Conduction properties of the M-channel in rat sympathetic neurons.
We have investigated the conduction properties of the M-channel in rat superior cervical ganglion neurons. Reversal potentials measured under bi-ionic conditions yielded a permeation sequence of Tl > K > Rb > Cs > NH4 > Na. Slope conductances gave a conductance sequence of K > Tl > NH4 > Rb > Cs. M-current was shown to exhibit a number of features atypical of potassium channels. First, the conduction of monovalent cations relative to K was very low. Second, the nature of the permeant ion did not affect the deactivation kinetics. Third, M-current did not exhibit anomalous mole-fraction behavior, a property suggestive of a multi-ion pore. Finally, external Ba, which is a blocker of M-current, showed a preferential block of outward current and had much less effect on inward current. The permeability sequence of the M-channel is very similar to other K-selective channels, implying a high degree of conservation in the selectivity filter. However, other conduction properties suggest that the pore structure outside of the selectivity filter is very different from previously cloned potassium channels.
Cloues
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Vollum Institute, Oregon Health Sciences University, Portland 97201, USA. clouesr@ohsu.edu
Marrion
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D000818:Animals; D001464:Barium / Q000494:pharmacology; D055592:Biophysical Phenomena; D001703:Biophysics; D002414:Cations, Monovalent / Q000378:metabolism; D002478:Cells, Cultured; D004553:Electric Conductivity; D007700:Kinetics; D009474:Neurons / Q000378:metabolism*; D010539:Permeability; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D017783:Superior Cervical Ganglion / Q000378:metabolism*
D002414:Cations, Monovalent; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D001464:Barium