scholarly journals Studies on Calcium and Sodium in Uterine Smooth Muscle Excitation under Current-Clamp and Voltage-Clamp Conditions

1971 ◽  
Vol 58 (3) ◽  
pp. 322-339 ◽  
Author(s):  
Nels C. Anderson ◽  
Fidel Ramon ◽  
Ann Snyder
Keyword(s):  
Smooth Muscle ◽  
Voltage Clamp ◽  
Current Clamp ◽  
Uterine Smooth Muscle ◽  
Gap Technique ◽  
Steady State Current ◽  
Sucrose Gap ◽  
High Concentrations ◽  
Muscle Calcium ◽  
Double Sucrose Gap Technique

The objective of these studies was to define the roles of calcium and sodium in uterine smooth muscle excitation. The double sucrose-gap technique was used for current-clamp and voltage-clamp experiments. It was shown that neither sodium nor calcium alone is capable of supporting excitation in estrogen-dominated uterine smooth muscle. Calcium dependence was explained in part by increased membrane "leakage" current in calcium-free solution and calcium control of the voltage dependence of the early transient conductance. High concentrations of TTX did not affect the magnitude of the peak transient current while La+++, Mn++, and Co++ greatly reduced or abolished it and decreased the steady-state current. From these and other data it was concluded that the regenerative mechanism in uterine smooth muscle has the functional characteristics of a single transient conductance channel whose activation requires the presence of both sodium and calcium. Insensitivity to TTX indicates that the molecular structure of the channel is unlike that in certain sodium-dependent systems, while the effects of La+++, Mn++, Co++, and Ca++ reveal a similar dependence of conductances on extracellular polyvalent cations.

scholarly journals Voltage-Clamp Studies on Uterine Smooth Muscle

1969 ◽  
Vol 54 (2) ◽  
pp. 145-165 ◽  
Author(s):  
Nels C. Anderson
Keyword(s):  
Smooth Muscle ◽  
Voltage Clamp ◽  
Ionic Currents ◽  
Equilibrium Potential ◽  
Membrane Action ◽  
Uterine Smooth Muscle ◽  
Gap Technique ◽  
Sucrose Gap ◽  
Internal Potential ◽  
Voltage Axis

These studies have developed and tested an experimental approach to the study of membrane ionic conductance mechanisms in strips of uterine smooth muscle. The experimental and theoretical basis for applying the double sucrose-gap technique is described along with the limitations of this system. Nonpropagating membrane action potentials were produced in response to depolarizing current pulses under current-clamp conditions. The stepwise change of membrane potential under voltage-clamp conditions resulted in a family of ionic currents with voltage- and time-dependent characteristics. In sodium-free solution the peak transient current decreased and its equilibrium potential shifted along the voltage axis toward a more negative internal potential. These studies indicate a sodium-dependent, regenerative excitation mechanism.

Oxytocin actions on voltage-dependent ionic channels in pregnant rat uterine smooth muscle cells

1992 ◽  
Vol 70 (12) ◽  
pp. 1597-1603 ◽  
Author(s):  
Yoshihito Inoue ◽  
Keiichi Shimamura ◽  
Nicholas Sperelakis
Keyword(s):  
Smooth Muscle ◽  
Voltage Clamp ◽  
Calcium Current ◽  
Uterine Contraction ◽  
Cell Voltage ◽  
Ionic Channels ◽  
Pregnant Rat ◽  
Uterine Smooth Muscle ◽  
Voltage Dependent ◽  
Sodium And Potassium

The effects of oxytocin, a uterotonic polypeptide hormone, on the voltage-dependent slow calcium, fast sodium, and potassium channel currents were studied using whole-cell voltage clamp of freshly isolated cells from late pregnant (18–21 day) rat myometrium. The calcium current was rapidly inhibited by oxytocin (about 25% inhibition at 20 nM) in a dose-dependent manner, and this inhibitory effect was completely reversible by washout. However, inhibition was not observed when barium was used as the charge carrier. Sodium current and potassium current were not modified by oxytocin, thus sodium and potassium currents may not play important roles in oxytocin-induced augmentation of uterine contraction. It is concluded that oxytocin stimulates uterine contraction by mechanisms other than augmentation of the voltage-dependent calcium current, e.g., by release of Ca from sarcoplasmic reticulum (by inositol trisphosphate) or by activation of a receptor-operated Ca channel. The inhibition of the slow calcium current may be induced by the elevation of [Ca]i.Key words: oxytocin, ionic channels, uterine smooth muscle, whole-cell voltage clamp, pregnant rat myometrium.

