Lastly, we examined the effects of (+)MK801 on the Em of RMASMCs. Because Kv-channel currents are the dominant regulators of resting Em in RMASMCs (28), MK801 treatment was expected to depolarize the Em of RMASMCs. Applying (+)MK801 induced rapid and reversible depolarization of Em in a concentration-dependent manner (Fig. 8A). Fig. 8B presents the resting

Em values in the absence and presence of various concentrations of (+)MK801, and Fig. 8C summarizes the concentration-dependent depolarizing effects. To confirm GDC-0449 ic50 that (+)MK801-induced Em depolarization was because of the inhibition of K+ channels, we measured the Gm by repetitively injecting brief hyperpolarizing current pulses (amplitude −20 pA, duration 1 s, interval 15–35 s), which are reflected as transient

negative deflections (hyperpolarizations) of Em (Fig. 8A). Gm was calculated from Ohm’s law as follows: G = I/V,where I is the amplitude of the injecting current (−20 pA here) and V is the amplitude of the transient Em hyperpolarization resulting from current injection. The tracing of Em in Fig. 8A indicates that the (+)MK801-induced Em depolarization is associated mainly with the inhibition of K+ conductance, and not with the activation of a depolarizing conductance. Fig. 8D summarizes the concentration-dependent decrease in Gm caused by (+)MK801. The results of the present study indicate that MK801 blocks Kv channels independently of NMDAr and CDK inhibitor that this inhibition may depolarize the Em of vascular smooth muscle under clinical settings. To the best of our knowledge, this is the first study to demonstrate that MK801 blocks Kv channels and depolarizes Em in vascular smooth muscle cells. This MK801 inhibition of Kv channels, in addition to the NMDAr block, should be considered when assessing the various pharmacological effects of MK801 such as hypertension as well as schizophrenia. Ketamine, which is another PCP-derivative, is similar to MK801 in structure and pharmacological action and is an effective anesthetic, especially in patients at risk of hypotension during anesthesia: unlike other anesthetics, all ketamine increases

blood pressure (29). Although the hypertensive effect of ketamine is generally considered the result of inhibition of central and peripheral catecholamine reuptake (30) and (31) and direct stimulation of the CNS, the exact mechanism involved remains unclear. Inhibition of BKCa and Kv channels in vascular smooth muscle has been suggested as another mechanism of ketamine-induced hypertension (14) and (32). Moreover, no study has yet examined whether or not the inhibition of central and peripheral catecholamine reuptake and direct stimulation of the CNS (30) and (31) involves Kv-channel inhibition. MK801 is not administered clinically because of its critical side effect such as the neurotoxic effects called Olney’s lesions (33) and (34).