Table 3.

Frequencies of direct transitions between three consecutive open levels

Type of sequence	% (no)	Type of sequence	% (no)
17–42–17	2.98 ± 2.00 (23)	42–33–42	2.94 ± 1.03 (19)
17–42–33	0.00(0)	42–33–49	1.12 ± 0.54(9)
17–42–49	0.00(0)	42–49–33	2.63 ± 1.09(21)
33–42–17	0.33 ± 0.22(2)	42–49–42	6.92 ± 1.04(39)
33–42–33	1.24 ± 0.65(8)	49–33–49	15.35 ± 2.72(86)
33–42–49	1.35 ± 0.46(9)	49–33–42	1.44 ± 0.50(11)
33–49–33	1.13 ± 0.75(8)	49–42–17	0.19 ± 0.13(2)
33–49–42	1.93 ± 0.69(15)	49–42–33	2.04 ± 1.82(3)
42–17–42	7.76 ± 3.91(64)	49–42–49	5.63 ± 6.34(309)

The percentage of all direct transitions (shown as means ± s.e.m.) involving three consecutive current levels is given (with the total number of each transition sequence) for six patches where both high and low conductance channels were evident. Direct transitions between open current levels were identified as events where both open levels were greater than 2.5T_r = 415 μs in duration and no gap longer than the shut time resolution (50 μs) was detected between the two levels. Openings were allocated to each of the four different conductance levels using A_crit values calculated from the amplitude distribution as described in Methods. Of the 36 possible ways four different open channel current levels can be connected in sequences of three, only 18 sequences are presented. All other sequences involved direct transitions between 17 and 33 pS levels or between 17 and 49 pS levels which had already been found not to occur (Table 2 and Fig. 6).