Nootropic agent vinpocetine blocks delayed rectified potassium currents more strongly than high-threshold calcium currents.

A two-microelectrode potential clamping method was used on isolated common snail neurons to measure high-threshold Ca2+ and delayed rectified K+ currents. Addition of the nootropic agent vinpocetine (VPC) to the bathing solution rapidly and reversibly inhibited both types of current. The effects of VPC were dose-dependent and were independent of the test stimulus voltage. Maximum blockade of the Ca2+ current averaged 27% at a VPC concentration of 600 microM. Maximum blockade of the K+ current averaged 76% at a VPC concentration of 30 microM. It is concluded that K+ channels are more likely targets of VPC than Ca2+ channels.