Abstract
Blockade of voltage-gated sodium (Na+) channels by local anesthetics represents the main mechanism for inhibition of impulse propagation. Local anesthetic-induced potassium (K+) channel inhibition is also known to influence transmission of sensory impulses and to potentiate inhibition. K+ channels involved in this mechanism may belong to the emerging family of background tandem pore domain K+ channels (2P K+ channels). To determine more precisely the effects of local anesthetics on members of this ion channel family, we heterologously expressed the 2P K+ channels TASK-2 (KCNK5), TASK-1 (KCNK3), and chimeric TASK-1/TASK-2 channels in oocytes of Xenopus laevis. TASK-2 cDNA-transfected HEK 293 cells were used for single-channel recordings. Local anesthetic inhibition of TASK-2 was dose-dependent, agent-specific, and stereoselective. The IC50 values for R-(+)-bupivacaine and S-(–)-bupivacaine were 17 and 43 μM and for R-(+)-ropivacaine and S-(–)-ropivacaine, 85 and 236 μM. Lidocaine (1 mM) inhibited TASK-2 currents by 55 ± 4%, whereas its quaternary positively charged analog N-ethyl lidocaine (QX314) had no effect. Bupivacaine (100 μM) decreased channel open probability from 20.8 ± 1.6% to 5.6 ± 2.2%. Local anesthetics [300 μM R-(+)-bupivacaine] caused significantly greater depolarization of the resting membrane potential of TASK-2-expressing oocytes compared with water-injected control oocytes (15.8 ± 2.5 mV versus 0.1 ± 0.05 mV; p < 0.001). Chimeric TASK-1/TASK-2 2P K+ channel subunits that retained pH sensitivity demonstrated that the carboxy domain of TASK-2 mediates the greater local anesthetic sensitivity of TASK-2. These results show that clinically achievable concentrations of local anesthetics inhibit background K+ channel function and may thereby enhance conduction blockade.
Footnotes
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This research was supported by National Institutes of Health Grant GMS-51372 (C.S.Y.) and financial institutional resources from the Anesthesia Department, Kantonsspital, University Clinics, Basel (C.H.K.).
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DOI: 10.1124/jpet.103.049809.
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ABBREVIATIONS: 2P, tandem pore domain; CNS, central nervous system; TASK, TWIK (tandem pore weak inward rectifying K channel)-related acid-sensitive K+ channel; TOK, two pore domains outward-rectifying K+ channel; TREK, TWIK-related K+ channel; δ, fractional electrical distance; QX314, N-ethyl lidocaine; FR, frog Ringer's solution; nH, Hill coefficient; PCR, polymerase chain reaction; pHm, pH value for 50% of inhibition; Po, open probability; τ, time constant of activation; IQB-9302, ciprocaine.
- Received January 30, 2003.
- Accepted March 17, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
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