4). These data indicate that the inhibition of Kv-channel currents by (+)MK801 does not depend on the channel activation or inactivation
state. Next, we investigated the steady-state kinetics of Kv channels in the presence and absence of (+)MK801. Steady-state activation of Kv channels was measured using the conventional method by using peak tail currents at −35 mV after various test potentials (upper panel of Fig. 5A). Steady-state inactivation AT13387 ic50 kinetics were also examined using a conventional double-pulse protocol (upper panel of Fig. 5B), which is explained in detail in the Data analysis subsection of the Methods and in the Fig. legend. The results presented in Fig. 1, Fig. 3 and Fig. 4 suggested that (+)MK801 is unlikely to preferentially interact with and modulate the Kv channels in activated or inactivated states in RMASMCs.
In accord, (+)MK801 had little effect on steady-state activation and inactivation kinetics of Kv channels in RMASMCs (Fig. 5A & B). The potential at the half-activation point (V1/2) and the slope value (k) of the steady-state activation curves were −8.6 ± 0.9 and 12.8 ± 0.6 mV for controls, −12.9 ± 1.2 and 10.3 ± 0.7 mV for 100 μM (+)MK801, and −11.9 ± 1.1 and 8.0 ± 0.5 mV for 300 μM (+)MK801, respectively. Furthermore, the V1/2 and k values of the steady-state inactivation curves were −30.7 ± 0.8 and 7.5 ± 0.7 mV for controls, −34.4 ± 1.3 and 8.0 ± 0.8 mV for 100 μM (+)MK801, and −31.5 ± 1.5 and 6.6 ± 1.0 mV for 300 μM (+)MK801, respectively. The time course of the recovery JNJ-26481585 research buy Phosphatidylinositol diacylglycerol-lyase from inactivation of the Kv-channel currents in RMASMCs was also examined in the absence and presence of (+)MK801. The voltage-pulse protocol for measuring the recovery from inactivation is shown in the inset in
Fig. 6A. The recovery time courses in the absence and presence of (+)MK801 were similar: the time constants of the recovery from inactivation of Kv-channel currents in the absence and presence of (+)MK801, which were obtained by data fitting to a single exponential decay curve, were 311 ± 41 and 325 ± 58 ms, respectively. (−)MK801, an optical isomer of (+)MK801, is substantially less effective than (+)MK801 in blocking the NMDAr (9). Thus, we compared the inhibitory effects of (−)MK801 on Kv-channel currents in RMASMCs with the effects produced by (+)MK801. (−)MK801 inhibited Kv-channel currents in a concentration-dependent manner (Fig. 7A). The I–V relationships of the channel currents in the presence and absence of 300 and 1000 μM (−)MK801 are shown in Fig. 7B. Fig. 7C summarizes the concentration-dependent inhibition of Kv-channel currents by (−)MK801. A nonlinear least-squares fit of the Hill equation to the concentration–effect curve of (−)MK801 yielded an IC50 and a Hill coefficient of 134.0 ± 17.5 μM and 0.87 ± 0.09, respectively.