Abstract
Objective
To determine whether nifedipine inhibits capacitative calcium entry at clinically relevant concentrations using cultured human myocytes as a model for human myometrium.
Methods
Myocyte cultures were initiated from the myometrium of term pregnant women who underwent cesarean delivery. Paired cells were chosen for study. The cell of interest was stimulated by an intercellular calcium wave from the adjacent cell. In this fashion, release of sarcoplasmic reticulum (SR) calcium was accomplished with minimal disturbance of the plasma membrane and the subplasmalemmal space (SPS) of the cell studied. Depletion of the SR calcium stores by the calcium wave activated the capacitative calcium current, elevated calcium in the SPS, and activated calcium-activated potassium channels. A cell-attached patc clamp was used to monitor the outward current resulting from the calcium activation of these potassium channels. Calcium green-1 fluorescence was used to simultaneously monitor changes of the deep cytosolic calcium concentrations. Experiments were performed at varying concentrations of nifedipine (0–10 μmol/L).
Results
Nifedipine reduced outward potassium currents in a dose-dependent manner. Nifedipine at 100 nmol/L resulted in greater than a 50% reduction of outward current, indicating a significant inhibition of capacitative calcium entry at that concentration. Higher concentrations of nifedipine abolished outward current. Experiments designed to detect indirect effects of nifedipine on capacitative calcium entry were negative.
Conclusion
Nifedipine block of capacitative calcium entry occurred at concentrations similar to those required to block L-type voltage-activated calcium channels. These data suggest that block of capacitative calcium entry may be an important mechanism of action when nifedipine is clinically used for tocolysis of preterm labor.
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References
Sanborn B. Relationship of ion channel activity to control of myometrial calcium. J Soc Gynecol Investig 2000;7:4–11.
Oei SG, Mol BW, de Kleine MJ, Brolmann HA. Nifedipine versus ritodrine for suppression of preterm labor: A meta-analysis. Acta Obstet Gynecol Scand 1999;78:783–8.
Takemura H, Hughes AR, Thastrup O, Putney JW Jr. Activation of calcium entry by the tumor promoter thapsigargin in parotid acinar cells: Evidence that an intracellular calcium pool and not an inositol phosphate regulates calcium fluxes at the plasma membrane. J Biol Chem 1989;264:12266–71.
Monga M, Campbell DF, Sanborn B. Oxytocin-stimulated capacitative calcium entry in human myometrial cells. Am J Obstet Gynecol 1999;181:424–9.
Young RC, Schumann R, Zhang P. Intracellular calcium gradients in cultured human uterine smooth muscle: A functionally important subplasmalemmal space. Cell Calcium 2001;29:183–9.
Kiselyov K, Xu X, Mozhayeva G, Kuo T, Pessah I, Mignery G, et al. Functional interaction between InsP3 receptors and store-operated Htrp3 channels. Nature 1998;396:478–82.
Ma HT, Patterson RL, van Rossum DB, Birnbaumer L, Mikoshiba K, Gill DL. Requirement of the inositol trisphosphate receptor for activation of store-operated Ca2+ channels. Science 2000;287:1647–51.
van Rossum DB, Patterson RL, Ma HT, Gill DL. Ca2+ entry mediated by store depletion, S-nitrosylation, and TRP3 channels: Comparison of coupling and function, J Biol Chem 2000; 275:28562–8.
Kiselyov KI, Shin DM, Wang Y, Pessah IN, Allen PD, Muallem S. Gating of store-operated channels by conformational coupling to ryanodine receptors. Mol Cell. 2000;6:421–31.
Young RC, Zhang P. The mechanism of propagation of intracellular calcium waves in cultured human uterine myocytes. Am J Obstet Gynecol. In press.
Hoyo-Vadillo C, Castaneda-Hernandez G, Herrera JE, Vidal-Garate J, Salazar LA, Moreno-Ramos A, et al. Pharmacokinetics of oral nifedipine: Relevance of the distribution phase. J Clin Pharmacol 1989;29:251–6.
Young RC, Smith LH, McLaren MD. T-type and L-type calcium currents in freshly dispersed human uterine smooth muscle cells. Am J Obstet Gynecol 1993;169:785–92.
Hopf FW, Reddy P, Hong J, Steinhardt PA. A capacitative calcium current in cultured skeletal muscle cells is mediated by the calcium-specific leak channel and inhibited by dihydropyridine compounds. J Biol Chem 1996;271:22358–67.
Shmigol AV, Eisner DA, Wray S. The role of sarcoplasmic reticulum as a Ca2+ sink in rat uterine smooth muscle cells. J Physiol 1999;520:153–63.
van Breemen C, Chen Q, Laher I. Superficial buffer barrier function of smooth muscle sarcoplasmic reticulum. Trends Pharmacol Sci 1995;16:98–105.
Young RC. Tissue-level signaling and the control of uterine contractility: The action potential-calcium wave hypothesis. J Soc Gynecol Investig 2000;7:146–52.
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Supported by National Institutes of Health, Child Health, and Human Development Grant 1RO1HD 36373.
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Young, R.C., Schumann, R. & Zhang, P. Nifedipine Block of Capacitative Calcium Entry in Cultured Human Uterine Smooth-Muscle Cells. Reprod. Sci. 8, 210–215 (2001). https://doi.org/10.1177/107155760100800405
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DOI: https://doi.org/10.1177/107155760100800405