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.
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1 November 1997
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November 01 1997
Sodium and Calcium Inward Currents in Freshly Dissociated Smooth Myocytes of Rat Uterus
M. Yoshino,
M. Yoshino
From the Department of Pharmacology, State University of New York Health Science Center, Brooklyn, New York 11203
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S.Y. Wang,
S.Y. Wang
From the Department of Pharmacology, State University of New York Health Science Center, Brooklyn, New York 11203
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C.Y. Kao
C.Y. Kao
From the Department of Pharmacology, State University of New York Health Science Center, Brooklyn, New York 11203
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M. Yoshino
From the Department of Pharmacology, State University of New York Health Science Center, Brooklyn, New York 11203
S.Y. Wang
From the Department of Pharmacology, State University of New York Health Science Center, Brooklyn, New York 11203
C.Y. Kao
From the Department of Pharmacology, State University of New York Health Science Center, Brooklyn, New York 11203
Address correspondence to Dr. C.Y. Kao, Department of Pharmacology (Box 29), SUNY Health Science Center, 450 Clarkson Ave., Brooklyn, NY 11203. Fax: 718-270-3309.
1
Abbreviations used in this paper: I-V, current–voltage; TEA, tetraethylammonium chloride; TTX, tetrodotoxin.
Received:
January 06 1997
Accepted:
September 12 1997
Online ISSN: 1540-7748
Print ISSN: 0022-1295
1997
J Gen Physiol (1997) 110 (5): 565–577.
Article history
Received:
January 06 1997
Accepted:
September 12 1997
Citation
M. Yoshino, S.Y. Wang, C.Y. Kao; Sodium and Calcium Inward Currents in Freshly Dissociated Smooth Myocytes of Rat Uterus . J Gen Physiol 1 November 1997; 110 (5): 565–577. doi: https://doi.org/10.1085/jgp.110.5.565
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