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.

These are the first data demonstrating that BK(Ca) are essential in the maintenance of basal UBF in the last third of ovine pregnancy.

Vascular smooth muscle (VSM) maturation is developmentally regulated and differs between vascular beds. The maturation and contribution of VSM function to tissue blood flow and blood pressure regulation during early gestation are unknown. The carotid artery (CA) contributes to fetal cerebral blood flow regulation and well being. We studied CA VSM contractility, protein contents, and phenotype beginning in the midthird of ovine development. CAs were collected from early (88 -101 day of gestation) and late (138 -150 day; term ϭ day 150) fetal (n ϭ 14), newborn (6 -8 day old; n ϭ 7), and adult (n ϭ 5) sheep to measure forces in endothelium-denuded rings with KCl, phenylephrine, and ANG II; changes in cellular proteins, including total and soluble protein, actin and myosin, myosin heavy chain isoforms (MHC), filamin, and proliferating cell nuclear antigen; and vascular remodeling. KCl and phenylephrine elicited age-and dose-dependent contraction responses (P Ͻ 0.001) at all ages except early fetal, which were unresponsive. In contrast, ANG II elicited dose responses only in adults, with contractility increasing greater than fivefold vs. that shown in fetal or neonatal animals (P Ͻ 0.001). Increased contractility paralleled age-dependent increases (P Ͻ 0.01) in soluble protein, actin and myosin, filamin, adult smooth muscle MHC-2 (SM2) and medial wall thickness and reciprocal decreases (P Ͻ 0.001) in nonmuscle MHC-B, proliferating cell nuclear antigen and medial cellular density. VSM nonreceptor-and receptor-mediated contractions are absent or markedly attenuated in midgestation and increase age dependently, paralleling the transition from synthetic to contractile VSM phenotype and, in the case of ANG II, paralleling the switch to the AT1 receptor. The mechanisms regulating VSM maturation and thus blood pressure and tissue perfusion in early development remain to be determined. myosin heavy chain isoforms; nonmuscle myosin; fetal development; receptor and nonreceptor function; smooth muscle growth; angiotensin II SMOOTH MUSCLE DEVELOPMENT normally proceeds in a wellorchestrated manner before and after birth (5,6,11,14,41,53). These changes occur in three phases: cellular differentiation, functional maturation, and growth (42). During differentiation, progenitor cells derived from the mesenchyme are transformed into immature smooth muscle cells (SMC) localized to either visceral or vascular sites. The subsequent maturational changes result in developmentally regulated improvements in specific organ or vascular function essential for the well being and growth of the developing fetus and newborn. For example, functional maturation of the ovine bladder and umbilical artery smooth muscle occurs early in development (4, 6). The former is required for maintenance of fetal fluid balance and establishment of amniotic fluid volume, which permit normal lung development. The latter is essential in the regulation of fetal oxygen and nutrient uptake from the maternal placental circulation and probably blood pressure (4, 32). In co...

Large conductance K + channels (BK Ca ) are expressed in uterine artery (UA) smooth muscle from nonpregnant and pregnant sheep and contribute to the regulation of basal vascular tone and responses to estrogen and vasoconstrictors. To determine if BK Ca are expressed in women and contribute to UA function, we collected UA from nonpregnant women (n=31) at elective hysterectomy and analyzed for subunit protein, localization with immunohistochemistry and function using endothelium-denuded rings. UA expresses BK Ca α-, β1-and β2-subunit protein. KCl and phenylephrine (PE, an α 1 -agonist) caused dose-dependent vasoconstriction (P<0.001), and UA precontracted with PE dose-dependently relaxed with sodium nitroprusside (SNP; P<0.001). Tetraethylammonium chloride (TEA, 0.2-1.0 mM), a BK Ca inhibitor, dose-dependently increased resting tone (P=0.004; 28±5.3% with 1.0 mM), enhanced PE-induced (10 −6 M) vasoconstriction (P<0.04), and attenuated SNP-induced relaxation at 1.0 mM (P=0.02). BK Ca are expressed in human UA and modulate vascular function by attenuating vasoconstrictor responses and contributing to nitric oxide-induced vasorelaxation.

Background Muscle loss is a sequela of severe burn and critical illness with bed rest contributing significantly to atrophy. We hypothesize that exercise will mitigate muscle loss after burn with bed rest. Materials and Methods Male rats were assigned to sham ambulatory (S/A), burn ambulatory (B/A), sham hindlimb unloading (S/H), or burn hindlimb unloading (B/H). Rats received a 40% scald burn or sham and were ambulatory or placed in hindlimb unloading, a model of bed rest. Half performed twice-daily resistance climbing. Hindlimb isometric forces were measured on day 14. Results Soleus mass and muscle function were not affected by burn alone. Mass was significantly lower in hindlimb unloading (79 vs.139 mg, p<0.001) and no exercise (103 vs.115 mg, p<0.01). Exercise significantly increased soleus mass in B/H (86 vs. 77mg, p<0.01). Hindlimb unloading significantly decreased muscle force in the twitch (31 vs. 12g, p<0.001), tetanic (55 vs. 148 g, p<0.001), and specific tetanic measurements (12 vs. 22 N/cm2, p<0.001). Effects of exercise on force depended on other factors. In B/H, exercise significantly increased twitch (14 vs. 8 g, p<0.05) and specific tetanic force (14 vs. 7 N/cm2, p<0.01). Fatigue index was lower in ambulatory (55%) and exercise (52%) versus hindlimb (69%, p=0.03) and no exercise (73%, p=0.002). Conclusions Hindlimb unloading is a significant factor in muscle atrophy. Exercise increased the soleus muscle mass, twitch, and specific force in this model. However, the fatigue index decreased with exercise in all groups. This suggests exercise contributes to functional muscle change in this model of disuse and critical illness.