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.

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 A Computational Model of the Ionic Currents, Ca2+ Dynamics and Action Potentials Underlying Contraction of Isolated Uterine Smooth Muscle

PLoS ONE ◽  
2011 ◽  
Vol 6 (4) ◽  
pp. e18685 ◽  
Author(s):  
Wing-Chiu Tong ◽  
Cecilia Y. Choi ◽  
Sanjay Karche ◽  
Arun V. Holden ◽  
Henggui Zhang ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Computational Model ◽  
Action Potentials ◽  
Ionic Currents ◽  
Uterine Smooth Muscle

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 Membrane Currents in Mammalian Ventricular Heart Muscle Fibers Using a Voltage-Clamp Technique

1971 ◽  
Vol 57 (3) ◽  
pp. 290-296 ◽  
Author(s):  
Gerhard Giebisch ◽  
Silvio Weidmann
Keyword(s):  
Action Potential ◽  
Outward Current ◽  
Time Dependent ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Initial Amplitude ◽  
Inward Current ◽  
Gap Technique ◽  
Sucrose Gap

Bundles of sheep ventricular fibers were voltage-clamped utilizing a modified sucrose gap technique and intracellular voltage control. An action potential was fired off in the usual way, and the clamp circuit was switched on at preselected times during activity. Clamping the membrane back to its resting potential during the early part of an action potential resulted in a surge of inward current. The initial amplitude of this current surge decreased as the clamp was switched on progressively later during the action potential. Inward current decreasing as a function of time was also recorded if the membrane potential was clamped beyond the presumed K equilibrium potential (to -130 mv). Clamping the membrane to the inside positive range (+40 mv to +60 mv) at different times of an action potential resulted in a step of outward current which was not time-dependent. The results suggest that normal repolarization of sheep ventricle depends on a time-dependent decrease of inward current (Na, Ca) rather than on a time-dependent increase of outward current (K).

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.

Ionic currents of smooth muscle cells isolated from the ctenophore Mnemiopsis

1988 ◽  
Vol 233 (1271) ◽  
pp. 99-121 ◽  
Keyword(s):  
Smooth Muscle ◽  
Steady State ◽  
Smooth Muscle Cells ◽  
Voltage Clamp ◽  
Muscle Cells ◽  
Ionic Currents ◽  
Patch Clamping ◽  
Excitable Cells ◽  
Inward Current ◽  
Electrode Voltage

The ionic currents of smooth muscle cells isolated from the ctenophore Mnemiopsis were examined by using conventional two-electrode voltage clamp and whole-cell patch clamping methods. Several separable currents were identified. These include: (1) a transient and (2) a steady-state voltage-activated inward current; both are tetrodotoxin (TTX) and saxitoxin (STX) insensitive, partly reduced by decreasing external Ca 2+ or Na + or by addition of 5 mM Co 2+ , D-600 or verapamil and are totally blocked with 5 mM Cd 2+ ; (3) an early, transient, cation-dependent, outward K + current ( I Kca/Na ); (4) a transient, voltage-activated, outward K + current provisionally identified as I A ; (5) a delayed, steady-state, voltage-activated outward K + current ( I K ) and (6) a late, transient, outward K + current which is blocked by Cd 2+ and evident only during long voltage pulses. Despite their phylogenic origin, most of these currents are similar to currents identified in many vertebrate smooth and cardiac muscle preparations, and other excitable cells in higher animals.

Substance P activates Cl− and K+ conductances in guinea-pig tracheal smooth muscle cells

1994 ◽  
Vol 72 (6) ◽  
pp. 705-710 ◽  
Author(s):  
Luke J. Janssen ◽  
Stephen M. Sims
Keyword(s):  
Smooth Muscle ◽  
Substance P ◽  
Guinea Pig ◽  
Smooth Muscle Cells ◽  
Voltage Clamp ◽  
Airway Smooth Muscle ◽  
Muscle Cells ◽  
Equilibrium Potential ◽  
Airway Smooth Muscle Cells ◽  
Inward Current

Substance P (SP) causes bronchoconstriction, but its effects on airway smooth muscle ion conductances are unknown. We investigated the effects of SP on single smooth muscle cells dissociated from guinea-pig trachealis. Under voltage clamp at −60 mV, SP evoked reversible contractions and inward current (ISP). ISP had a latency of approximately 1 s, reached a peak of 1039 ± 147 pA (n = 19) about 2 s after onset of application, and declined to baseline levels over the next 5–10 s. At more positive holding potentials (−25 and 0 mV), the inward current was decreased in magnitude and preceded by outward current. With 140 mM K+ in the electrode and Cl− equilibrium potential (ECl) of about 0 mV, ISP was outwardly rectifying and reversed at −11 ± 2 mV. When K+ currents were blocked using Cs+, the current–voltage relationship for ISP was linear and reversed at 3 ± 1 mV. The reversal potential was dependent on the Cl− gradient across the membrane. These results suggest that SP caused a transient activation of Cl− and K+ conductances. Following the initial transient inward current, SP caused a prolonged suppression of spontaneously active K+ currents. The findings that SP evoked contractions during voltage clamp at potentials at which voltage-dependent Ca2+ channels are not active, and that current oscillations were also evoked by SP, suggest that SP is acting through release of Ca2+ from internal stores. Furthermore, SP occluded the inward current evoked by acetylcholine, suggesting that the peptidergic and cholinergic signalling pathways converge. We conclude that SP releases Ca2+ from internal stores in guinea-pig airway smooth muscle cells, leading to activation of Cl− and K+ conductances, depolarization, and contraction.Key words: Ca2+-dependent conductances, spontaneous transient outward currents, acetylcholine.

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