Ca²⁺ dependence and pharmacology of large-conductance K⁺ channels in nonlabor and labor human uterine myocytes

Dec 31, 1997The American journal of physiology

Calcium Dependence and Drug Response of Large Potassium Channels in Human Uterine Muscle Cells Before and During Labor

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Abstract

Two populations of large conductance K+ channels were identified in human pregnant myometrial cells, with significantly different properties between laboring and nonlaboring patients.

BKCa channels in nonlabor myometrial cells showed a low open-state probability, while labor myometrial cells exhibited either no openings or high, oscillatory activity.
Ba2+, 4-aminopyridine, and a specific peptide blocked BKCa channels more effectively than BK channels.
Tetraethylammonium reduced the unitary current amplitude of both BKCa and BK channels, with different dissociation constants (46 mM for BKCa and 53 µM for BK).
Outside-out patches showed tetraethylammonium decreased unitary conductance for BKCa and BK channels, with dissociation constants of 423 µM and 395 µM, respectively.
The findings indicate that myometrial K+ channel properties differ significantly between laboring and nonlaboring patients.

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Two populations, Ca(2+)-dependent (BKCa) and Ca(2+)-independent K+ (BK) channels of large conductance were identified in inside-out patches of nonlabor and labor freshly dispersed human pregnant myometrial cells, respectively. Cell-attached recordings from nonlabor myometrial cells frequently displayed BKCa channel openings characterized by a relatively low open-state probability, whereas similar recordings from labor tissue displayed either no channel openings or consistently high levels of channel activity that often exhibited clear, oscillatory activity. In inside-out patch recordings, Ba2+ (2-10 mM), 4-aminopyridine (0.1-1 mM), and Shaker B inactivating peptide ("ball peptide") blocked the BKCa channel but were much less effective on BK channels. Application of tetraethylammonium to inside-out membrane patches reduced unitary current amplitude of BKCa and BK channels, with dissociation constants of 46 mM and 53 microM, respectively. Tetraethylammonium applied to outside-out patches decreased the unitary conductance of BKCa and BK channels, with dissociation constants of 423 and 395 microM, respectively. These results demonstrate that the properties of human myometrial large-conductance K+ channels in myocytes isolated from laboring patients are significantly different from those isolated from nonlaboring patients.

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Ca²⁺ dependence and pharmacology of large-conductance K⁺ channels in nonlabor and labor human uterine myocytes

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