Table I.
Activation Parameters for Eag and Mutant Constructs
| Construct | Vmid | A | Vrest | |||
|---|---|---|---|---|---|---|
| mV | mV | mV | ||||
| Eag | −4.3 ± 0.6(8) | 12.7 ± 0.5(8) | −44.9 ± 11.1(16) | |||
| S4-1 chimera | +84.6 ± 0.7(6) | 19.9 ± 0.6(6) | — | |||
| S4-2 chimera | +68.5 ± 0.6(6) | 26.7 ± 0.5(6) | — | |||
| S3+loop chimera | ND | ND | −78.2 ± 8.8*(20) | |||
| Loop chimera | ND | ND | −74.2 ± 9.0*(14) | |||
| A345E | −51.9 ± 0.4(7) | 14.4 ± 0.4(7) | −82.1 ± 10.9*(10) | |||
| A345R | ND | ND | −69.7 ± 6.3*(7) | |||
| L342H | +16.3 ± 0.6(4) | 15.5 ± 0.5(4) | −38.3 ± 14.2(12) | |||
| Δ333-337 | +11.4 ± 0.6(6) | 12.8 ± 0.6(6) | −39.5 ± 5.8(15) | |||
| I317K | +3.7 ± 1.2(7) | 17.6 ± 1.0(7) | −37.3 ± 7.0(10) |
Values for the midpoint potential (Vmid) and the slope factor (A) (in mV, mean ± SEM) were derived from P
O-V curves fit with a Boltzmann equation of the form: 
, where P
O is the fraction of open channels obtained from the normalized amplitude of isochronal tail currents after a depolarization to the test potential (V). Activation curves for the S4-1 and S4-2 chimeras did not saturate within the tested voltage range (see Fig. 2
C), leading to inaccurate values for Vmid and A for these mutants. Values for Vmid and A were not determined (ND) for the S3+loop and loop chimeras, and the A345R mutation, which shifted activation far in the hyperpolarized direction. Also shown is the resting membrane potential (Vrest, mean ± SD) in 1 mM KC1 for oocytes expressing each construct. Vrest values marked with
are significantly different from the wild-type eag control (t test, P < 0.01). The number of experiments, n, is given in parentheses.