cGMP signals mainly through cAMP kinase in permeabilized murine aorta.
GMP affects vascular tone by multiple mechanisms, including inhibition of the Rho/Rho kinase-mediated Ca(2+) sensitization, a process identified as Ca(2+) desensitization. Ca(2+) desensitization is mediated probably by both cGMP- and cAMP-dependent protein kinases (cGKI and PKA). We investigate to which extent Ca(2+) desensitization is initiated by cGKI and PKA. cGMP/cAMP-induced relaxation was studied at constant [Ca(2+)] in permeabilized aortas from wild-type and cGKI-deficient mice. [Ca(2+)] increased aortic tone in the absence and presence of 50 microM GTPgammaS with EC(50) values of 160 and 30 nM, respectively. In the absence of GTPgammaS, the EC(50) for [Ca(2+)] was shifted rightward from 0.16 microM to 0.43 and 0.82 microM by 1 and 300 microM 8-bromo-cGMP (8-Br-cGMP), and to 8 microM by 10 microM Y-27632. Contractions induced by 300 nM [Ca(2+)] were relaxed by 8-Br-cGMP with an EC(50) of 2.6 microM. Surprisingly, [Ca(2+)]-induced contractions were also relaxed by 8-Br-cGMP in aortas from cGKI(-/-) mice (EC(50) of 19 microM). Western blot analysis of the vasodilator-stimulated phosphoprotein indicated "cross"-activation of PKA by 1 mM 8-Br-cGMP in aortic smooth muscle cells from cGKI(-/-) mice. Indeed, the PKA inhibitor peptide (PKI 5-24) completely abolished the relaxant effect of 8-Br-cGMP in muscles from cGKI(-/-) mice and to 65% in wild-type aortas. The thromboxane analogue U-46619 induced contraction at constant [Ca(2+)], which was only partially relaxed by 8-Br-cGMP but completely relaxed by Y-27632. The effect of 8-Br-cGMP on U-46619-induced contraction was attenuated by PKI 5-24. These results show that cGKI has only a small inhibitory effect on Ca(2+) sensitization in murine aortas.
Wörner
René
R
Institut für Pharmakologie und Toxikologie, Technische Universität München, Biedersteiner Str. 29, 80802 München, Germany.
Lukowski
Robert
R
Hofmann
Franz
F
Wegener
Jörg W
JW
D000818:Animals; D001013:Aorta, Thoracic / Q000502:physiology*; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009119:Muscle Contraction / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology*
D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D006152:Cyclic GMP