Voltage-dependent potassium currents in developing neurones from quail mesencephalic neural crest.

Neurones in explants cultured from quail mesencephalic neural crest were studied at different stages of their development using the voltage-clamp technique. A voltage-dependent outward current activated by membrane depolarization was identified as a potassium current by the sensitivity of its reversal potential to extracellular potassium. The voltage-dependent potassium current is made up of two components which differ in their sensitivity to 4-aminopyridine (4-AP) and tetraethylammonium (TEA). The component most sensitive to 4-AP has fast activation kinetics and inactivates quickly at sustained depolarized voltages. By analogy with a current described in other preparations, this current was called IA. The component most sensitive to TEA has slower activation kinetics and inactivates more slowly at sustained depolarized voltages. This current was called IK. IA and IK were already present in neurones cultured for 24 h. The ratio between the peak of IK and that of IA increased significantly between 24 h and 4 days in culture. This means that the two components of the voltage-dependent potassium current follow a different time course during development.