Properties of single gap junctional channels between isolated neonatal rat heart cells

The electrophysiological properties of single cardiac gap junctional channels that evolve one after another during the process of coupling between pairs of isolated neonatal rat heart myocytes obtained by enzymatic dispersion were investigated. Adjacent cells were brought in contact with each other by pushing them together by means of suction microelectrodes, which allow simultaneous voltage- or current-clamp recordings from each cell. Under these circumstances, the junctional channels had quite different properties from those reported in the literature. As long as only a few channels were present, they exhibited marked voltage-dependent gating as measured under voltage-clamp conditions and tended to close when transjunctional voltages greater than 50 mV were applied. Their single-channel conductance, depending on the composition of the solution in the recording pipettes, was approximately 45 or 60 pS, but also a lower conductance of 20 or 30 pS was encountered. As the junctional conductance increased concomitantly with an increase in the number of channels, this voltage dependence gradually diminished and eventually seemed to have disappeared completely. At that stage, the electrical properties of these newly formed junctions were identical with those of gap junctions between well-coupled cell pairs isolated as such.