Potassium channels in the vasodilating action of levosimendan on the human umbilical artery.

Objective: Levosimendan is a calcium-sensitizing agent and inodilator working via potassium channels, which is under current investigation in the treatment of heart failure. We investigated the type of potassium channels that play a role on the dilatating effect of levosimendan on the contractile tones of the isolated human umbilical artery (HUA).

Methods: The response in the HUA was recorded isometrically by a force displacement transducer in isolated organ baths. Levosimendan was added to organ baths after precontraction with serotonin (5-HT, 1 microM). Levosimendan-induced relaxations were tested in the presence of the large conductance Ca2+-activated K+ channel inhibitor tetraethylammonium (TEA, 1 mM), the adenosine triphosphate (ATP)-sensitive K+ channel inhibitor glibenclamide (GLI, 10 microM), and the voltage-sensitive K+ channel inhibitor 4-aminopyridine (4-AP, 1 mM). All experiments were performed in solutions containing the cyclooxygenase inhibitor indomethacin (10 microM) and the nitric oxide synthase inhibitor L-NAME (100 microM).

Results: Levosimendan (10 nM to 3 microM) produced potent relaxation in the HUA. Vehicle had no significant relaxant effect. The relaxation to levosimendan was not affected by the K+ channel inhibitor, GLI. However, 4-AP (1 mM) and TEA (1 mM) inhibited levosimendan-induced relaxation significantly (P <.05).

Conclusion: These results show that levosimendan effectively and directly decreases the tone of the HUA. The mechanism of this levosimendan-induced relaxation in the HUA appears in part to be due to voltage-gated and large conductance Ca2+-activated K+ channel opening action.