PT - JOURNAL ARTICLE AU - Mika Fukasawa AU - Hirofumi Nishida AU - Toshiaki Sato AU - Masaru Miyazaki AU - Haruaki Nakaya TI - 6-[4-(1-Cyclohexyl-1<em>H</em>-tetrazol-5-yl)butoxy]-3,4-dihydro-2-(1<em>H</em>)quinolinone (Cilostazol), a Phosphodiesterase Type 3 Inhibitor, Reduces Infarct Size via Activation of Mitochondrial Ca<sup>2+</sup>-Activated K<sup>+</sup> Channels in Rabbit Hearts AID - 10.1124/jpet.108.136218 DP - 2008 Jul 01 TA - Journal of Pharmacology and Experimental Therapeutics PG - 100--104 VI - 326 IP - 1 4099 - http://jpet.aspetjournals.org/content/326/1/100.short 4100 - http://jpet.aspetjournals.org/content/326/1/100.full SO - J Pharmacol Exp Ther2008 Jul 01; 326 AB - 6-[4-(1-Cyclohexyl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-2-(1H)quinolinone (cilostazol), a phosphodiesterase type 3 (PDE III) inhibitor, activates cAMP-dependent protein kinase A (PKA). The cAMP/PKA pathway potentiates the opening of mitochondrial Ca2+-activated K+ (mitoKCa) channels and confers cardioprotection. Although cilostazol has been reported to directly activate sarcolemmal large-conductance Ca2+-activated K+ channels, it remains unclear whether cilostazol modulates the opening of mitoKCa channels. Therefore, we tested the possibility that cilostazol opens mitoKCa channels and protects hearts against ischemia/reperfusion injury. Flavoprotein fluorescence in rabbit ventricular myocytes was measured to assay mitoKCa channel activity. Infarct size in the isolated perfused rabbit hearts subjected to 30-min global ischemia and 120-min reperfusion was determined by triphenyltetrazolium chloride staining. Cilostazol (1, 3, 10, and 30 μM) oxidized flavoprotein in a concentration-dependent manner. The oxidative effect of cilostazol (10 μM) was antagonized by the mitoKCa channel blocker paxilline (2 μM). Activation of PKA by 8-bromoadenosine 3′5′-cyclic monophosphate (0.5 mM) potentiated the cilostazol-induced flavoprotein oxidation. Treatment with cilostazol (10 μM) for 10 min before ischemia significantly reduced the infarct size from 67.2 ± 1.3 (control) to 33.6 ± 5.3% (p &lt; 0.05). This infarct size-limiting effect of cilostazol was abolished by paxilline (60.3 ± 4.9%) but not by the PKA inhibitor (9S,10S,12R)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3′,2′,1′-kl]pyrrolo[3,4-i][1,6]-benzodiazocine-10-carboxylic acid hexyl ester (KT5720) (200 nM, 40.5 ± 3.5%). On the other hand, another PDE III inhibitor, milrinone (10 μM), neither oxidized flavoprotein nor reduced infarct size. Our results suggest that cilostazol exerts a cardioprotective effect via direct activation of mitoKCa channels. The American Society for Pharmacology and Experimental Therapeutics