The low conductance K(+) channel in human colonic crypt cells has a voltage-dependent permeability not affected by Mg(++).
The low conductance K(+) channel found in human colonocytes was investigated using the patch-clamp technique. The channel is Ca(++)-dependent and is blocked by Ba(++) (5 mM) with a decrease in open probability from 0.42 to 0.19. At -40 mV the slope conductance was 29 pS (using intracellular solution in the pipette). In inside-out patches, inward rectification was seen both with KCl (pipette)/NaCl (bath) solutions as well as KCl/KCl solutions. The rectification could not be affected by omitting Mg(++) from the pipette or the bath solution, neither by exposing the patches to the polyamine spermine (1 mM). Using the Goldman-Hodgkin-Katz equation we show that the permeability decreased in a linear fashion from approximately 5.2 x 10(-14) cm(3)/s to 1.8 x 10(-14) cm(3)/s (-100 to +100 mV), both with and without Mg(++) in the solutions. There was no significant difference in the nominal values of permeability. This property of the K(+) channel may facilitate the hyperpolarization needed to sustain a chloride secretion.
Sand
Peter
P
Department of Physiology and Pharmacology, Karolinska Institutet, 171 77 Stockholm, Sweden. peter.sand@fyfa.ki.se
Rydqvist
Bo
B
D001706:Biopsy; D002462:Cell Membrane / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D003106:Colon / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D003109:Colonic Diseases, Functional / Q000473:pathology; D004594:Electrophysiology; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D008274:Magnesium / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D051640:Small-Conductance Calcium-Activated Potassium Channels
D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D024661:Potassium Channels, Inwardly Rectifying; D051640:Small-Conductance Calcium-Activated Potassium Channels; D011189:Potassium Chloride; D008274:Magnesium