Effect of coriaria lactone on adenosine triphosphate-sensitive potassium channels in pyramidal neurons

Xiaoyi ZOU; Hua ZHOU; Shushun ZHOU

ABSTRACT

BACKGROUND:

Abnormal neuronal discharge arose from the activation of cell membrane ion channels and transmembrane ion transport. The electric activity of the cells is associated with cell metabolism fundamentally through adenosine triphosphate (ATP)-sensitive potassium(KATP) channels.Currently the involvement of KATP channels in the pathogenesis of epilepsy and the regulation of KATP channels by coriaria lacton (EL) remain unknown.OBJETCIVE To investigate the changes of cell membrane KATP channels in rat hippocampal neurons in response to CL as an epilepsy-inducing agent, and explore the role of KATP channels in the pathogenesis of epilepsy.

DESIGN:

Randomized controlled experiment.

SETTING:

Department of Neurology, West China Hospital Affiliated to Sichuan University, and Teaching and Research Section of Physiology,West China College of Preclinical Medicine and Forensic Medicine of Sichuan University.MATERIALS This experiment was carried out at Luzhou Medical College between May and December 2000. Hippocampus pyramidal neurons were obtained from neonatal Wistar rats and randomized into normal control group, tetraethylammonium chloride (TEA) group, DNP group, CL group, and electric conductance and dynamics group.

METHODS:

The hippocampus of newborn Wistar rats was separated under aseptic condition and cultured for 24 hours prior to treatment with 10 μmol/L cytarabine for selective cell culture for 7-10 days. The cells in good growth exhibiting typical morphology of pyramidal neurons were then selected for patch-clamp experiment. The cells in the normal control group were treated with normal saline, which was replaced by 5 mmol/L TEA in TEA group, by 30 μmol/L DNP then 0.5 mol/L ATP in DNP group, and by 1.0 mL/L CL then 1 μmol/L glibenclamide in CL group. In electric conductance and dynamics group, the clamp voltage was firstly adjusted to investigate the channel opening before CL was added to the cells.MAIN OUTCOME

MEASURES:

① Activity and curve of neuronal KATP channels; ② Effects of various clamp voltages on the channels activity and the effects of interventions with DNP, ATP and TEA; ③ Activation of neuronal membrane KATP channels induced by CL and the influence of glibenclamide.

RESULTS:

The reversal potential of the channels approximated 0 mV in homologous high-potassium solution. The opening of KATP channels increased along with the absolute value of the clamp voltage in a voltage-dependent manner, which was blocked by TEA. The electric current-voltage (Ⅰ-Ⅴ)curve could be fitted to a straight line with the electric conductance of (78.23±12.04) pS. Administration of 30 μmol/L DNP enhances the opening of the channels, which could be suppressed by 0.5 mol/L ATP.Addition of 1.0 mL/L CL to the cells caused obviously increased channel opening, which was suppressed by 1 μmol/L glibenclamide. The channel opening time was (1.754±0.060) ms for epileptic neuron τ01and (1.733±0.046) ms for normal neurons, showing no significant difference between them (n=25, t=0.147, P ＞ 0.05), but compared with the channel opening time of (2.441±0.265) ms for τ02 normal neurons, and duration was significantly prolonged in the epileptic neurons to reach (10.446±0.579)ms (n=25, t=0.000, P ＜ 0.01).

CONCLUSION:

The opening of KATP channels is responsible for reducing the action potential frequency for neuronal protection, which might be a negative feedback mechanism.