Characterization of large-conductance, calcium-activated potassium channels from human myometrium.
OBJECTIVE
The purpose of our study was to detect and characterize potassium channels in the plasma membrane of smooth muscle cells from human myometrium.


METHODS
Plasma membrane vesicles were incorporated into lipid bilayers to record single potassium channel activity.


RESULTS
We predominantly found a "maxi" calcium-activated potassium channel (261 picosiemens). This channel was calcium (micromoles per liter range) and voltage sensitive, highly selective for K+ over Na+ and Cs+, and was sensitive to external tetraethylammonium (dissociation constant approximately 220 mumol/L) and charybdotoxin (dissociation constant approximately 23 nmol/L). External apamin and 4-aminopyridine had no effect on this channel. Another type of potassium channel that was less frequently observed was also identified. It had a smaller conductance (142 picosiemens) and it seemed to be calcium independent (up to 50 nmol/L).


CONCLUSIONS
Human myometrium possesses abundant "maxi" calcium-activated potassium channels. This channel shares common characteristics with other "maxi" calcium-activated potassium channels, including calcium and voltage gating, high conductance and selectivity, and channel pharmacologic profile.
Pérez
G J
GJ
Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX 77030.
Toro
L
L
Erulkar
S D
SD
Stefani
E
E
D002118:Calcium / Q000494:pharmacology*; D018999:Charybdotoxin; D004553:Electric Conductivity; D005260:Female; D006801:Humans; D007477:Ions; D009215:Myometrium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D012604:Scorpion Venoms / Q000494:pharmacology; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D007477:Ions; D015221:Potassium Channels; D012604:Scorpion Venoms; D013757:Tetraethylammonium Compounds; D018999:Charybdotoxin; D019789:Tetraethylammonium; D002118:Calcium