Intracellular Ca2+-ions inactivate K+-current in bullfrog sympathetic neurons.

Neurons from bullfrog sympathetic ganglia were voltage clamped using a single microelectrode, in a sodium-free, calcium-rich solution containing tetraethylammonium. A brief inward calcium current was followed by a long-lasting inward current. The long-lasting inward current corresponded to a depolarizing afterpotential which followed a calcium spike under the current clamp. It was largely due to the M-channel closure. The present study indicates that massive calcium entry can cause inactivation of potassium conductance in vertebrate neurons.