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Eur J Cardiothorac Surg 2006;30:329-332
© 2006 Elsevier Science NL

The role of potassium channels in the vasodilatory effect of levosimendan in human internal thoracic arteries

^a Department of Pharmacology, Akdeniz University, Medical Faculty, 07070 Antalya, Turkey
^b Department of Cardiovascular Surgery, Akdeniz University, Medical Faculty, Antalya, Turkey
^c Department of Anaesthesiology, Akdeniz University, Medical Faculty, Antalya, Turkey

Received 19 January 2006; received in revised form 15 May 2006; accepted 17 May 2006.

^_* Corresponding author. Tel.: +90 242 227 43 43x44163; fax: +90 242 247 44 82. (Email: sozdem{at}akdeniz.edu.tr).

Objective: We investigated the role of potassium channels in vasodilatory effect of levosimendan in human internal thoracic arteries. Methods: Samples of redundant internal thoracic arteries obtained from patients undergoing a coronary artery bypass graft surgery were cut into 3 mm wide rings and suspended in 20 ml organ baths. Isometric tension was continuously measured with an isometric force transducer connected to a computer-based data acquisition system. Results: Levosimendan (10^–8–10^–5 M) or cromakalim (10^–8–10^–5 M) produced concentration-dependent relaxation responses in human internal thoracic arteries precontracted by 10^–6 M phenylephrine. The relaxant responses to levosimendan did not differ significantly between endothelium-intact and endothelium-denuded preparations. Incubation of human internal thoracic artery rings with adenosine 3',5'-triphosphate (ATP)-dependent potassium channel blocker glibenclamide (10^–6 M) for 30 min significantly inhibited the relaxant responses to both levosimendan and cromakalim. The Ca²⁺-activated potassium channel blocker iberiotoxin (10^–7 M) also caused a significant but smaller inhibition on relaxant responses to levosimendan. Incubation of the rings with the voltage-dependent potassium channel blocker 4-aminopyridine (5 mM) for 10 min did not cause significant alterations in relaxant responses to levosimendan. Conclusions: The findings of this study suggested that levosimendan-induced relaxation responses in human internal thoracic arteries were depended on the activation of ATP-dependent and Ca²⁺-activated potassium channels.

Key Words: Levosimendan • Potassium channel • Human internal thoracic artery • Vasodilatation

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