Table 1.
Comparison of Boltzmann parameters of intercellular channels composed of either Cx32wt or functional CMTX mutations expressed in paired Xenopus oocytes
| Cx (condition)1-a | A | n | V0(mV) | Gjmin |
|---|---|---|---|---|
| Homotypic | ||||
| Cx32wt (+Vj) | 0.12 | 3.0 | 61 | 0.38 |
| Cx32wt (−Vj) | 0.11 | 2.7 | 59 | 0.27 |
| L56F (+Vj) | 0.09 | 2.4 | 47 | 0.24 |
| L56F (−Vj) | 0.11 | 2.7 | 48 | 0.32 |
| E102G | 0.11 | 2.7 | 58 | 0.20 |
| Del111–116 | 0.12 | 3.0 | 40 | 0.11 |
| R220stop | 0.13 | 3.2 | 47 | 0.26 |
| Heterotypic1-1002 | ||||
| L56F/Cx32wt (+Vj) | 0.10 | 2.5 | 62 | 0.24 |
| L56F/Cx32wt (−Vj) | 0.13 | 3.2 | 52 | 0.23 |
| E102G/Cx32wt (+Vj) | 0.12 | 3.0 | 54 | 0.15 |
| E102G/Cx32wt (−Vj) | 0.12 | 3.0 | 55 | 0.27 |
| Del111–116/Cx32wt (+Vj) | 0.13 | 3.2 | 37 | 0.10 |
| R220stop/Cx32wt (+Vj) | 0.14 | 3.5 | 43 | 0.25 |
| R220stop/Cx32wt (−Vj) | 0.12 | 3.0 | 54 | 0.27 |
Junctional conductance (Gj) developed between pairs of Xenopus oocytes expressing different constructs was measured by dual voltage clamp in response to increasing transjunctional potentials (Vj) of opposite polarity, as described in Materials and Methods. The same pairs presented in Figures 4 and 6 were used to calculate the parameters derived from the best fits to the Boltzmann equation given in Materials and Methods. Gjmin is the normalized conductance at the largest Vj (±80 mV), andV0 is the voltage at which half-maximal decrease of Gj occurs. The cooperativity constantA, a parameter reflecting the slope of the curve, also can be expressed as the gating charge n, where n= A(kT/q) with k = Boltzmann constant,T = absolute temperature, and q = elementary charge.
The plus and minus signs forVj refer to the polarity of the transjunctional potential. When not indicated, the response was symmetrical.
F1-1002: In all cases the cell expressing Cx32wt was either depolarized or hyperpolarized, whereas the other oocyte, expressing the CMTX mutation, was held at a constant voltage. Thus, positive Vj denotes that the wild-type injected oocyte is relatively positive, whereas negativeVj denotes that the cell expressing the CMTX mutation is relatively positive. The voltage-induced channel closure of the Del111–116 side could not be fit by a Boltzmann equation.