Thromboxane A2-induced inhibition of voltage-gated K+ channels and pulmonary vasoconstriction -: Role of protein kinase Cζ

Voltage-gated K+ channels (K-V) and thromboxane A(2) (TXA(2)) play critical roles in controlling pulmonary arterial tone under physiological and pathological conditions. We hypothesized that TXA2 might inhibit KV channels, thereby establishing a link between these two major pathogenic pathways in pulmonary hypertension. The TXA2 analogue U46619 inhibited I-K(V) (E-max = 56.1 +/- 3.9%, EC50 = 0.054 +/- 0.019 mumol/L) and depolarized pulmonary artery smooth muscle cells via activation of TP receptors. In isolated pulmonary arteries, U46619 simultaneously increased intracellular Ca2+ concentration and contractile force, and these effects were inhibited by nifedipine or KCl ( 60 mmol/L). U46619-induced contractions were not altered by the inhibitors of tyrosine kinase genistein or Rho kinase Y-27632 but were prevented by the nonselective protein kinase C (PKC) inhibitors staurosporine and calphostin C. Furthermore, these responses were sensitive to Go-6983 but insensitive to bisindolylmaleimide I and Go-6976. Based on the specificity of these drugs, we suggested a role for an atypical PKC in U46619-induced effects. Thus, treatment with a PKCzeta pseudosubstrate inhibitor markedly prevented the vasoconstriction, the inhibition of I-K(V), and the depolarization induced by U46619. Western blots showed a transient translocation of PKCzeta from the cytosolic to the particulate fraction on stimulation with U46619. These results indicate that TXA2 inhibits IK( V), leading to depolarization, activation of L-type Ca2+ channels, and vasoconstriction of rat pulmonary arteries. We propose PKCzeta as a link between TP receptor activation and K-V channel inhibition.