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Am J Physiol Cell Physiol 273: C1721-C1731, 1997;
0363-6143/97 $5.00
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Vol. 273, Issue 5, C1721-C1731, November 1997

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

Raheela N. Khan1,2, Stephen K. Smith2, J. J. Morrison2, and Michael L. J. Ashford1

1 Department of Pharmacology, University of Cambridge, Cambridge CB2 1QJ; and 2 Department of Obstetrics and Gynaecology, University of Cambridge, The Rosie Maternity Hospital, Cambridge CB2 2SW, United Kingdom

Two populations, Ca2+-dependent (BKCa) and Ca2+-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 µM, respectively. Tetraethylammonium applied to outside-out patches decreased the unitary conductance of BKCa and BK channels, with dissociation constants of 423 and 395 µM, 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.

calcium-activated potassium channels; human myometrium; pregnancy; potassium channel blockers; tetraethylammonium; barium; ball peptide; charybdotoxin


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