Fig. 5.

Single channels resulting from α + β2 coexpression reveal that individual channels can contain less than four β2 subunits per channel. A–D, Traces from four different patches are illustrated. In each panel, thetop three traces show records of single-channel openings, whereas the bottom trace shows the ensemble current average. Channel openings were activated by a voltage-step to +100 mV with 10 μm Ca²⁺.A, The resulting ensemble current average exhibited a τ_i of 21.8 msec; B, τ_i= 33.6 msec; C, τ_i = 54.3 msec;D, τ_i = 97.9 msec. Note the differences in the single-channel current amplitude in each case measured at +100 mV. The tendency toward a larger single-channel conductance with fewer numbers of β subunits was consistently observed. There is also a tendency for channels to exhibit more frequent brief closures per unit of open time as the number of β2 subunits per channel is reduced. For each single channel trace, thedashed lines indicate the open current level (top) and closed current level (bottom). For current averages, the dashed lines indicate P(0) levels of 1.0 (top) and 0.0, respectively.