The CO2 sensitivity of transjunctional voltage (V j) gating was studied by dual voltage clamp in oocytes expressing mouse Cx40 or its COOH terminus (CT)-truncated mutant (Cx40-TR). V j sensitivity, determined by a standard V j protocol (20 mV V j steps, 120 mV maximal), decreased significantly with exposure to 30% CO2. The Boltzmann values of control versus CO2-treated oocytes were: V 0 = 36.3 and 48.7 mV, n = 5.4 and 3.7, and G j min = 0.21 and 0.31, respectively. CO2 also affected the kinetics of V j-dependent inactivation of junctional current (I j); the time constants of two-term exponential I j decay, measured at V j = 60 mV, increased significantly with CO2 application. Similar results were obtained with Cx40-TR, suggesting that CT does not play a role in this phenomenon. The sensitivity of Cx40 channels to 100% CO2 was also unaffected by CT truncation. There is evidence that CO2 decreases the V j sensitivity of Cx26, Cx50 and Cx37 as well, whereas it increases that of Cx45 and Cx32 channels. Since Cx40, Cx26, Cx50 and Cx37 gate at the positive side of V j, whereas Cx45 and Cx32 gate at negative V j, it is likely that V j behavior with respect to CO2-induced acidification varies depending on gating polarity, possibly involving the function of the postulated V j sensor (NH2-terminus).
The Journal of Membrane Biology – Springer Journals
Published: Jan 1, 2004
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