title: Pregnancy modifies the large conductance Ca2+-activated K+ channel and cGMP-dependent signaling pathway in uterine vascular smooth muscle.
abstract: Regulation of uteroplacental blood flow (UPBF) during pregnancy remains unclear. Large conductance, Ca(2+)-activated K(+) channels (BK(Ca)), consisting of alpha- and regulatory beta-subunits, are expressed in uterine vascular smooth muscle (UVSM) and contribute to the maintenance of UPBF in the last third of ovine pregnancy, but their expression pattern and activation pathways are unclear. We examined BK(Ca) subunit expression, the cGMP-dependent signaling pathway, and the functional role of BK(Ca) in uterine arteries (UA) from nonpregnant (n = 7), pregnant (n = 38; 56-145 days gestation; term, approximately 150 days), and postpartum (n = 15; 2-56 days) sheep. The alpha-subunit protein switched from 83-87 and 105 kDa forms in nonpregnant UVSM to 100 kDa throughout pregnancy, reversal occurring >30 days postpartum. The 39-kDa beta(1)-subunit was the primary regulatory subunit. Levels of 100-kDa alpha-subunit rose approximately 70% during placentation (P < 0.05) and were unchanged in the last two-thirds of pregnancy; in contrast, beta(1)-protein rose throughout pregnancy (R(2) = 0.996; P < 0.001; n = 13), increasing 50% during placentation and approximately twofold in the remainder of gestation. Although UVSM soluble guanylyl cyclase was unchanged, cGMP and protein kinase G(1alpha) increased (P < 0.02), paralleling the rise and fall in beta(1)-protein during pregnancy and the puerperium. BK(Ca) inhibition not only decreased UA nitric oxide (NO)-induced relaxation but also enhanced alpha-agonist-induced vasoconstriction. UVSM BK(Ca) modify relaxation-contraction responses in the last two-thirds of ovine pregnancy, and this is associated with alterations in alpha-subunit composition, alpha:beta(1)-subunit stoichiometry, and upregulation of the cGMP-dependent pathway, suggesting that BK(Ca) activation via NO-cGMP and beta(1) augmentation may contribute to the regulation of UPBF.
authors.affiliation: Division of Neonatal-Perinatal Medicine, Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390, USA. charles.rosenfeld@utsouthwestern.edu
authors.forename: Charles R
authors.initials: CR
authors.lastname: Rosenfeld
authors.forename: Xiao-tie
authors.initials: XT
authors.lastname: Liu
authors.forename: Kevin
authors.initials: K
authors.lastname: DeSpain
mesh_terms: D000818:Animals; D001158:Arteries / Q000502:physiology; D006152:Cyclic GMP / Q000378:metabolism*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism; D005260:Female; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000235:genetics / Q000378:metabolism*; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits / Q000235:genetics / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D021041:Placental Circulation / Q000502:physiology; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012756:Sheep; D015398:Signal Transduction / Q000502:physiology*; D014599:Uterus / Q000098:blood supply*; D014664:Vasodilation / Q000502:physiology
chemical_list: D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits; D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP