Figure 2. Inhibition of M-current in neurons from the rat superior cervical sympathetic ganglion by muscarine (a muscarinic acetylcholine-receptor stimulant).

A, single microelectrode voltage-clamp recording from a dissociated neuron in short-term culture. The cell was held at −35 mV to pre-activate M-current and commanded to −50 mV for 1 s every 10 s to −55 mV to deactivate M-current. Muscarine (10 μm) suppressed outward M-current at the holding potential and eliminated current deactivation tails at −55 mV (see Fig. 1A). (N. V. Marrion & D. A. Brown, unpublished observations; see Marrion et al. 1989 for technical details). B, single microelectrode ‘current-clamp’ recording from a neuron in an intact isolated ganglion. Initial resting potential −53 mV. Muscarine depolarized the neuron, increased input resistance and promoted vigorous repetitive firing during the 1 s current injection, thereby converting the cell from its normal ‘phasic-firing’ discharge pattern to ‘tonic-firing. (Adapted from Brown & Constanti, 1980, with permission.)