The human myometrium is mainly relaxed during pregnancy, but, up to term, contractions become more coordinated and forceful in order to initiate delivery. Small conductance Ca2+-activated K+ channels (SK channels) in human myometrium have been shown to be downregulated in late pregnancy. The aim was to investigate the presence of SK2 and SK3 in the human myometrium from nonpregnant women, pregnant women at term, and pregnancies delivered preterm and, in addition, to characterize the time of downregulation of these channels. Using qRT-PCR, we observed significantly lower levels of mRNA for SK2 than for SK3 in the nonpregnant tissue. The mRNA levels of SK3 were significantly reduced in tissue from pregnancies at term and pregnancies resulting in preterm deliveries, whereas no downregulation for SK2 was observed. Western blotting confirmed the qRT-PCR results. Using immunohistochemical staining, both SK2 and SK3 were detected in endometrial glandular epithelium. We conclude that SK3 mRNA is downregulated early in pregnancy—at least among those that result in preterm deliveries. Furthermore, we find that SK channels are expressed not only in the uterine smooth muscle but also in the endometrial epithelium. 1. Introduction Preterm births (delivery before 37 weeks of gestation) account for 9.6% of all births worldwide [1], and the number appears to be rising [2]. Death of the infant due to a preterm birth accounts for 28% of all neonatal deaths globally [3] which makes the issue of a great importance. Treatment available at present is able to delay birth only by approximately 1-2 days, which most often is insufficient to avoid severe complications for the newborn. Thus, there is a need for new and more efficient methods for treatment, calling for improved knowledge regarding the factors contributing to premature delivery. Recently, focus has been on the K+ channels and their contribution to the quiescence of the myometrium during pregnancy. Through their role in hyperpolarization, the channels are able to modulate excitability and contractility of the muscle cell. Several potassium channels including KCNQ channels [4], ATP-sensitive potassium channels [5], stretch-activated two-pore potassium channels [6], and big conductance Ca2+-activated potassium channels [7, 8] have been identified in human myometrium, and most of these channels are downregulated during late pregnancy. The small conductance Ca2+-activated potassium channel (SK channels) comprise three members (SK1-3) [9]. SK3 has been described in mouse myometrium of genetically altered mice, where an
References
[1]
S. Beck, D. Wojdyla, L. Say et al., “The worldwide incidence of preterm birth: a systematic review of maternal mortality and morbidity,” Bulletin of the World Health Organization, vol. 88, no. 1, pp. 31–38, 2010.
[2]
M. Keller, U. Felderhoff-Mueser, H. Lagercrantz et al., “Policy benchmarking report on neonatal health and social policies in 13 European countries,” Acta Paediatrica, vol. 99, no. 11, pp. 1624–1629, 2010.
[3]
J. E. Lawn, K. Wilczynska-Ketende, and S. N. Cousens, “Estimating the causes of 4 million neonatal deaths in the year 2000,” International Journal of Epidemiology, vol. 35, no. 3, pp. 706–718, 2006.
[4]
L. A. Mccallum, S. L. Pierce, S. K. England, I. A. Greenwood, and R. M. Tribe, “The contribution of Kv7 channels to pregnant mouse and human myometrial contractility,” Journal of Cellular and Molecular Medicine, vol. 15, no. 3, pp. 577–586, 2011.
[5]
M. Curley, M. T. Cairns, A. M. Friel, O. M. McMeel, J. J. Morrison, and T. J. Smith, “Expression of mRNA transcripts for ATP-sensitive potassium channels in human myometrium,” Molecular Human Reproduction, vol. 8, no. 10, pp. 941–945, 2002.
[6]
I. L. O. Buxton, C. A. Singer, and J. N. Tichenor, “Expression of stretch-activated two-pore potassium channels in human myometrium in pregnancy and labor,” PLoS One, vol. 5, no. 8, Article ID e12372, 2010.
[7]
L. Gao, B. Cong, L. Zhang, and X. Ni, “Expression of the calcium-activated potassium channel in upper and lower segment human myometrium during pregnancy and parturition,” Reproductive Biology and Endocrinology, vol. 7, article 27, 2009.
[8]
R. N. Khan, S. K. Smith, J. J. Morrison, and M. L. J. Ashford, “Properties of large-conductance K+ channels in human myometrium during pregnancy and labour,” Proceedings of the Royal Society B, vol. 251, no. 1330, pp. 9–15, 1993.
[9]
M. K？hler, B. Hirschberg, C. T. Bond et al., “Small-conductance, calcium-activated potassium channels from mammalian brain,” Science, vol. 273, no. 5282, pp. 1709–1714, 1996.
