Effect of the prostacyclin analogue iloprost on K+ permeability in the smooth muscle cells of the canine carotid artery.
The present contribution deals with the electro- and tracerphysiological correlations to vasodilatation observed under prostacyclin or O2 deficiency. Because of the extreme chemical instability of native PGI2, we used iloprost, a stable carbacyclin analogue. At concentrations between 10(-9) and 10(-6) mol/l, iloprost hyperpolarized the resting membrane of normal tone (V = -63.4 mV) and noradrenaline predepolarized vascular smooth muscle cells (V = -55.2 mV) of the canine carotid artery by 7.4 and 16.9 mV, respectively, in a concentration-dependent manner. Correspondingly, the isometric tension was decreased. In both experimental series, the half-maximal effect was attained at a concentration of 2 x 10(-8) mol/l. The coupling ratios developed tension versus membrane potential were 1.079 mV/mN in normal tone and noradrenaline treated preparations. Hyperpolarization and relaxation in the latter group, however, were much larger for the same iloprost concentrations. 42K+ efflux was stimulated by 250% with iloprost (10(-6) mol/l), whereas 24Na+ efflux was increased only by 50%. This resulted in an augmentation of K+ permeability by 340% and of Na+ permeability by 40%, respectively. The ratio PK/PNa rose from 16 to 49 with iloprost. These results lead to the conclusion that iloprost should be classified as a K+ channel opener.
Siegel
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Institute of Physiology, Biophysical Research Group, Free University of Berlin, Germany.
Carl
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Adler
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Stock
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D000818:Animals; D002317:Cardiovascular Agents / Q000494:pharmacology; D002339:Carotid Arteries / Q000187:drug effects / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D004285:Dogs; D004553:Electric Conductivity; D011464:Epoprostenol / Q000494:pharmacology*; D016285:Iloprost; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism
D002317:Cardiovascular Agents; D015221:Potassium Channels; D011464:Epoprostenol; D016285:Iloprost; D011188:Potassium