Differential suppression of delayed-rectifier and inwardly rectifier K+ currents by a group of ent-kaurane-type diterpenoids from Croton tonkinensis, in microglial cells

The Specific Effects of OD-1, a Peptide Activator, on Voltage-Gated Sodium Current and Seizure Susceptibility

OD-1, a scorpion toxin, has been previously recognized as an activator of voltage-gated Na⁺ currents. To what extent this agent can alter hippocampal neuronal Na⁺ currents and network excitability and how it can be applied to neuronal hyperexcitability research remains unclear. With the aid of patch-clamp technology, it was revealed that, in mHippoE-14 hippocampal neurons, OD-1 produced a concentration-, time-, and state-dependent rise in the peak amplitude of I_Na. It shifted the I_Na inactivation curve to a less negative potential and increased the frequency of spontaneous action currents. Further characterization of neuronal excitability revealed higher excitability in the hippocampal slices treated with OD-1 as compared with the control slices. A stereotaxic intrahippocampal injection of OD-1 generated a significantly higher frequency of spontaneous seizures and epileptiform discharges compared with intraperitoneal injection of lithium-pilocarpine- or kainic acid-induced epilepsy, with comparable pathological changes. Carbamazepine significantly attenuated OD-1 induced seizures and epileptiform discharges. The OD-1-mediated modifications of I_Na altered the electrical activity of neurons in vivo and OD-1 could potentially serve as a novel seizure and excitotoxicity model.

Characterization of Inhibitory Effectiveness in Hyperpolarization-Activated Cation Currents by a Group of ent-Kaurane-Type Diterpenoids from Croton tonkinensis

Croton is an extensive flowering plant genus in the spurge family, Euphorbiaceae. Three croton compounds with the common ent-kaurane skeleton have been purified from Croton tonkinensis. Methods: We examined any modifications of croton components (i.e., croton-01 [ent-18-acetoxy-7α-hydroxykaur-16-en-15-one], croton-02 [ent-7α,14β-dihydroxykaur-16-en-15-one] and croton-03 [ent-1β-acetoxy-7α,14β-dihydroxykaur-16-en-15-one] on either hyperpolarization-activated cation current (I_h) or erg-mediated K⁺ current identified in pituitary tumor (GH₃) cells and in rat insulin-secreting (INS-1) cells via patch-clamp methods. Results: Addition of croton-01, croton-02, or croton-03 effectively and differentially depressed I_h amplitude. Croton-03 (3 μM) shifted the activation curve of I_h to a more negative potential by approximately 11 mV. The voltage-dependent hysteresis of I_h was also diminished by croton-03 administration. Croton-03-induced depression of I_h could not be attenuated by SQ-22536 (10 μM), an inhibitor of adenylate cyclase, but indeed reversed by oxaliplatin (10 μM). The I_h in INS-1 cells was also depressed effectively by croton-03. Conclusion: Our study highlights the evidence that these ent-kaurane diterpenoids might conceivably perturb these ionic currents through which they have high influence on the functional activities of endocrine or neuroendocrine cells.