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 t
2. Rp-cAMPS, an inhibitor of PKA, did not affect K-ATP currents activated b
y 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 curr
3. Ang II (100 nM) inhibited K-ATP current activated by the K+ channel open
er 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) rec
eptor antagonist losartan.
4. The inhibition of K-ATP currents by Ang II was abolished by a, combinati
on of PKA inhibitor peptide 5-24 (5 muM) and PKC inhibitor peptide 19-27 (1
00 muM), while either alone caused only partial block of the effect.
5. In the presence of PKA inhibitor peptide, the inhibitory effect of Ang I
I was unaffected by the PKC inhibitor Go 6976, which is selective for Ca2+-
dependent isoforms of PKC, but was abolished by a selective peptide inhibit
or of the translocation of the epsilon isoform of PKC.
6. Our results indicate that K-ATP channels are activated by steady-state p
hosphorylation by PKA at normal intracellular ATP levels, and that Ang II i
nhibits the channels both through activation of PKC epsilon and inhibition