Abstract Myocytes from neonatal rat hearts were used to assess the conductive properties of gap junction channels by means of the dual voltage-clamp method. The experiments were carried out on three types (groups) of preparations: (1) induced cell pairs, (2) preformed cell pairs with few gap junction channels (1 to 3 channels), and (3) preformed cell pairs with many channels (100 to 200 channels) after treatment with uncoupling agents such as SKF-525A (75 μmol/L), heptanol (3 mmol/L), and arachidonic acid (100 μmol/L). In group 1, the first opening of a newly formed channel was slow (20 to 65 ms) and occurred 7 to 25 minutes after physical cell contact. The rate of channel insertion was 1.3 channels/min. Associated with a junctional voltage gradient (V j ), the channels revealed multiple conductances, a main open state [γ j (main state)], several substates [γ j (substates)], and a residual state [γ j (residual state)]. On rare occasions, the channels closed completely. The same phenomena were observed in groups 2 and 3. The existence of γ j (residual state) provides an explanation for the incomplete inactivation of the junctional current (I j ) at large values of V j in cell pairs with many gap junction channels. The values of γ j (main state) and γ j (residual state) gained from groups 1, 2, and 3 turned out to be comparable and hence were pooled. The fit of the data to a Gaussian distribution revealed a narrow single peak for both conductances. The values of γ j were dependent on the composition of the pipette solution. Solutions were as follows: (1) KCl solution, γ j (main state)=96 pS and γ j (residual state)=23 pS; (2) Cs + aspartate − solution, γ j (main state)=61 pS and γ j (residual state)=12 pS; and (3) tetraethylammonium + aspartate − solution, γ j (main state)=19 pS and γ j (residual state)=3 pS. The respective γ j (main state)-to-γ j (residual state) ratios were 4.2, 5.1, and 6.3. This indicates that the residual state restricts ion permeation more efficiently than does the main state. Transitions of I j between open states (main open state, substates, and residual state) were fast (<2 ms), and transitions involving the closed state and an open state were slow (15 to 65 ms). This implies the existence of two gating mechanisms. The residual state may be regarded as the ground state of electrical gating controlled by V j ; the closed state, as the ground state of chemical gating.

Valiunas, V., Bukauskas, F. F., & Weingart, R. (1997). Conductances and Selective Permeability of Connexin43 Gap Junction Channels Examined in Neonatal Rat Heart Cells. Circulation Research, 80(5), 708–719.