Angiotensin II inhibits rat arterial KATP channels by inhibiting steady-state protein kinase A activity and activating protein kinase Ce

Authors


Corresponding author: Ion Channel Group, Department of Cell Physiology and Pharmacology, University of Leicester, PO Box 138, Leicester LE1 9HN, UK. Email: nbs@le.ac.uk

Abstract

  • 1We used whole-cell patch clamp to investigate steady-state activation of ATP-sensitive K+ channels (KATP) of rat arterial smooth muscle by protein kinase A (PKA) and the pathway by which angiotensin II (Ang II) inhibits these channels.
  • 2Rp-cAMPS, an inhibitor of PKA, did not affect KATP currents activated by pinacidil when the intracellular solution contained 0.1 mM ATP. However, when ATP was increased to 1.0 mM, inhibition of PKA reduced KATP current, while the phosphatase inhibitor calyculin A caused a small increase in current.
  • 3Ang II (100 nM) inhibited KATP current activated by the K+ channel opener pinacidil. The degree of inhibition was greater with 1.0 mM than with 0.1 mM intracellular ATP. The effect of Ang II was abolished by the AT1 receptor antagonist losartan.
  • 4The inhibition of KATP currents by Ang II was abolished by a combination of PKA inhibitor peptide 5-24 (5 μM) and PKC inhibitor peptide 19-27 (100 μM), while either alone caused only partial block of the effect.
  • 5In the presence of PKA inhibitor peptide, the inhibitory effect of Ang II was unaffected by the PKC inhibitor Gö 6976, which is selective for Ca2+-dependent isoforms of PKC, but was abolished by a selective peptide inhibitor of the translocation of the ε isoform of PKC.
  • 6Our results indicate that KATP channels are activated by steady-state phosphorylation by PKA at normal intracellular ATP levels, and that Ang II inhibits the channels both through activation of PKCε and inhibition of PKA.

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