Modafinil has been used as a psychostimulant for the treatment of narcolepsy. However, its primary mechanism of action remains elusive. Therefore, we examined the effects of modafinil on K Ca3.1 channels and vascular smooth muscle contraction. K Ca3.1 currents and channel activity were measured using a voltage-clamp technique and inside-out patches in mouse embryonic fibroblast cell line, NIH-3T3 fibroblasts. Intracellular adenosine 3′,5′-cyclic monophosphate (cAMP) concentration was measured, and the phosphorylation of K Ca3.1 channel protein was examined using western blotting in NIH-3T3 fibroblasts and/or primary cultured mouse aortic smooth muscle cells (SMCs). Muscle contractions were recorded from mouse aorta and rat pulmonary artery by using a myograph developed in-house. Modafinil was found to inhibit K Ca3.1 currents in a concentration-dependent manner, and the half-maximal inhibition (IC 50) of modafinil for the current inhibition was 6.8 ± 0.7 nM. The protein kinase A (PKA) activator forskolin also inhibited K Ca3.1 currents. The inhibitory effects of modafinil and forskolin on K Ca3.1 currents were blocked by the PKA inhibitors PKI 14-22 or H-89. In addition, modafinil relaxed blood vessels (mouse aorta and rat pulmonary artery) in a concentration-dependent manner. Modafinil increased cAMP concentrations in NIH-3T3 fibroblasts or primary cultured mouse aortic SMCs and phosphorylated K Ca3.1 channel protein in NIH-3T3 fibroblasts. However, open probability and single-channel current amplitudes of K Ca3.1 channels were not changed by modafinil. From these results, we conclude that modafinil inhibits K Ca3.1 channels and vascular smooth muscle contraction by cAMP-dependent phosphorylation, suggesting that modafinil can be used as a cAMP-dependent K Ca3.1 channel blocker and vasodilator.
- Ca -activated K channel
- Vascular smooth muscle contraction