Development of membrane conductance of chick skeletal muscle in culture

Resting membrane potentials and membrane conductances of chick skeletal muscle in culture were determined from the 3rd to the 10th day after plating. The effect of tetraethylammonium (TEA) and of replacement of potassium with caesium on these parameters was investigated. Resting membrane potential (Em) rises during myogenesis in vitro and resting membrane conductance (Gm) falls. The initial level of Gm was relatively high (1.2 mS cm-2) but this fell to a final level around 0.2 mS cm-2. The most rapid changes in both parameters occurred between days 3 and 5 of culture. Both TEA and caesium depressed Em and Gm at all stages of development. On the 3rd day of culture Gm was reduced by 0.2 mS cm-2 by both agents. Thereafter, Gm was depressed by about 0.1 mS cm2. Caesium does not penetrate potassium channels and the reduction in Gm is attributed to block of these channels. This indicates that resting potassium conductance is relatively constant at 0.1 mS cm-2 throughout muscle fibre development. Because TEA produces changes in Gm similar to those produced by caesium, TEA is concluded to be acting at the potassium channel in a manner similar to caseium.