XB-IMG-122111
Xenbase Image ID: 122111
![]() |
Figure 9. . High affinity block of W434F channels by barium in Na+ and Tris+ solutions. (A) Micromolar concentration of barium blocks W434F channels in K+-free solutions. Depolarizing steps of 20 ms duration to 60 mV were applied every second from a holding potential of â100 mV. Currents were recorded from an outside-out patch containing W434F channels. The external solution contained (in mM) 36 Na+ + 79 Tris+, and the internal solution was 115 Na+, yielding a reversal potential of about â30 mV. Switching to an external solution containing 1 μM Ba2+ resulted in an almost complete block of both the outward current and the inward tail current in five pulses. (B) Inward dissociation of Ba2+ is slow in a Tris+ internal solution. Recordings are from an outside-out patch containing W434F channels. The pipette solution (internal solution) contained 115 Tris+. The external solution originally was 115 Na+. A step pulse to 0 mV for 15 ms followed by a return to â100 mV evoked a small inward Na+ current followed by a large Na+ tail current (trace 1). The external solution was then switched to 115 Tris+ + 2 Ba2+, which abolished all ionic currents, leaving only the gating currents (trace 2). After switching back to 115 Na+ again, the first trace recorded 8 s after the switch showed very little tail current (trace 3), indicating that most of the channels were still blocked by Ba2+. Further washing resulted in the full recovery of the Na+ current (trace 4) with a time constant of 38 s. Image published in: Varga Z et al. (2002) Copyright © 2002, The Rockefeller University Press. Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View |