The currents were elicited using 50-ms-long depolarizing voltage step pulses to between −20 mV and +50 mV from the holding potential of −70 mV (Fig. 2A). As shown by the control trace in Fig. 2A, Selleckchem PF2341066 the activation time constant became smaller as depolarization became stronger. (+)MK801 had little effect on the activation time

course of the Kv-channel currents. The activation time constants for voltage steps from −20 mV to +50 mV in the presence and absence of (+)MK801 are presented in Fig. 2B. Next, we examined the effects of (+)MK801 on the inactivation time course of Kv-channel currents; the inactivation was slow, and time course of inactivation was examined during 10-s-long voltage steps to +40 mV from the holding potential of −70 mV (Fig. 2C). The traces in Fig. 2C shows representative inactivation time courses in the presence and absence of (+)MK801. (+)MK801 substantially accelerated the slow inactivation time course of Kv-channel currents in a concentration-dependent manner (Fig. 2C & D). We examined whether (+)MK801 inhibited Kv-channel currents in RMASMCs in a use-dependent manner. We applied 20 repetitive 125-ms depolarizing step pulses to +40 mV from a holding potential of −70 mV at two frequencies,

1 and 2 Hz. Use dependence was tested after (+)MK801 had steadily inhibited the currents. Fig. 3A shows representative, superimposed current traces under control conditions and in the presence of 300 μM (+)MK801. The results are summarized in Fig. 3B. The Kv-channel current amplitude decreased progressively DAPT nmr during 4-Aminobutyrate aminotransferase the repetitive depolarizing pulses. The progressive decrease in peak current amplitude was slightly more dominant in the presence of 100 and 300 μM (+)MK801 (Fig. 3B). The trains of repetitive voltage steps are frequently used to examine the use and/or state dependency of ion channel blockage. Although the data shown in Fig. 3 suggest partial use-dependent inhibition of Kv-channel currents by

(+)MK801, the disparity in the progressive decrease of currents in the absence and presence of (+)MK801 was extremely small. Moreover, the slow inactivation of the Kv-channel current shown in Fig. 2 may be reflected cumulatively during the 20 repetitive 125-ms depolarizing step pulses. To address the above possibility, we examined the inhibition by the first depolarizing voltage steps after (+)MK801 treatment and compared it with the steady-state inhibition. Because a small fraction of the channels may have been spontaneously active or inactive at the holding potential of −70 mV and (+)MK801 might have bound these channels, we clamped the RMASMCs at −110 mV before and during (+)MK801 application without the depolarizing voltage steps (Fig. 4).