Mechanisms of vasodilation induced by NKH477, a water-soluble forskolin derivative, in smooth muscle of the porcine coronary artery.
To study the mechanism of vasodilation induced by 6-(3-dimethylaminopropionyl) forskolin (NKH477), a water-soluble forskolin derivative, its effects on the acetylcholine (ACh)-induced contraction of muscle strips of porcine coronary artery were examined. [Ca2+]i, isometric force, and cellular concentrations of cAMP and inositol 1,4,5-trisphosphate were measured. NKH477 (0.1-1.0 microM), isoproterenol (0.01-0.1 microM), or forskolin (0.1-1.0 microM) increased cAMP and attenuated the contraction induced by 128 mM K+ or 10 microM ACh in a concentration-dependent manner. These agents, at concentrations up to 0.3 microM, did not change the amount of cGMP. NKH477 (0.1 microM) attenuated the contraction induced by 128 mM K+ without corresponding changes in the evoked [Ca2+]i responses. ACh (10 microM) produced a large phasic increase followed by a small tonic increase in [Ca2+]i and produced a sustained contraction. The ACh-induced phasic increase in [Ca2+]i, but not the tonic increase, disappeared after application of 0.1 microM ionomycin. NKH477 (0.1 microM) attenuated both the increase in [Ca2+]i and the force induced by 10 microM ACh in muscle strips that were not treated with ionomycin and inhibited the ACh-induced contraction without corresponding changes in [Ca2+]i in ionomycin-treated muscle strips. These results suggest that NKH477 inhibits ACh-induced Ca2+ mobilization through its action on ionomycin-sensitive storage sites. In ionomycin-treated and 128 mM K(+)-treated muscle strips, 0.1 microM NKH477 shifted the [Ca2+]i-force relation to the right in the presence or absence of 10 microM ACh. In beta-escin-skinned smooth muscle strips, 0.1 microM NKH477 shifted the pCa-force relation to the right but had no effects on Ca(2+)-independent contraction. We conclude that in smooth muscle of porcine coronary artery, NKH477 inhibits ACh-induced contraction by both attenuating ACh-induced Ca2+ mobilization and reducing the sensitivity of the contractile machinery to Ca2+, possibly by activating cAMP-dependent mechanisms.
Shafiq
J
J
Department of Pharmacology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Suzuki
S
S
Itoh
T
T
Kuriyama
H
H
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001158:Arteries; D005576:Colforsin / Q000031:analogs & derivatives* / Q000494:pharmacology; D003331:Coronary Vessels / Q000187:drug effects* / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D015759:Ionomycin / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D012995:Solubility; D013552:Swine; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation / Q000502:physiology*; D014867:Water
D014867:Water; D005576:Colforsin; D015759:Ionomycin; D015544:Inositol 1,4,5-Trisphosphate; D000242:Cyclic AMP; D007545:Isoproterenol; D000109:Acetylcholine; D011188:Potassium