[10]
C. T. Bond, R. Sprengel, J. M. Bissonnette et al., “Respiration and parturition affected by conditional overexpression of the Ca2+-activated K+ channel subunit, SK3,” Science, vol. 289, no. 5486, pp. 1942–1946, 2000.
[11]
A. Brown, T. Cornwell, I. Korniyenko et al., “Myometrial expression of small conductance Ca2+-activated K+ channels depresses phasic uterine contraction,” American Journal of Physiology, vol. 292, no. 2, pp. C832–C840, 2007.
[12]
S. L. Pierce, J. D. K. Kresowik, K. G. Lamping, and S. K. England, “Overexpression of SK3 channels dampens uterine contractility to prevent preterm labor in mice,” Biology of Reproduction, vol. 78, no. 6, pp. 1058–1063, 2008.
[13]
J. Mazzone and I. L. O. Buxton, “Changes in small conductance potassium channel expression in human myometrium during pregnancy measured by RT-PCR,” Proceedings of the Western Pharmacology Society, vol. 46, pp. 74–77, 2003.
[14]
J. N. Mazzone, R. A. Kaiser, and I. L. O. Buxton, “Calcium-activated potassium channel expression in human myometrium: effect of pregnancy,” Proceedings of the Western Pharmacology Society, vol. 45, pp. 184–186, 2002.
[15]
S. L. Pierce and S. K. England, “SK3 channel expression during pregnancy is regulated through estrogen and Sp factor-mediated transcriptional control of the KCNN3 gene,” American Journal of Physiology, vol. 299, no. 4, pp. E640–E646, 2010.
[16]
K. Noble, R. Floyd, A. Shmygol, A. Shmygol, A. Mobasheri, and S. Wray, “Distribution, expression and functional effects of small conductance Ca-activated potassium (SK) channels in rat myometrium,” Cell Calcium, vol. 47, no. 1, pp. 47–54, 2010.
[17]
D.V. Skarra, T. Cornwell, V. Solodushko, A. Brown, and M.S. Taylor, “CyPPA, a positive modulator of small-conductance Ca2+-activated K+ channels, inhibits phasic uterine contractions and delays preterm birth in mice,” American Journal of Physiology, vol. 301, pp. C1027–C1035, 2011.
[18]
S.T. Rosenbaum, J. Svalo, K. Nielsen, T. Larsen, J.C. Jorgensen, and P. Bouchelouche, “Immunolocalization and expression of small-conductance calcium-activated potassium channels in human myometrium,” Journal of Cellular and Molecular Medicine, vol. 16, no. 12, pp. 3001–3008, 2012.
[19]
M. L. Palmer, K. R. Schiller, and S. M. O'Grady, “Apical SK potassium channels and Ca2+-dependent anion secretion in endometrial epithelial cells,” Journal of Physiology, vol. 586, no. 3, pp. 717–726, 2008.
[20]
A. S？derman, M. S. Thomsen, H. H. Hansen et al., “The nicotinic α7 acetylcholine receptor agonist ssr180711 is unable to activate limbic neurons in mice overexpressing human amyloid-β1-42,” Brain Research, vol. 1227, no. C, pp. 240–247, 2008.
[21]
M. Absi, M. P. Burnham, A. H. Weston, E. Harno, M. Rogers, and G. Edwards, “Effects of methyl β-cyclodextrin on EDHF responses in pig and rat arteries; association between SKCa channels and caveolin-rich domains,” British Journal of Pharmacology, vol. 151, no. 3, pp. 332–340, 2007.
[22]
Y. Ren, L. F. Barnwell, J. C. Alexander et al., “Regulation of surface localization of the small conductance Ca2+-activated potassium channel, Sk2, through direct phosphorylation by cAMP-dependent protein kinase,” Journal of Biological Chemistry, vol. 281, no. 17, pp. 11769–11779, 2006.
[23]
V. T. Martin, “Ovarian hormones and pain response: a review of clinical and basic science studies,” Gender Medicine, vol. 6, no. 2, pp. 168–192, 2009.
[24]
D. Jacobson, D. Pribnow, P. S. Herson, J. Maylie, and J. P. Adelman, “Determinants contributing to estrogen-regulated expression of SK3,” Biochemical and Biophysical Research Communications, vol. 303, no. 2, pp. 660–668, 2003.
[25]
Y.C. Ruan, J.H. Guo, X. Liu et al., “Activation of the epithelial Na+ channel triggers prostaglandin E2 release and production required for embryo implantation,” Nature Medicine, vol. 18, pp. 1112–1117, 2012.
[26]
K.L. Hamilton and D.C. Devor, “Basolateral membrane K+ channels in renal epithelial cells,” American Journal of Physiology, vol. 302, pp. F1069–F1081, 2012.