scholarly journals Quercetin affects uterine smooth muscle contractile activity in gilts

PLoS ONE ◽  
2021 ◽  
Vol 16 (7) ◽  
pp. e0252438
Author(s):  
Aleksandra Zygmuntowicz ◽  
Włodzimierz Markiewicz ◽  
Tomasz Grabowski ◽  
Artur Burmańczuk ◽  
Alla Vyniarska ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Cyclic Group ◽  
Reproductive Tract ◽  
Contractile Activity ◽  
Middle Part ◽  
Physiological Status ◽  
Uterine Smooth Muscle ◽  
Circular Layer ◽  
High Concentrations ◽  
Immature Group

Quercetin is a polyphenolic flavonoid occurring in leaves, stems, flowers and fruits of many plants. In traditional Chinese medicine, it is used as a natural therapeutic agent with a broad spectrum of activities (antioxidant, neuroprotective, anti-inflammatory, anticancer, antibacterial and antiviral). Moreover, quercetin affects function of the reproductive tract, however the knowledge of this activity is still fragmentary. Therefore, this study aimed to determine the influence of quercetin on the contractile activity of the porcine myometrium collected from immature (n = 6), cyclic (n = 6) and early pregnant (n = 6) gilts. Strips of the myometrium (comprising longitudinal and circular layer) were resected from the middle part of the uterine horns and the isometric contractions were recorded. After 60–90 min of preincubation, the strips were stimulated with quercetin in increasing (10−13–10−1 M) concentrations and the changes in the tension amplitude and frequency of contractions were measured. Quercetin decreased (P<0.01–0.001) the amplitude of contractions at concentrations 10−11–10−1 M and 10−10–10−1 M in cyclic and early pregnant groups, respectively. The frequency of contractions decreased in all groups but was the highest (at concentrations 10−11–10−1 M; P<0.05–0.001) in the cyclic group and the lowest (at concentrations 10−5–10−1 M; P<0.01) in the immature group. The tension decreased only in the cyclic group after quercetin administration in high concentrations (10−6–10−1 M; P<0.05–0.01). The results indicate that quercetin causes relaxation of the porcine uterine smooth muscle but this activity is strongly related to the physiological status of the gilts.

Oxytocin induces an inward current in pregnant rat myometrial cells

1994 ◽  
Vol 72 (7) ◽  
pp. 759-763 ◽  
Author(s):  
Keiichi Shimamura ◽  
Masumi Kusaka ◽  
Nicholas Sperelakis
Keyword(s):  
Smooth Muscle ◽  
Voltage Clamp ◽  
Cell Voltage ◽  
Induced Current ◽  
Pregnant Rat ◽  
Whole Cell ◽  
Inward Current ◽  
Uterine Smooth Muscle ◽  
Whole Cell Voltage Clamp ◽  
Voltage Dependent

The effects of oxytocin (OT) on holding current were studied in uterine smooth muscle cells freshly isolated from the longitudinal layer of 18–20 day pregnant rats, using the nystatin method of whole-cell voltage clamp. As we previously reported, the voltage-dependent Ca2+ current (L type) was partially inhibited by OT (about 30% inhibition at 1 μM). When the cells were held at the holding potential (HP) of −60 mV and the holding current was monitored, OT induced an inward current. The amplitude of this OT-induced current was 72 ± 26 pA (n = 27). When the cell was held at more positive potentials (HP 0 or +40 mV), the OT-induced current reversed direction, becoming outward. This current usually was long lasting (74% of cells responding to OT); a transient current was observed in 26% of the cells. In the absence of either Na+ or Ca2+ in the bath solution, OT induced an inward current (at HP −60 mV). However, the OT-induced current was absent when both of these ions were omitted from the bath. These results suggest that OT induces an inward current through receptor-activated nonselective cation channels. The resulting increase of intracellular Ca2+ may contribute to the inhibition of voltage-dependent Ca2+ current produced by OT. This OT-induced current may also play an important role for membrane depolarization and accompanying contraction produced by OT in pregnant rat myometrium.Key words: oxytocin receptor activated channel, uterine smooth muscle, pregnant rat myometrium, holding current, whole-cell voltage clamp.

