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

1. We used whole-cell patch clamp to investigate steady-state activation of ATP-sensitive K+ channels (K-ATP) of rat arterial smooth muscle by protein kinase A (PKA) and the pathway by which angiotensin II (Ang II) inhibits these channels. 2. Rp-cAMPS, an inhibitor of PKA, did not affect K-ATP 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 K-ATP current, while the phosphatase inhibitor calyculin A caused a small increase in current. 3. Ang II (100 nM) inhibited K-ATP 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 AT(1) receptor antagonist losartan. 4. The inhibition of K-ATP currents by Ang II was abolished by a, combination of PKA inhibitor peptide 5-24 (5 muM) and PKC inhibitor peptide 19-27 (100 muM), while either alone caused only partial block of the effect. 5. In the presence of PKA inhibitor peptide, the inhibitory effect of Ang II was unaffected by the PKC inhibitor Go 6976, which is selective for Ca2+-dependent isoforms of PKC, but was abolished by a selective peptide inhibitor of the translocation of the epsilon isoform of PKC. 6. Our results indicate that K-ATP 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 PKC epsilon and inhibition of PKA.