Characterization of aconitine-induced block of delayed rectifier K⁺ current in differentiated NG108-15 neuronal cells

The effects of aconitine (ACO), a highly toxic alkaloid, on ion currents in differentiated NG108-15 neuronal cells were investigated in this study. ACO (0.3-30 μM) suppressed the amplitude of delayed rectifier K⁺ current (I_K(DR)) in a concentration-dependent manner with an IC₅₀ value of 3.1 μM. The presence of ACO enhanced the rate and extent of I_K(DR) inactivation, although it had no effect on the initial activation phase of I_K(DR). It could shift the inactivation curve of I_K(DR) to a hyperpolarized potential with no change in the slope factor. Cumulative inactivation for I_K(DR) was also enhanced by ACO. Orphenadrine (30 μM) or methyllycaconitine (30 μM) slightly suppressed I_K(DR) without modifying current decay. ACO (10 μM) had an inhibitory effect on voltage-dependent Na⁺ current (I_Na). Under current-clamp recordings, ACO increased the firing and widening of action potentials in these cells. With the aid of the minimal binding scheme, the ACO actions on I_K(DR) was quantitatively provided with a dissociation constant of 0.6 μM. A modeled cell was designed to duplicate its inhibitory effect on spontaneous pacemaking. ACO also blocked I_K(DR) in neuroblastoma SH-SY5Y cells. Taken together, the experimental data and simulations show that ACO can block delayed rectifier K⁺ channels of neurons in a concentration- and state-dependent manner. Changes in action potentials induced by ACO in neurons in vivo can be explained mainly by its blocking actions on I_K(DR) and I_Na.