triphosphate
  • Cytochrome P-450 Enzyme System
  • Protein Kinase C
  • Neomycin
  • Tetradecanoylphorbol Acetate
  • Calcium