Evidence for Inhibitory Perturbations on the Amplitude, Gating, and Hysteresis of A-Type Potassium Current, Produced by Lacosamide, a Functionalized Amino Acid with Anticonvulsant Properties

Lacosamide (Vimpat(®), LCS) is widely known as a functionalized amino acid with promising anti-convulsant properties; however, adverse events during its use have gradually appeared. Despite its inhibitory effect on voltage-gated Na(+) current (I(Na)), the modifications on varying types of ionic currents caused by this drug remain largely unexplored. In pituitary tumor (GH(3)) cells, we found that the presence of LCS concentration-dependently decreased the amplitude of A-type K(+) current (I(K(A))) elicited in response to membrane depolarization. The I(K(A)) amplitude in these cells was sensitive to attenuation by the application of 4-aminopyridine, 4-aminopyridine-3-methanol, or capsaicin but not by that of tetraethylammonium chloride. The effective IC(50) value required for its reduction in peak or sustained I(K(A)) was calculated to be 102 or 42 µM, respectively, while the value of the dissociation constant (K(D)) estimated from the slow component in I(K(A)) inactivation at varying LCS concentrations was 52 µM. By use of two-step voltage protocol, the presence of this drug resulted in a rightward shift in the steady-state inactivation curve of I(K(A)) as well as in a slowing in the recovery time course of the current block; however, no change in the gating charge of the inactivation curve was detected in its presence. Moreover, the LCS addition led to an attenuation in the degree of voltage-dependent hysteresis for I(K(A)) elicitation by long-duration triangular ramp voltage commands. Likewise, the I(K(A)) identified in mouse mHippoE-14 neurons was also sensitive to block by LCS, coincident with an elevation in the current inactivation rate. Collectively, apart from its canonical action on I(Na) inhibition, LCS was effective at altering the amplitude, gating, and hysteresis of I(K(A)) in excitable cells. The modulatory actions on I(K(A)), caused by LCS, could interfere with the functional activities of electrically excitable cells (e.g., pituitary tumor cells or hippocampal neurons).