Figure 4.

Effects of an almost nonstimulating sugar, α-methyl d-mannopyranoside, and GDP-β-S on the currents of outside-out patches. The period of sugar application is shown by a shadowed bar. (A) A current trace when an almost nonstimulating sugar, α-methyl d-mannopyranoside (250 mM) was puff-applied from the stimulation pipette (top) and the control trace when 250 mM sucrose was applied to the same outside-out patch, which might contain <10 sucrose-activated channels (middle). A portion of this trace (where overlapped openings of channels rarely occurred) is shown in an expanded time scale (bottom). The expanded portion is shown by two lines. An estimated full-open level (dotted line with O) of a single-channel current and the basal level (continuous line with C) are shown. Time scales above and below the scale bar are for the top two traces and for the lower expanded trace, respectively. (B) Effect of 1 mM GDP-β-S added to the pseudo-internal solution in the patch pipette on the sucrose-induced current (250 mM) in a different outside-out patch. This current was recorded ∼2 min after formation of the outside-out patch and ∼3 min after establishment of whole-cell clamp.