CHARACTERIZATION OF LARGE-CONDUCTANCE, CALCIUM-ACTIVATED POTASSIUM CHANNELS FROM HUMAN MYOMETRIUM

OBJECTIVES: The purpose of our study was to detect and characterize potassium channels in the plasma membrane of smooth muscle cells from human myometrium. STUDY DESIGN: 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 almost-equal-to 220 mumol/L) and charybdotoxin (dissociation constant almost-equal-to 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). CONCLUSION: 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.