Endothelin-I and angiotensin II inhibit arterial voltage-gated K+ channels through different protein kinase C isoenzymes.
OBJECTIVE
Voltage-gated K+ (Kv) channels of arterial smooth muscle (ASM) modulate arterial tone and are inhibited by vasoconstrictors through protein kinase C (PKC). We aimed to determine whether endothelin-1 (ET-1) and angiotensin II (AngII), which cause similar inhibition of Kv, use the same signalling pathway and PKC isoenzyme to exert their effects on Kv and to compare the involvement of PKC isoenzymes in contractile responses to these agents.


RESULTS
Kv currents recorded using the patch clamp technique with freshly isolated rat mesenteric ASM cells were inhibited by ET-1 or AngII. Inclusion of a PKCepsilon inhibitor peptide in the intracellular solution substantially reduced inhibition by AngII, but did not affect that by ET-1. Kv inhibition by ET-1 was reduced by the conventional PKC inhibitor Gö 6976 but not by the PKCbeta inhibitor LY333531. Selective peptide inhibitors of PKCalpha and PKCepsilon were linked to a Tat carrier peptide to make them membrane permeable and used to show that inhibition of PKCalpha prevented ET-1 inhibition of Kv current, but did not affect that by AngII. In contrast, inhibition of PKCepsilon prevented Kv inhibition by AngII but not by ET-1. The Tat-linked inhibitor peptides were also used to investigate the involvement of PKCalpha and PKCepsilon in the contractile responses of mesenteric arterial rings, showing that ET-1 contractions were substantially reduced by inhibition of PKCalpha, but unaffected by inhibition of PKCepsilon. AngII contractions were unaffected by inhibition of PKCalpha but substantially reduced by inhibition of PKCepsilon.


CONCLUSIONS
ET-1 inhibits Kv channels of mesenteric ASM through activation of PKCalpha, while AngII does so through PKCepsilon. This implies that ET-1 and AngII target Kv channels of ASM through different pathways of PKC-interacting proteins, so each vasoconstrictor enables its distinct PKC isoenzyme to interact functionally with the Kv channel.
Rainbow
Richard D
RD
Department of Cardiovascular Sciences, University of Leicester, Robert Kilpatrick Clinical Sciences Building, Leicester Royal Infirmary, Leicester LE2 7LX, UK. rdr8@le.ac.uk
Norman
Robert I
RI
Everitt
Diane E
DE
Brignell
Jennifer L
JL
Davies
Noel W
NW
Standen
Nicholas B
NB
D000804:Angiotensin II / Q000378:metabolism*; D000818:Animals; D002463:Cell Membrane Permeability; D019332:Endothelin-1 / Q000378:metabolism*; D015696:Gene Products, tat / Q000378:metabolism; D066298:In Vitro Techniques; D007527:Isoenzymes; D008297:Male; D008638:Mesenteric Arteries / Q000201:enzymology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000201:enzymology*; D009213:Myography; D018408:Patch-Clamp Techniques; D024642:Potassium Channels, Voltage-Gated / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051571:Protein Kinase C-alpha / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051744:Protein Kinase C-epsilon / Q000037:antagonists & inhibitors / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction; D014661:Vasoconstriction / Q000187:drug effects
D019332:Endothelin-1; D015696:Gene Products, tat; D007527:Isoenzymes; D024642:Potassium Channels, Voltage-Gated; D047428:Protein Kinase Inhibitors; D000804:Angiotensin II; C497257:Prkce protein, rat; D051571:Protein Kinase C-alpha; D051744:Protein Kinase C-epsilon