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 microM) suppressed the amplitude of delayed rectifier K+ current (I K(DR)) in a concentration-dependent manner with an IC50 value of 3.1 microM. 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 microM) or methyllycaconitine (30 microM) slightly suppressed I K(DR) without modifying current decay. ACO (10 microM) 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 microM. 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.
Lin
Ming-Wei
MW
Institute of Basic Medical Sciences, National Cheng Kung University Medical College, Tainan, Taiwan.
Wang
Ya-Jean
YJ
Liu
Shiuh-Inn
SI
Lin
An-An
AA
Lo
Yi-Ching
YC
Wu
Sheng-Nan
SN
D000157:Aconitine / Q000494:pharmacology*; D000200:Action Potentials / Q000187:drug effects; D000465:Algorithms; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D051668:Delayed Rectifier Potassium Channels / Q000187:drug effects*; D004594:Electrophysiology; D006801:Humans; D007700:Kinetics; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers
D051668:Delayed Rectifier Potassium Channels; D026902:Potassium Channel Blockers; D000157:Aconitine