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 mu M) suppressed the amplitude of delayed rectifier K+ current (I-K(DR)) in a concentration-dependent manner with an IC50 value of 3.1 mu M. 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 mu M) or methyllyeaconitine (30 mu M) slightly suppressed I-K(DR) without modifying current decay. ACO (10 mu M) 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 mu M. 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. (C) 2008 Elsevier Ltd. All rights reserved.