Development of membrane conductance of chick skeletal muscle in culture. II. Effect of aminopyridines.

The effects of 4-aminopyridine and 3,4-diaminopyridine on membrane parameters during differentiation of embryonic chick skeletal muscle in culture have been studied. Both agents caused depolarization of fibres at all stages of development. In older cultures (day 6 onward), membrane conductance was suppressed by 0.1 mS cm-2. The addition of a maximal blocking concentration of tetraethylammonium to aminopyridine-treated fibres caused no further change in membrane conductance. In older cultures, it is concluded that the aminopyridines block resting potassium conductance. However in young fibres (day 3 to day 5), the aminopyridines caused an increase in membrane conductance. It is postulated that the aminopyridines increase membrane conductance to sodium or calcium or a combination of the two ions in immature muscle fibres.