Calcium and angiotensin tachyphylaxis in rat uterine smooth muscle

1975 ◽  
Vol 228 (5) ◽  
pp. 1423-1430 ◽  
Author(s):  
RJ Freer
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscles ◽  
Rabbit Aorta ◽  
Rat Uterus ◽  
Uterine Smooth Muscle ◽  
Normal Tissues ◽  
High Concentrations ◽  
The Relationship ◽  
Very High ◽  
Stimulation Of

Studies were carried out to investigate the relationship between extracellular Ca++ and the ability of a particular smooth muscle to develop tachyphylaxis to angiotensin II (AII). Stimulation of rat uterus by AII was found to be dependent on extracellular Ca++. Placing the tissue in 0 Ca++ completely blocked AII-induced contractions as did the presence of the "Ca++ antagonists" verapamil (10- minus 5M), SKF 525-A (10- MINUS 5M), tetracaine (10- minus 4M), Mn++ (8 times 10- minus 3M), or La-3+ (10- minus 3M). In addition, it is no longer possible to produce tachyphylaxis to AII in deplorazed rat uterus under conditions of pH and Ca++ concentration in which a normally polarized preparation would be unresponsive. Verapamil, on the other hand, was an even more effective antagonist of AII in depolarized preparations (ID50 of 10- minus 8M) than in normal tissues (ID50 of 2.0 times 10- minus 7M). Like the rat uterus, the smooth muscle of the guinea pig ileum also develops tachyphylaxis to AII, and the effect of this peptide was also blocked by 10- minus 5 M verapamil. Rabbit aorta, however, was found to be relatively resistant to both development of tachyphylaxis under conditions of low Ca++ and low pH and also to inhibition by even very high concentrations of verapamil (10- minus 4M). The results of these studies suggest that the Ca++ site involved in the tachyphylactic response to AII may be a physiologically important one in those smooth muscles in which movement of extracellular Ca++ contributes to the inward ion currents during excitation. Verapamil, however, appears to act at a common step in the excitation-contraction sequence in rat uterus. A working model of the interaction of AII with rat uterine smooth muscle is presented.

scholarly journals Selective modification of sodium channel gating in lobster axons by 2, 4, 6-trinitrophenol: Evidence for two inactivation mechanisms.

1975 ◽  
Vol 66 (6) ◽  
pp. 765-779 ◽  
Author(s):  
G S Oxford ◽  
J P Pooler
Keyword(s):  
Time Course ◽  
Sodium Currents ◽  
Voltage Range ◽  
Sodium Conductance ◽  
Gap Technique ◽  
Voltage Curve ◽  
Sucrose Gap ◽  
Sodium Inactivation ◽  
Kinetics Of ◽  
Double Sucrose Gap Technique

Trinitrophernol (TNP) selectively alters the sodium conductance system of lobster giant axons as measured in current clamp and voltage clamp experiments using the double sucrose gap technique. TNP has no measurable effect on potassium currents but reversibly prolongs the time-course of sodium currents during maintained depolarizations over the full voltage range of observable currents. Action potential durations are increased also. Tm of the Hodgkin-Huxley model is not markedly altered during activation of the sodium conductance but is prolonged during removal of activation by repolarization, as observed in sodium tail experiments. The sodium inactivation versus voltage curve is shifted in the hyperpolarizing direction as is the inactivation time constant curve, measured with conditioning voltage steps. This shift speeds the kinetics of inactivation over part of the same voltage range in which sodium currents are prolonged, a contradiction incompatible with the Hodgkin-Huxley model. These results are interpreted as support for a hypothesis of two inactivation processes, one proceeding directly from the resting state and the other coupled to the active state of sodium conductance.

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