Inhibition of sodium current by carbamazepine in dorsal root ganglion neurons in vitro.

Carbamazepine (CBZ), one of the most commonly prescribed antiepileptic drug, is proposed to inhibit Na+ channel. In this study, we have investigated the effects of CBZ on Na+ current, evoked in cultured dorsal root ganglion (DRG) neurons from neonatal rats using whole cell patch clamp technique. In small DRG neurons (20–25 μm), Na+ current was obtained by blocking K+ and Ca2+ currents with appropriate ion replacement and channel blockers. Separation of the Na+ current components was achieved on the basis of response to the conditioning voltage. The CBZ depressed Na+ current in a dose-dependent manner. The maximal Na+ current was depressed at 300 μM of CBZ, where 94±5.1% of depression was observed. The depression of normalized current amplitude was found to be 72±13.2%, 84±10%, 85±7.1% and 95±5.2% at 10, 30, 100 and 300 μM of CBZ concentrations, respectively, at –20 mV test pulse, when compared with control. The depression of current amplitude was observed as 48±12.3%, 42±15.2%, 71±17.7% and 90±5.8% at 10, 30, 100 and 300 μM of CBZ concentration, respectively, at 0 mV voltage pulse. The depression of Na+ currents was found to be dose-dependant at –20 and –10 mV but not at 0 mV. It is concluded that the depression of Na+ currents by CBZ may be responsible for inhibiting the neurotransmitter release.

Protective effect of adenosine in diabetic neuropathic pain is mediated through adenosine A1-receptors.

Diabetic neuropathic pain is generally considered to be one of the most troublesome complications affecting diabetic patients and current therapy provides inadequate pain relief. In the present study, the effect of adenosine was investigated in a model of diabetic neuropathic pain. Diabetes was induced by streptozotocin (65 mg/kg, ip) in male Sprague Dawley rats and subjected to thermal (cold and hot) and chemical (formalin) stimuli. Diabetic rats developed hyperalgesia by the end of six weeks in thermal and chemical stimuli test. Adenosine (100, 200 and 500 mg/kg, ip) produced significant reversal of responses to thermal and chemical stimuli in diabetic rats. 8-Cyclopentyl-1, 3-dipropylxanthine (DPCPX 1 mg/kg, ip), an adenosine A1-receptor antagonist, but not 3,7-dimethyl-l-propargylxanthine (DMPX 1 mg/kg, ip), an adenosine A2A-receptor antagonist, reversed the protective effect of adenosine. These results indicate that adenosine is an effective analgesics in a model of diabetic neuropathy, and the protection produced by adenosine is via stimulation of adenosine A1-receptors.