Single calcium-activated potassium channel in cultured mammary epithelial cells.
The properties of Ca2+-activated K+ channels in mouse mammary epithelial cells in primary culture were studied by the patch-clamp technique. In cell-attached patches, spontaneous channel openings were sometimes observed; the slope conductance of the currents was about 12 pS at negative membrane potentials with a physiological solution (152 mM Na+, 5.4 mM K+) in the pipette. External application of A23187, a calcium ionophore, activated this channel. In excised inside-out patches, the channel was activated by increasing the internal Ca2+ concentration (10(-7) to 10(-6) M). No voltage dependence of the channel was activated was observed. Internal Na+ blocked the outward K+ current in a voltage dependent manner and this block led to the non-linear I-V relationship at positive membrane potentials. The channel was blocked by internal Ba2+ (0.1 mM) and tetraethylammonium (TEA+, 20-50 mM). Ba2+ reduced the open probability but not the single channel conductance, whereas TEA+ reduced the single channel conductance. The single channel conductance of this channel, measured from the inward current with a high-K+ solution (150 mM K+) in the pipette, was large (about 40 pS), and showed inward rectification. These results suggest that this channel is different from the usual small conductance Ca2+-activated K+ channels observed in many other cells.
Furuya
K
K
National Institute for Physiological Sciences, Okazaki, Japan.
Enomoto
K
K
Furuya
S
S
Yamagishi
S
S
Edwards
C
C
Oka
T
T
D000818:Animals; D001464:Barium / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002412:Cations / Q000378:metabolism; D002478:Cells, Cultured; D004553:Electric Conductivity; D004594:Electrophysiology; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D007473:Ion Channels / Q000502:physiology; D008321:Mammary Glands, Animal / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D015221:Potassium Channels / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D002412:Cations; D007473:Ion Channels; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D001464:Barium; D000001:Calcimycin; D019789:Tetraethylammonium; D012964:Sodium; D002118:Calcium