PH SENSITIVITY OF THE CARDIAC GAP JUNCTION PROTEINS, CONNEXIN45 AND CONNEXIN43

Intercellular communication through gap junction channels can be regulated by changes in intracellular pH (pH(i)). This regulation may play an important role in ischemic heart tissue. Using the dual voltage-clamp technique, we compared the pH(i) sensitivity of gap junction channels composed of connexin 43 (Cx43) and Cx45, two of the gap junction proteins that are expressed in heart. We made use of SKHep1 cells, endogenously expressing low levels of Cx45 and SKHep1 cells stably transfected with rat Cx43. To manipulate the pH(i) we applied the NH3/NH4+ pH-clamp method. At pH(i) 6.7 the g(j) of Cx45 channels was reduced to similar to 20% of control values (pH(i) 7.0) and at pH(i) 6.3 all channels closed. The g(j) of Cx43 channels was similar to 70% of control values at pH(i) 6.7 and similar to 40% at pH(i) 6.3. Cx43 channels closed at pH(i) 5.8. Single channel conductances were 17.8 pS for Cx45 and 40.8 pS for Cx43 at pH(i) 7.0 and did not change significantly at lower pH(i). This suggests that the decrease in macroscopic conductance observed at low pH, results from the decrease in open probability of gap junctional channels rather than from a decrease in single channel conductance. Our results demonstrate that gap junction channels built of Cx45 are far more pH sensitive than channels built of Cx43.