Melatonin receptor signaling in pregnant and nonpregnant rat uterine myocytes as probed by large conductance Ca2+-activated K+ channel activity.
The mRNAs of MT1 and MT2 melatonin receptors are present in cells from nonpregnant (NPM) and pregnant (PM) rat myometrium. To investigate the coupling of melatonin receptors to Gq- and Gi-type of heterotrimeric G proteins, we analyzed the activity of large-conductance Ca2+-activated K+ (BKCa) channels, the expression of which in the uterus is confined to smooth muscle cells. The melatonin receptor agonist 2-iodomelatonin induced a pertussis toxin (PTX)-insensitive increase in channel open probability that was blocked by the nonselective antagonist luzindole. The 2-iodomelatonin effect on channel open probability was suppressed by overexpression of the Gqalpha-inactivating protein RGS16 and the phospholipase C inhibitor U-73122. The activity of BKCa channels is differentially regulated by protein kinase A (PKA) in NPM and PM cells. Thus, the beta-adrenoceptor agonist isoprenaline inhibited the BKCa channel conducted whole-cell outward current (Iout) in NPM cells and enhanced Iout in PM cells. Additional application of 2-iodomelatonin antagonized the isoprenaline effect on Iout in NPM cells but enhanced Iout in PM cells. All 2-iodomelatonin effects on Iout were sensitive to PTX treatment and the PKA inhibitor H-89. We therefore conclude that melatonin activates both the PTX-insensitive Gq/phospholipase C/Ca2+ and the PTX-sensitive Gi/cAMP/PKA signaling pathway in rat myometrium.
Steffens
Frank
F
Institut für Pharmakologie für Pharmazeuten, Universitätsklinikum Hamburg-Eppendorf, Martinistrasse 52, D-20246 Hamburg, Germany.
Zhou
Xiao-Bo
XB
Sausbier
Ulrike
U
Sailer
Claudia
C
Motejlek
Karin
K
Ruth
Peter
P
Olcese
James
J
Korth
Michael
M
Wieland
Thomas
T
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D005260:Female; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008550:Melatonin / Q000031:analogs & derivatives* / Q000494:pharmacology; D008564:Membrane Potentials; D009215:Myometrium / Q000166:cytology / Q000378:metabolism*; D037342:Pertussis Toxin / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology*; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D044122:Receptor, Melatonin, MT1 / Q000235:genetics / Q000378:metabolism*; D044123:Receptor, Melatonin, MT2 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism
D051036:Large-Conductance Calcium-Activated Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D044122:Receptor, Melatonin, MT1; D044123:Receptor, Melatonin, MT2; C044556:2-iodomelatonin; D000242:Cyclic AMP; D037342:Pertussis Toxin; D017868:Cyclic AMP-Dependent Protein Kinases; D010738:Type C Phospholipases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D008550:Melatonin; D007545:Isoproterenol; D002118:Calcium