title: Essential role of mitochondrial Ca2+-activated and ATP-sensitive K+ channels in sildenafil-induced late cardioprotection.
abstract: Sildenafil (Viagra), a phosphodiesterase type-5 inhibitor used in treatment of male erectile dysfunction and pulmonary hypertension can induce cardioprotection through opening of mitochondrial ATP-sensitive K(+) channels (mitoK(ATP)). Recent studies suggest that activation of mitochondrial Ca(2+)-activated K(+) channels (mitoK(Ca)) also has anti-ischemic effects. However, the relative role of mitoK(Ca) and mitoK(ATP) in sildenafil-induced cardioprotection remains unknown. In the present study, adult male ICR mice were pretreated with sildenafil (0.71 mg/kg, i.p.) 24 h prior to 20 min of global ischemia followed by 30 min of reperfusion in Langendorff mode. Paxilline (blocker of K(Ca)) or 5-hydroxydecanoic acid (5-HD; blocker of mitoK(ATP)) was administered either 30 min before sildenafil or 10 min prior to ischemia. Treatment with sildenafil reduced infarct size, which was abolished by either paxilline or 5-HD. Furthermore, in vivo gene knockdown of beta1 subunit of K(Ca) (K(Ca)-beta1) using small interfering RNA (siRNA) administered 48 h before sildenafil injection blocked the infarct limiting effect of sildenafil. The protective effect of sildenafil was preserved in mice treated with non-target siRNA. Western blots demonstrated selective protein expression of K(Ca)-beta1 in cardiac mitochondria and the gene knockdown effect of siRNA on K(Ca)-beta1. The level of K(Ca)-beta1 protein was not upregulated following treatment with sildenafil. We conclude that both mitoK(Ca) and mitoK(ATP) play a critical role in triggering and mediating sildenafil-induced delayed cardioprotection. The results suggest that activation of mitoK(Ca) and mitoK(ATP) are crucial for maintaining mitochondrial homeostasis and reducing cell death in sildenafil-induced preconditioning against ischemia-reperfusion injury.
authors.affiliation: Division of Cardiology, Department of Internal Medicine, Box 980204, Virginia Commonwealth University, 1101 East Mashall Street, Room 7-046, Richmond, VA 23298-0204, USA.
authors.forename: Xiaoyin
authors.initials: X
authors.lastname: Wang
authors.forename: Patrick W
authors.initials: PW
authors.lastname: Fisher
authors.forename: Lei
authors.initials: L
authors.lastname: Xi
authors.forename: Rakesh C
authors.initials: RC
authors.lastname: Kukreja
mesh_terms: D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology*; D003326:Coronary Circulation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D006334:Heart Function Tests; D006352:Heart Ventricles / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D008929:Mitochondria, Heart / Q000187:drug effects* / Q000378:metabolism*; D009200:Myocardial Contraction / Q000187:drug effects; D015428:Myocardial Reperfusion Injury; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D010879:Piperazines / Q000494:pharmacology*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated / Q000235:genetics / Q000378:metabolism*; D011687:Purines / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D020127:Recovery of Function / Q000187:drug effects; D000068677:Sildenafil Citrate; D013450:Sulfones / Q000494:pharmacology*; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D002316:Cardiotonic Agents; D010879:Piperazines; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D011687:Purines; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D013450:Sulfones; D014665:Vasodilator Agents; C117780:mitochondrial K(ATP) channel; D000068677:Sildenafil Citrate