Determinants of the anesthetic sensitivity of two-pore domain acid-sensitive potassium channels - Molecular cloning of an anesthetic-activated potassium channel from Lymnaea stagnalis

Certain two-pore domain K+ channels are plausible targets for volatile general anesthetics, yet little is known at the molecular level about how these simple agents cause channel activation. The first anesthetic-activated K+ current I-K(An) that was characterized was discovered in the mollusk Lymnaea stagnalis and is remarkable for both its sensitivity to general anesthetics and its stereo-selective responses to anesthetic enantiomers (Franks, N. P., and Lieb, W. R. (1988) Nature 333, 662-664 and Franks, N. P., and Lieb, W. R. (1991) Science 254, 427-430). Here we report the molecular cloning of a two-pore domain K+ channel LyTASK from L. stagnalis and show that, when expressed in HEK-293 cells, it displays the same biophysical characteristics as the anesthetic-activated K+ current I-K(An). Sequence analysis and functional properties show it to be a member of the TASK family of channels with similar to 47% identity at the amino acid level when compared with human TASK-1 and TASK-3. By using chimeric channel constructs and site-directed mutagenesis we have identified the specific amino acid 159 to be a critical determinant of anesthetic sensitivity, which, when mutated to alanine, essentially eliminates anesthetic activation in the human channels and greatly reduces activation in LyTASK. The L159A mutation in LyTASK disrupts the stereo-selective response to isoflurane while having no effect on the pH sensitivity of the channel, suggesting this critical amino acid may form part of an anesthetic binding site.