Selectivity and gating of the type L potassium channel in mouse lymphocytes.
Type l voltage-gated K+ channels in murine lymphocytes were studied under voltage clamp in cell-attached patches and in the whole-cell configuration. The kinetics of activation of whole-cell currents during depolarizing pulses could be fit by a single exponential after an initial delay. Deactivation upon repolarization of both macroscopic and microscopic currents was mono-exponential, except in Rb-Ringer or Cs-Ringer solution in which tail currents often displayed "hooks," wherein the current first increased or remained constant before decaying. In some cells type l currents were contaminated by a small component due to type n K+ channels, which deactivate approximately 10 times slower than type l channels. Both macroscopic and single channel currents could be dissected either kinetically or pharmacologically into these two K+ channel types. The ionic selectivity and conductance of type l channels were studied by varying the internal and external permeant ion. With 160 mM K+ in the cell, the relative permeability calculated from the reversal potential with the Goldman-Hodgkin-Katz equation was K+ (identical to 1.0) greater than Rb+ (0.76) greater than NH4+ = Cs+ (0.12) much greater than Na+ (less than 0.004). Measured 30 mV negative to the reversal potential, the relative conductance sequence was quite different: NH4+ (1.5) greater than K+ (identical to 1.0) greater than Rb+ (0.5) greater than Cs+ (0.06) much greater than Na+, Li+, TMA+ (unmeasurable). Single channel current rectification resembled that of the whole-cell instantaneous I-V relation. Anomalous mole-fraction dependence of the relative permeability PNH4/PK was observed in NH4(+)-K+ mixtures, indicating that the type l K+ channel is a multi-ion pore. Compared with other K+ channels, lymphocyte type l K+ channels are most similar to "g12" channels in myelinated nerve.
Shapiro
M S
MS
Department of Physiology, Rush Presbyterian St. Luke's Medical Center, Chicago, Illinois 60612.
DeCoursey
T E
TE
D000641:Ammonia / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D002469:Cell Separation; D002586:Cesium / Q000378:metabolism; D015640:Ion Channel Gating / Q000502:physiology*; D051379:Mice; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000502:physiology* / Q000648:ultrastructure; D012413:Rubidium / Q000378:metabolism; D013601:T-Lymphocytes / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure
D015221:Potassium Channels; D002586:Cesium; D000641:Ammonia; D012413:Rubidium; D011188:Potassium