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Abstract: Mutations of Cx40 (GJA5) have been identified in people with lone chronic atrial fibrillation including G38D and M163V which were found in the same patient. We used dual whole cell patch clamp procedures to examine the transjunctional voltage (V j) gating and channel conductance properties of these two rare mutants. Each mutant exhibited slight alterations of V j gating properties and increased the gap junction channel conductance (γ j) by 20–30pS. While co-expression of the two mutations had similar effects on V j gating, it synergistically increased γ j by 50%. Unlike WTCx40 or M163V, G38D induced activity of a dominant 271pS hemichannel. [Copyright &y& Elsevier]

With two independent patch electrodes sealed to small clusters of electrically coupled chick embryo cardiac cells, we have measured four parameters: true seal and patch resistance, channel conductance, and membrane potential. One electrode was in the cell-attached mode, and recorded current flowing in parallel through the membrane patch and seal. The second electrode, sealed on a different cell in the cluster, was in the whole cell recording configuration, and served to record or control the membrane potential of the cluster. We fit the four measured parameters to a simple electrical model to reveal errors not usually recognized in the patch-clamp technique. Among these are the following: (1) The apparent seal resistance, determined by changing the potential in a patch electrode, may be a poor estimate of true seal resistance, since it includes the parallel combination of seal- and patch-resistance. (2) Patch resistance may be influenced by the electrode filling solution, and is often much lower than is usually assumed. (3) With a small cell preparation that has an input resistance in the gigaohm range, measurements of single-channel conductance using a cell-attached patch electrode may be inaccurate because cell membrane potential does not remain constant as electrode potential is varied. [ABSTRACT FROM AUTHOR]