FIGURE 4.

Single channel trace recorded from an inside-out patch treated with PKA-cs and 100 nM G_β1/γ2. (A, top) 200 s of history in the lifetime of a single GIRK1/GIRK4 channel, phosphorylated by PKA-cs and activated by G_β1/γ2. (A, lower traces) Segments of the current trace shown on the top of A, expanded at increasing timescales, to demonstrate the multiplicity of channel closed time distributions over several orders of magnitude in durations. At the most expanded timescale, short and longer lived openings also can be seen. (B, left) Probability density function (p.d.f.) of open time distribution for the current trace shown in A. +, experimental data; (solid line), maximum likelihood regression obtained by fitting the data to the sum of two exponentials. (B, right) The p.d.f. of closed time distributions. Data were fitted by the sum of five exponentials.