Pharmacological Modulation Of Recombinant Human Two-Pore Domain K+ Channels : Whole-Cell patch-Clamp Analysis
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Background potassium currents play an important role in the regulation of the resting membrane potential and excitability of mammalian neurons. Recently cloned two- pore domain potassium channels (K2p) are believed to underlie these currents. The roles of K2P channels in general anesthesia and neuroprotection have been proposed recently. In view of this, we investigated the ability of trichloroethanol (an active metabolite of the non-volatile general anesthetic cldoral hydrate, widely used as a pediatric sedative) to modulate the activity of human TREK-1 and TRAAK channels. We found that trichloroethanol potently activates both hTREK-1 and hTRAAK channels at pharmacologically relevant concentrations. The parent compound chloral hydrate was also found to augtnent the activity of both the channels reversibly. Studies with carboxy- terminal deletion mutants (hTREK-1A89, hTREK-1 A100 and hTREK-1 A1 19), suggested that C-terminal tail is not essential for the activation of TREK-1 by trichloroethanol. Our findings identify TREK-1 and TRCL4K channels as molecular targets for trichloroethanol and we propose that activation of both these channels might contribute to the CNS depressant effects of chloral hydrate. Another channel TASK-2, which is essentially absent in the human brain was also found to be potently activated by both trichloroethanol and chloral hydrate. In another series of experiments, we studied the effects of methyl xanthines caffeine and theophylline on hTREK-1 channels. Caffeine and theophylline are used for therapeutic purposes and frequently cause life-threatening convulsive seizures due to systemic toxicity. The mechanisms for the epileptogenicity of caffeine and theophylline are not clear. Recent experiments using knockout mice provided direct evidence for a role for TREK-1 in the control of epileptogenesis. We hypothesized that the epileptogenicity of caffeine and theophylline may be related to the inhibition of TREK-1 channels. We investigated this possibility and observed massive inhibition of TREK-1 channels at toxicologically relevant concentrations. Experiments with the mutant TREK-1 channel (S348A mutant) suggested the involvement of cANP/PKA pathway in the inhibition of TREK-1 channels by caffeine and theophylline. We suggest that inhibition of TREK-1 channels may contribute to the convulsive seizures induced by toxic levels of caffeine and theophylline. Local anesthetics exhibit their clinical effects not only by binding to voltage-gated sodium channels, but also by interacting with other ion channels such as potassium channels. Because of the physiological significance of TREK-1 channels and their abundant expression in peripheral sensory neurons, we investigated the effects of lidocaine to see whether its interaction with 'REK-1 channels contribute to the conduction blockade. Lidocaine caused dose-dependent inhibition of TREK-1channels and the inhibition was voltage-independent. Cytoplasmic C-terminal tail is critically required for lidocaine action. Inhibition of TREK-1 channels is achieved at concentrations for iiz vivo action and this effect may have implications for the clinically observed drug action of lidocaine.
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