Junctional communication between isolated pairs of canine atrial cells is mediated by homogeneous and heterogeneous gap junction channels

Introduction: The expression of multiple connexins (Cxs) in the canine righ t atria raises the possibility that heterogeneous gap junction channels mig ht be formed. Methods and Results: We compared the unitary conductance (gamma(j)) of gap junction channels between isolated canine atrial cell pairs with those of h omogeneous cardiac gap junction channels expressed in other systems. After partial uncoupling with halothane (2 mmol/L), the gamma(j) calculations for atrial isolated cardiocytes ranged from 30 to 220 pS and their distributio n in event histograms was spread over the entire range, with a small peak a t similar to 100 pS. This distribution deviates from the discrete peaks cal culated from gamma(j) of homogeneous channels. All-points histograms of jun ctional current traces revealed distinct open-state levels. Some of these a re related to the main open state of connexin43 (Cx43) (similar to 100 pS), observed between canine ventricular cells, or connexin40 (Cx40) (similar t o 215 pS) observed between transfected N2A cells under similar recording co nditions. Intermediate values for gamma(j) were not observed in recordings from ventricular cells, which express mostly Cx43, nor in those from N2A ce lls expressing Cx40, but were observed consistently between atrial cells. B ecause they were measured as first openings from the nonconductance state, these intermediate values most likely represent main conductance states of heterogeneous channels rather than subconductance states of homogeneous cha nnels. Conclusion: This suggests that regulation of cell-to-cell coupling in the h eart depends not only on posttranslational modulation of preexisting Cxs, b ut also on the intracellular assembly mechanisms, and the way individual Cx s interact with others within a connexon and/or with other connexons from a djacent cells.