Sodium and Calcium Inward Currents in Freshly Dissociated Smooth Myocytes of Rat Uterus
Tóm tắt
Freshly dissociated myocytes from nonpregnant, pregnant, and postpartum rat uteri have been studied with the tight-seal patch-clamp method. The inward current contains both INa and ICa that are vastly different from those in tissue-cultured material. INa is abolished by Na+-free medium and by 1 μM tetrodotoxin. It first appears at ∼−40 mV, reaches maximum at 0 mV, and reverses at 84 mV. It activates with a voltage-dependent τ of 0.2 ms at 20 mV, and inactivates as a single exponential with a τ of 0.4 ms. Na+ conductance is half activated at −21.5 mV, and half inactivated at −59 mV. INa reactivates with a τ of 20 ms. ICa is abolished by Ca2+-free medium, Co2+ (5 mM), or nisoldipine (2 μM), and enhanced in 30 mM Ca2+, Ba2+, or BAY-K 8644. It first appears at ∼−30 mV and reaches maximum at +10 mV. It activates with a voltage-dependent τ of 1.5 ms at 20 mV, and inactivates in two exponential phases, with τ's of 33 and 133 ms. Ca2+ conductance is half activated at −7.4 mV, and half inactivated at −34 mV. ICa reactivates with τ's of 27 and 374 ms. INa and ICa are seen in myocytes from nonpregnant estrus uteri and throughout pregnancy, exhibiting complex changes. The ratio of densities of peak INa/ICa changes from 0.5 in the nonpregnant state to 1.6 at term. The enhanced role of INa, with faster kinetics, allows more frequent repetitive spike discharges to facilitate simultaneous excitation of the parturient uterus. In postpartum, both currents decrease markedly, with INa vanishing from most myocytes. Estrogen-enhanced genomic influences may account for the emergence of INa, and increased densities of INa and ICa as pregnancy progresses. Other influences may regulate varied channel expression at different stages of pregnancy.
Từ khóa
Tài liệu tham khảo
Amedee, 1987, The calcium channel current of pregnant rat single myometrial cells in short-term primary culture, J Physiol (Camb), 392, 253, 10.1113/jphysiol.1987.sp016779
Amedee, 1986, The presence of Na+channels in myometrial smooth muscle cells is revealed by specific neurotoxins, Biochem Biophys Res Commun, 137, 675, 10.1016/0006-291X(86)91131-9
Anderson, 1971, Studies in calcium and sodium in uterine smooth muscle excitation under current-clamp and voltage-clamp conditions, J Gen Physiol, 58, 322, 10.1085/jgp.58.3.322
Bolton, 1985, Patch and whole-cell voltage-clamp of single mammalian visceral and vascular smooth muscle cells, Experientia (Basel), 41, 887, 10.1007/BF01970006
Frankenhauser, 1957, The action of calcium on the electrical properties of squid axon, J Physiol (Camb), 137, 218, 10.1113/jphysiol.1957.sp005808
Hamill, 1981, Improved patch-clamp technique for high-resolution current recording from cells and cell-free membrane patches, Eur J Physiol, 391, 85, 10.1007/BF00656997
Inoue, 1991, Gestational change in Na+ and Ca2+channel current densities in rat myometrial smooth muscle cells, Am J Physiol, 29, C658, 10.1152/ajpcell.1991.260.3.C658
Inoue, 1990, Some electrical properties of human pregnant myometrium, Am J Obstet Gynecol, 162, 1090, 10.1016/0002-9378(90)91322-4
Isenberg, 1982, Calcium tolerant ventricular myocytes prepared by preincubation in a “KB” medium, Pflügers Archiv, 395, 6, 10.1007/BF00584963
Kao, 1978, A calcium current in the rat myometrium, Jpn J Smooth Muscle Res (Suppl), 14, 9
Kao, 1975, Ionic currents in the uterine smooth muscle, J Physiol (Camb), 246, 1, 10.1113/jphysiol.1975.sp010878
Kao, 1989, The outward current of the isolated rat myometrium, J Physiol (Camb), 418, 20P
Klöckner, 1985, Calcium currents of cesium loaded isolated smooth muscle cells (urinary bladder of the guinea pig), Pflügers Archiv, 405, 340, 10.1007/BF00595686
Mironneau, 1974, Voltage clamp analysis of the ionic currents in uterine smooth muscle using the double sucrose gap method, Pflügers Archiv, 352, 107, 10.1007/BF00590485
Miyoshi, 1991, Electrophysiological properties of membrane currents in single myometrial cells isolated from pregnant rats, Eur J Physiol, 419, 386, 10.1007/BF00371121
Mollard, 1986, Electrophysiological characterization of single pregnant myometrial cells in short-term primary culture, Am J Physiol, 250, C47, 10.1152/ajpcell.1986.250.1.C47
Nakai, 1983, Changing proportions of Na+ and Ca2+components of the early inward current in rat myometrium during pregnancy, Fed Proc, 42, 313
Ohya, 1989, Fast Na+ and slow Ca2+channels in single uterine muscle cells from pregnant rats, Am J Physiol, 257, C408, 10.1152/ajpcell.1989.257.2.C408
Piedras-Renteria, 1991, Potassium currents in freshly dispersed myometrial cells, Am J Physiol, 251, C278, 10.1152/ajpcell.1991.261.2.C278
Rendt, 1992, Progesterone increases Ca2+currents in myometrial cells from immature and nonpregnant adult rats, Am J Physiol, 31, C293, 10.1152/ajpcell.1992.262.2.C293
Sui, 1997, Properties of inward calcium current in guinea pig ureteral myocytes, Am J Physiol, 273, C543, 10.1152/ajpcell.1997.272.2.C543
Sui, 1993, Ca2+influx during action potentials of smooth myocytes of guinea pig urinary bladder, Biophys J, 64, A364
Suput, 1989, Ionic currents in freshly dispersed rat myometrial cells, FASEB J, 3, A254
Toro, 1990, Hormonal regulation of potassium currents in single myometrial cells, Proc Natl Acad Sci USA, 87, 2892, 10.1073/pnas.87.8.2892
Wang, 1993, Ionic currents in the uterine myocyte during pregnancy, Biophys J, 64, A366
Wang, 1996, Pregnancy and K+currents of freshly dissociated rat uterine myocytes, Biophys J, 70, A396
Yamamoto, 1989, Inward current in single cells of the guinea pig taenia coli, J Gen Physiol, 93, 521, 10.1085/jgp.93.3.521
Yang, 1994, Regulation by ovarian hormones of the large-conductance Ca2+-activated K+channels of freshly dissociated rabbit uterine myocyte, Biophys J, 66, A436
Yoshino, 1989, Ionic currents in smooth myocytes of the pregnant rat uterus, J Gen Physiol, 94, 38
Yoshino, 1990, Inward current in freshly dispersed rat myometrial cells, Biophys J, 57, 164A
Young, 1991, Characterization of sodium channels in cultured human uterine smooth muscle cells, Am J Obstet Gynecol, 164, 175, 10.1016/0002-9378(91)90650-G