Table 1.

Open and closed time constants of human and murine CFTR Cl⁻ channels

					Area under curve
	τo (ms)	τcf (ms)	τci (ms)	τcs (ms)	τcf	τci	τcs	n
Human	66.8 ± 8.59	3.18 ± 0.20	—	169.4 ± 26.7	0.59 ± 0.02	—	0.41 ± 0.02	6
Murine	6.22 ± 0.83	5.27 ± 0.76	84.0 ± 6.47	410.1 ± 42.4	0.51 ± 0.03	0.43 ± 0.04	0.06 ± 0.01	6

Time constants were derived from the fitting of one-, two- or three-component exponential functions to open and closed time histograms using the maximum likelihood method as described in the Methods. τ_o, open time constant; τ_cf, fast closed time constant; τ_ci, intermediate closed time constant; τ_cs, slow closed time constant. Area under curve indicates the proportion of the total closed time distribution that corresponds to the different closed time constants. Measurements were made in the presence of ATP (1 mM) and PKA (75 nM) at −50 mV. Data are means ±s.e.m. of n single-channel patches and in each patch approximately 5000 events were analysed. Although the number of events in the closed time histograms were relatively small (1000 to 3000), for murine CFTR six of six closed time histograms were fitted with a three-component exponential and all six fits were significant both by the F statistic (P < 0.05) and the LLR test (> 2). In contrast, for human CFTR only two of six closed time histograms could be fitted with a three-component exponential and of these only one fit was significant by both the F statistic (P < 0.05) and the LLR test (> 2). For murine CFTR, similar results were obtained when the number of closed time events was greater than 7600.