Effects of potassium channel openers on pentylenetetrazole-induced seizures in mice

The new anticonvulsant retigabine (D-23129) acts as an opener of K+ channels in neuronal cells

The patch-clamp technique was used to measure currents passing through K+ channels in neuronal cell preparations. Retigabine (D-23129, N-(2-amino-4-(4-fluorobenzylamino)-phenyl) carbamic acid ethyl ester) activated a K+ conductance in slightly depolarized NG108-15 neuronal cells in a dose-dependent manner (0.1-10 microM). At the K+ reversal potential, no current could be elicited and in hyperpolarized cells the current was reversed. A similar current was elicited in primary cultures of mouse cortical neurones and in differentiated hNT cells, a cell line derived from human neuronal cells. At higher concentrations, retigabine also partially blocked voltage activated K+ currents. None of the tested anticonvulsants, phenytoin, carbamazepine and valproate and none of the K+ channel openers cromakalim, diazoxide and pinacidil exerted a similar effect. The current was not affected by the K+ channel blocker glibenclamide (10 microM) but was fully blocked by application of Ba2+ (10.8 mM). Exchange of K+ with cesium in the intracellular space also fully abolished the current. It can be expected that the K+ channel opening effect contributes to the anticonvulsant activity of retigabine.

Potassium channel activation: a potential therapeutic approach?

The physiological role of K+ channel opening by endogenous substances (e.g., neurotransmitters and hormones) is a recognised inhibitory mechanism. Thus, the identification of novel synthetic molecules that 'directly' open K+ channels has led to a new direction in the pharmacology of ion channels. The existence of many different subtypes of K+ channels has been an impetus in the search for new molecules demonstrating channel and, thus, tissue selectivity. This review focuses on the different classes of openers of K+ channels, the intracellular mechanisms involved in the execution of their effects, and potential therapeutic targets.

Effect of four potassium channel agonists on bupivacaine-induced toxicity in mice

The influence of four potassium channel agonists i.e. diazoxide (D), levcromakalim (L), nicorandil (N) and pinacidil (P) on bupivacaine-induced acute toxicity was evaluated by measuring the convulsant activity, the time of latency to convulse and the mortality rate. Four different dosages (i.e. 0.1, 1, 10 and 100 mg/kg/i.p. for D, N and P and 0.01, 0.1, 1 and 5 mg/kg/i.p. for L) were injected to a total of 200 male NMRI adult mice: 16 groups of 10 mice each were previously treated by a single i.p. dose of each potassium channel agonist while controls (n = 40) received saline injection. Thus, 15 minutes later, all groups were injected with a 50 mg/kg/i.p. single dose of bupivacaine. The convulsant activity of bupivacaine was significantly modified by only high doses of L in a dose-dependent manner. Compared to the controls, the period of latency was significantly increased for most of the doses of P, N, D and L in a dose dependent manner for L and P. The anesthetic-induced mortality (47.5% for controls) was not significantly modified by D, but decreased by N and increased by high doses of L and P which is probably related to a delayed mortality.

ATP sensitive potassium channels: potential drug targets in neuropsychopharmacology

1. K channels are a diverse and ubiquitous class of proteins that regulate a number of biological functions. 2. Ligands for the study of a variety of K channels are available. These include "openers" and antagonists for the ATP sensitive K channel and peptide toxins such as apamin and charybdotoxin that block other subtypes. 3. Antagonists of the ATP sensitive K channel are useful in the treatment of type II diabetes while "openers" of this channel are being tested in asthma and cardiovascular disease. 4. Intracerebroventricular administration of K channel "openers" block experimentally induced seizures in rodents through a hyperpolarization of neurons. K channel openers may also be useful in the treatment of neurodegenerative diseases, pain and cerebral ischemia. 5. A key to the development of psychopharmacological agents to modify brain K channel function is CNS selectivity. The promise of the ATP sensitive K channel openers suggests a bright future for this mechanism.

BRL 38227--a potassium channel opener, antagonizes digoxin-induced convulsions

Experimental evidence suggests that potassium channel openers play an important role in convulsions. In this study, the anticonvulsant activity of BRL 38227, a new potassium channel opener against digoxin-induced convulsions, is reported. Intraventricular administration of digoxin (7.5 micrograms), included "popcorn-type" convulsions in rats. BRL 38227, injected centrally increased the onset time of convulsions and decreased the mortality rate in a dose-dependent manner. Pretreatment with 4-aminopyridine, a potassium channel blocker antagonized the protective effect of BRL 38227. These findings show the involvement of potassium channels in digoxin-induced convulsions. Further these results indicate that in the future potassium channels might be a target for new anticonvulsant drugs.