Effects of 4-aminopyridine on calcium action potentials and calcium current under voltage clamp in spinal neurons.

We examined the effects of 4-aminopyridine (4-AP) on calcium conductance mechanisms in cultured mouse spinal cord neurons. At low concentrations (less than or equal to 1 mM), 4-AP enhanced Ca2+-dependent transmitter release and prolonged the duration of Ca2+-dependent action potentials. Voltage clamp studies indicated that 4-AP directly facilitates Ca2+ entry through voltage sensitive channels apart from an effect on K+ currents. These results may help to explain why the drug promotes Ca2+-dependent transmitter release at peripheral and central synapses.