Identification of M-channels in outside-out patches excised from sympathetic ganglion cells.

We have identified the species of K+ channel that underlies the neuronal M-current in rat sympathetic ganglion cells. The channels were kinetically and pharmacologically defined using outside-out and cell-attached patches. They exhibited multiple conductance levels, predominantly 3-9 pS. Their slow gating in response to voltage change in outside-out patches was exhibited only in the presence of AIF-4 or GTP gamma S on the inner membrane surface and when the lower conductance states were dominant. In the absence of AIF-4 or GTP gamma S, the channels exhibited rapid activation and deactivation. We conclude that M-channel gating may be controlled by an associated GTP-binding protein.