Asymmetry of Rb+ conduction emerged under bi-ionic conditions in epithelial maxi-K+ channels.
K(+) channels permit more than one ion within their conducting pathway at any given moment and show a saturating single-file behavior. The conduction of Rb(+) shows an unusual behavior, a so-called "Rb(+) anomaly," and it has been used to probe the mechanism of the ion conduction through K(+)-selective channels. Under the bi-ionic condition of K(+) and Rb(+), we carried out patch-clamp single-channel current measurements in MaxiK(+) channels from mouse submandibular acinar cells. Keeping only K(+) on one side of the membrane while varying fractional Rb(+) concentration on the opposite, we had a series of current-voltage relationships. It showed a characteristic inflection at which the ion conductance was divided into two components, one ascribed to pure K(+) conduction and the other to K(+) and Rb(+) bi-ionic conduction. By analyzing the latter, we depicted that (1) the bi-ionic conductance showed a characteristic reduction curve as the Rb(+) fractional concentration increased; (2) Rb(+) can bind the channel more tightly when it accesses from the outside than from the inside. Thus we conclude that such asymmetry of the Rb(+) binding determines the pattern of bi-ionic conductance reduction in K-selective channels.
Department of Physiology, Tohoku University Graduate School of Medicine, Seiryo-cho 2-1, Aoba-ku, Sendai, 980-8575 Japan.
Atsushi
A
Ohsaga
Yoshimichi
Y
Murata
Yoshiaki
Y
Kondo
Riichiro
R
Hira
Yoshio
Y
Maruyama
D000818:Animals; D004847:Epithelial Cells / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials; D051379:Mice; D008954:Models, Biological; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism*; D013363:Submandibular Gland / Q000166:cytology / Q000378:metabolism*
D051036:Large-Conductance Calcium-Activated Potassium Channels; D012413:Rubidium; D011188:Potassium