Neutral metalloendopeptidase associated with the smooth muscle cells of pregnant rat uterus

1991 ◽  
Vol 45 (4) ◽  
pp. 401-411 ◽  
Author(s):  
Anna Ottlecz ◽  
Susan Walker ◽  
Matt Conrad ◽  
Barry Starcher
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Rat Uterus ◽  
Pregnant Rat

Fast Na+ channels in smooth muscle from pregnant rat uterus

1992 ◽  
Vol 70 (4) ◽  
pp. 491-500 ◽  
Author(s):  
Nicholas Sperelakis ◽  
Yoshihito Inoue ◽  
Yusuke Ohya
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Current Density ◽  
Sodium Current ◽  
Muscle Cells ◽  
Slow Inward Current ◽  
Rat Uterus ◽  
Pregnant Rat ◽  
Inward Current ◽  
Channel Current

Smooth muscle cells normally do not possess fast Na+ channels, but inward current is carried through two types of Ca2+ channels: slow (L type) Ca2+ channels and fast (T type) Ca2+ channels. Whole-cell voltage clamp was done on single smooth muscle cells isolated from the longitudinal layer of the 18-day pregnant rat uterus. Depolarizing pulses, applied from a holding potential of −90 mV, evoked two types of inward current, fast and slow. The fast inward current decayed within 30 ms, depended on [Na]o, and was inhibited by tetrodotoxin (TTX) (K0.5 = 27 nM). The slow inward current decayed slowly, was dependent on [Ca]o (or Ba2+), and was inhibited by nifedipine. These results suggest that the fast inward current is a fast Na+ channel current and that the slow inward current is a Ca2+ slow channel current. A fast-inactivating Ca2+ channel current was not evident. We conclude that the ion channels that generate inward currents in pregnant rat uterine cells are TTX-sensitive fast Na+ channels and dihydropyridine-sensitive slow Ca2+ channels. The number of fast Na+ channels increased during gestation. The averaged current density increased from 0 on day 5, to 0.19 on day 9, to 0.56 on day 14, to 0.90 on day 18, and to 0.86 pA/pF on day 21. This almost linear increase occurs because of an increase in the fraction of cells that possess fast Na+ channels. The Ca2+ channel current density was also higher during the latter half of gestation. These results indicate that the fast Na+ channels and Ca2+ slow channels in myometrium become more numerous as term approaches, and we suggest that the fast Na+ current may be involved in spread of excitation. Isoproterenol (β-agonist) did not affect either ICa(s) or INa(f), whereas Mg2+ (K0.5 = 12 mM) and nifedipine (K0.5 = 3.3 nM) depressed ICa(s). Oxytocin had no effect on INa(f) and actually depressed ICa(s) to a small extent. Therefore, the tocolytic action of β-agonists cannot be explained by an inhibition of ICa(s), whereas that of Mg2+ can be so explained. The stimulating action of oxytocin on uterine contractions cannot be explained by a stimulation of ICa(s).Key words: sodium current, fast sodium current, calcium currents, myometrial smooth muscle cells, pregnant uterine muscle.

An ATP-sensitive conductance in cultured smooth muscle cells from pregnant rat myometrium

1989 ◽  
Vol 257 (2) ◽  
pp. C297-C305 ◽  
Author(s):  
E. Honore ◽  
C. Martin ◽  
C. Mironneau ◽  
J. Mironneau
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Voltage Clamp ◽  
Free Acid ◽  
Muscle Cells ◽  
Monovalent Cation ◽  
Acid Form ◽  
Pregnant Rat ◽  
Free Acid Form ◽  
Cultured Smooth Muscle Cells

The whole cell voltage-clamp technique was used to study the effects of extracellular ATP in cultured smooth muscle cells isolated from pregnant rat myometrium. An inward current was elicited by ATP (IATP) in cells held at -70 mV under voltage clamp. The amplitude of IATP was reduced by estrogen pretreatment and by the end of pregnancy. IATP not only did not undergo any desensitization but showed facilitation. The current-voltage relationship of IATP was linear and reversed close to 0 mV. Changing the sodium electrochemical gradient by decreasing extracellular or intracellular sodium resulted in a linear relationship between the reversal potential of IATP and Na equilibrium potential that, however, differed from the predicted curve for a purely sodium conductance. The conductance activated by ATP was monovalent cation selective with little discrimination between potassium, cesium, and sodium ions. IATP was depressed by divalent cations, and the rank order of potency was Co greater than Mg greater than Ca greater than Ba, suggesting that the free-acid form of ATP was the effective ligand. Adenosine, AMP, and ADP were ineffective in eliciting IATP, whereas ATP gamma S and alpha,beta-methylene ATP were capable of mimicking the effects of ATP, although they were less potent. These results are consistent with the free-acid form of ATP activating a monovalent cation-selective and estrogen-sensitive conductance in myometrium.

Gestational change in Na+ and Ca2+ channel current densities in rat myometrial smooth muscle cells

1991 ◽  
Vol 260 (3) ◽  
pp. C658-C663 ◽  
Author(s):  
Y. Inoue ◽  
N. Sperelakis
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Reversal Potential ◽  
Cell Voltage ◽  
Muscle Cells ◽  
Linear Increase ◽  
Na Channels ◽  
Pregnant Rat ◽  
Spread Of Excitation ◽  
Current Densities

The change of Na+ and Ca2+ channel currents during gestation was investigated using the whole cell voltage-clamp method on single smooth muscle cells freshly isolated from the longitudinal layer of pregnant rat uterus. The current-voltage relationships for both the Na+ and Ca2+ currents did not change during gestation. The threshold voltage, the voltage at the peak inward current, and the reversal potential (extrapolated) were virtually identical. The averaged current densities of Ca2+ channel were almost unchanged between days 9 and 21; this value at day 5 was somewhat lower. In contrast, the averaged current density of fast Na+ channels increased markedly in the myometrium during gestation: from 0 at day 5 to 0.19 +/- 0.16 at day 9, to 0.56 +/- 0.13 at day 14, to 0.90 +/- 0.13 at day 18, and to 0.86 +/- 0.14 pA/pF at day 21. This almost linear increase in the averaged density of fast Na+ channels during gestation occurs because of an increase in the fraction of cells which possessed fast Na+ channels. These results suggest that the role of fast Na+ channels in myometrial activity becomes more and more important as term approaches. We suggest that the fast Na+ current may be involved in spread of excitation.

Forskolin inhibition of K+ current in pregnant rat uterine smooth muscle cells

1993 ◽  
Vol 240 (2-3) ◽  
pp. 169-176 ◽  
Author(s):  
Yoshihito Inoue ◽  
Keiichi Shimamura ◽  
Nicholas Sperelakis
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Pregnant Rat ◽  
Uterine Smooth Muscle ◽  
K Current
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