Functional coupling of beta3-adrenoceptors and large conductance calcium-activated potassium channels in human uterine myocytes.
BACKGROUND
Beta3-adrenoreceptor modulation in human myometrium during pregnancy is linked functionally to myometrial inhibition. Maxi-K+ channels (BK(Ca)) play a significant role in modulating cell membrane potential and excitability.


OBJECTIVE
This study was designed to investigate the potential involvement of BK(Ca) channel function in the response of human myometrium to beta3-adrenoceptor activation.


METHODS
Single and whole-cell electrophysiological BK(Ca) channel recordings from freshly dispersed myocytes were obtained in the presence and absence of BRL37344, a specific beta3-adrenoreceptor agonist. The in vitro effects of BRL37344 on isolated myometrial contractions, in the presence and absence of the specific BK(Ca) channel blocker, iberiotoxin (IbTX), were investigated.


METHODS
The study was carried out at the Clinical Science Institute.


METHODS
Myometrial biopsies were obtained at elective cesarean delivery.


METHODS
No intervention was applied.


METHODS
Open state probability of single channel recordings, whole cell currents, and myometrial contractile activity were measured.


RESULTS
Single-channel recordings identified the BK(Ca) channel as a target of BRL37344. BRL37344 significantly increased the open state probability of this channel in a concentration-dependent manner (control 0.031 +/- 0.004; 50 microM BRL37344 0.073 +/- 0.005 (P < 0.001); and 100 microM BRL37344 0.101 +/- 0.005 (P < 0.001). This effect was completely blocked after preincubation of the cells with 1 microM bupranolol, a nonspecific beta-adrenoreceptor blocker, or 100 nM SR59230a, a specific beta3-adrenoreceptor antagonist. In addition, BRL37344 increased whole-cell currents over a range of membrane potentials, and this effect was reversed by 100 nM IbTX. In vitro isometric tension studies demonstrated that BRL37344 exerted a significant concentration-dependent relaxant effect on human myometrial tissue (P < 0.05), and preincubation of these strips with IbTX attenuated this effect on both spontaneous and oxytocin-induced contractions (44.44 and 57.84% at 10(-5) M, respectively).


CONCLUSIONS
These findings outline that activation of the BK(Ca) channel may explain the potent uterorelaxant effect of beta3-adrenoreceptor agonists.
Doheny
Helen C
HC
Department of Obstetrics and Gynecology, National University of Ireland Galway, Clinical Science Institute, University College Hospital Galway, Galway, Ireland. hdoheny@nuigalway.ie
Lynch
Caoimhe M
CM
Smith
Terry J
TJ
Morrison
John J
JJ
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D002046:Bupranolol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D004983:Ethanolamines / Q000494:pharmacology; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D032342:Muscle Cells / Q000378:metabolism*; D009126:Muscle Relaxation / Q000187:drug effects; D009215:Myometrium / Q000166:cytology / Q000378:metabolism; D010121:Oxytocin / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism*; D011412:Propanolamines / Q000494:pharmacology; D022702:Receptors, Adrenergic, beta-3 / Q000378:metabolism*; D014590:Uterine Contraction / Q000187:drug effects / Q000502:physiology*; D014599:Uterus / Q000166:cytology / Q000378:metabolism*
C097869:3-(2-ethylphenoxy)-1-(1,2,3,4-tetrahydronaphth-1-ylamino)-2-propanol oxalate; D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D004983:Ethanolamines; D010455:Peptides; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; D011412:Propanolamines; D022702:Receptors, Adrenergic, beta-3; D010121:Oxytocin; C057368:BRL 37344; C064719:iberiotoxin; D002046:Bupranolol