Voltage clamp analysis in isolated cardiac fibres as performed with two different perfusion chambres for double...

Voltage clamp experiments were performed on isolated frog atrial trabeculae disposed in 2 different perfusion chambres for double sucrose gap. In one of the perfusion chambres, a "liquid partition system" (L.P.S.) was used; in the other, a vaseline sealing (V.P.S.) method was used to separate the various fluid compartments. From the linear electrical properties, the elements of an apparent equivalent electrical circuit were calculated. The apparent nodal capacity was significantly larger in fibres disposed in the "liquid partition system" than those disposed in the "vaseline partition system". The apparent "error factor" resulting from the presence of the series resistance was larger in the L.P.S. than in the V.P.S. The apparent "error factor" becomes relatively large when the membrane conductance increases, such as during the flow of the inward current. A rapid desactivation of the peak inward current was found on bringing the command potential back to the resting potential in the V.P.S. This was not found in the L.P.S., indicating better voltage control with the V.P.S. than with the L.P.S. Transmembrane microelectrode recordings during voltage clamp experiment in the V.P.S. indicated satisfactory voltage control during the flow of the peak inward current. Adequate voltage control is lost when notches or irregularities appear on the current traces.