Figure 2.

The prevalent, depolarization-activated channel in cell-attached recording is a K⁺ channel. One-second-long voltage ramp (from a hyperpolarizing −100 mV to depolarizing 40 mV) was applied repetitively at 10-s intervals to a membrane patch of a flexor protoplast. To increase the chance of K_D-channel opening during the ramps, a 20-mV depolarization was applied between the ramps, and the ramps were fast (i.e. the gating was not at steady state). A, Three superimposed traces of unitary currents during the voltage ramps in an on-cell (onc) configuration. Straight lines indicate the idealized (eye-fitted) currents through single open channels. Arrows indicate a reversal potential of −76 mV, determined by linear fitting of the lower or the upper parts of the traces (a or b, solid or dashed lines, respectively). Numbers at the right indicate the number of channels open simultaneously (the all-channels-closed level was observed in other records, not shown). The unitary conductance increased between levels 1 and 3 in steps of 15 pS on average. B, Two superimposed traces of currents from the same membrane patch within 3 min after excision into an inside-out (i-o) configuration. Open channel conductance (between levels 1 and 2), 17 pS; arrow c, reversal potential of −76 mV; arrow d, opening of a third channel; arrow e, a small, unidentified channel seen occasionally at higher depolarizations. Scale bars are common to A and B.