Figure 1. Basic properties of M-current as recorded in frog sympathetic neurons.

Twin-microelectrode recording from two different neurons. V, voltage; I, current. A, with a step-depolarization under voltage clamp, the current is seen as a slowly activated (τ≈ 150 ms) non-inactivating outward current with a threshold around −60 mV and half-activation at around −35 mV (from Adams et al. 1982). B, under current clamp the M-current acts as the neuron's own in-built ‘voltage clamp’. Thus, a ±0.2 nA current injection at −90 mV (where M-channels are shut) produces large (∼30 mV) voltage responses. In contrast, at −46 mV, where M-current is partly activated, the same current injections produce an initial transient voltage excursion, but the subsequent opening or closing of M-channels restores the membrane potential resulting in very little (< 5 mV) steady-state voltage change (from Brown, 1988). Figure adapted from Delmas & Brown (2005), with permission.