CO2 sensitivity of voltage gating and gating polarity of gap junction channels - Connexin40 and its COOH-terminus-truneated mutant

摘要

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 Gj (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 CO, application. Similar results were obtained with Cx40-TR, Suggesting that CT does not play a role in this phenornenon. The sensitivity of Cx40 channels to 100% CO2 was also unaffected by CT truncation. There is evidence that CO, 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).