iloprost and iberiotoxin

Activation of a soluble guanylyl cyclase plays an important role in nitric oxide (NO)-induced vasodilation. Recently, we have reported that NO increases the calcium-activated potassium (K(Ca)) channel activity in vascular smooth muscle cells from coronary arteries. The present study examined the role of the soluble guanylyl cyclase in the control of basal activity of the K(Ca) channels and in mediating NO-induced activation of the K(Ca) channels in vascular smooth muscle cells, using a selective inhibitor of this enzyme, 1H-[1,2,4]oxadiazolo[4,2-alpha]quinoxalin-1-one (ODQ). In the cell-attached patch-clamp mode, addition of ODQ into the bath solution (10 micromol/L) decreased the K(Ca) channel activity by 59% and attenuated activation of the channels induced by the NO donor, deta nonoate, by 70%. ODQ had no effect on 8-bromo-cGMP-induced activation of the K(Ca) channels. Deta nonoate produced a concentration-dependent relaxation of precontracted coronary arteries. When ODQ was added to the bath, the deta nonoate-induced relaxations were inhibited. The IC50 for deta nonoate was decreased by about 25-fold and the maximal effect of deta nonoate was reduced by about 60%. A specific K(Ca) channel inhibitor, iberiotoxin, decreased deta nonoate-induced vasodilation but to a lesser extent than ODQ. However, ODQ was without effect on the vasodilation induced by a prostacyclin analog, iloprost, and by adenosine. These results indicate that a soluble guanylyl cyclase and cGMP play an important role in the control of the K(Ca) channel activity in coronary arterial smooth muscle cells. K(Ca) channel activation participates in the NO-induced vasodilation in coronary circulation.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine; Animals; Cattle; Coronary Vessels; Cyclic GMP; Enzyme Inhibitors; Guanylate Cyclase; Iloprost; In Vitro Techniques; Kinetics; Membrane Potentials; Muscle Contraction; Muscle, Smooth, Vascular; Nitroso Compounds; Oxadiazoles; Patch-Clamp Techniques; Peptides; Potassium Channels; Quinoxalines; Scorpion Venoms; Vasodilation

The effect of the stable prostacyclin analog iloprost and its mechanism of action were investigated with the use of pressurized rat tail small arteries with a spontaneous myogenic tone. Iloprost concentration dependently dilated these vessels with a half-maximal effective dose of 5.0 +/- 0.5 x 10(-8) M. Application of 10(-7)-10(-6) M glibenclamide, a blocker of ATP-sensitive potassium (K(ATP)) channels, inhibited the iloprost-induced dilation. Glibenclamide did not affect the basal vessel diameter. The application of 5 x 10(-5)-10(-3) M tetraethylammonium (TEA) and 5 x 10(-9)-10(-7) M iberiotoxin, blockers of calcium-activated potassium (K(Ca)) channels, decreased vessel diameter in the presence of iloprost. Both TEA and iberiotoxin reduced the basal vessel diameter. Glibenclamide at 10(-6) M inhibited the dilation produced by 5 x 10(-5) M Sp-5,6-DCl-cBIMPS, an activator of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase. Iberiotoxin at 10(-7) M decreased vessel diameter in the presence of Sp-5,6-DCl-cBIMPS. H-89 and Rp-8-CPT-cAMPS, blockers of cAMP-dependent protein kinase A (PKA), inhibited the iloprost-induced dilation of these vessels. With use of the whole cell configuration of the patch-clamp technique, it was observed that 5 x 10(-7) M iloprost enhanced an outward current, determined largely by K(Ca) channels, 1.79 +/- 0.17-fold in freshly isolated smooth muscle cells from rat tail small artery. These data show that iloprost dilates rat tail small arteries with a spontaneous myogenic tone and suggest that K(ATP) as well as K(Ca) channels are involved in this effect, which is mediated, at least partly, by PKA.

Topics: Adenosine Triphosphate; Animals; Arteries; Calcium; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Dichlororibofuranosylbenzimidazole; Enzyme Inhibitors; Glyburide; Iloprost; In Vitro Techniques; Kinetics; Male; Muscle, Smooth, Vascular; Peptides; Potassium Channels; Rats; Rats, Inbred WKY; Scorpion Venoms; Tail; Tetraethylammonium; Tetraethylammonium Compounds; Thionucleotides; Vasoconstriction; Vasodilation