Electrophysiological properties of membrane currents in single myometrial cells isolated from pregnant rats

Abstract

The whole-cell voltage-clamp method was applied to single smooth muscle cells prepared from the longitudinal layer of the pregnant rat myometrium (17-20 days of gestation). It was found that the transient inward current mainly consists of Ca2+ current, because the removal of Ca2+ ions from the external medium and 10 microM nifedipine eliminated this inward current. Its steady-state inactivation curve was obtained by the standard method, in which the membrane potential of half inactivation and the slope factor were estimated to be -58.0 +/- 4.9 mV (n = 11) and 8.9 +/- 1.4 mV (n = 11), respectively. In a small number of preparations (in 2 out of 30 preparations), there remained a very fast inward current in Ca(2+)-free medium containing Mg2+. Tetrodotoxin (TTX, 10 microM) can can abolish this current, suggesting that the channel for this current is equivalent to the Na+ channel in nerve cells. Two major phases of outward currents were identified by voltage jumps from negative holding levels to more positive levels. The first phase was a fast transient outward current. This current remained intact after external tetraethylammonium (TEA, 20 mM) was added. Following the transient current, a large delayed rectified outward current reached its peak over a period of 50 ms and then decayed. The reversal potential for this outward current was determined by observing the change of polarity of the tail currents with the change in extracellular K+ concentration [( K+]o). The slope for the change of reversal potential per ten-fold change in [K+]o is 57.7 mV at more than 23.2 mM [K+]o, indicating that this current is mostly carried by K+ ions. Voltage-dependent inactivation of the delayed rectified outward current was determined by the standard method. The membrane potential for half inactivation and the slope factor were estimated to be -42.8 +/- 3.9 mV (n = 3) and 10.1 +/- 1.5 mV (n = 3), respectively. External TEA (20 mM) effectively eliminated the delayed rectified outward currents. Nifedipine (10 microM) suppressed not only Ca2+ current but also outward K+ currents.

Properties of voltage‐activated [Ca2+]i transients in single smooth muscle cells isolated from pregnant rat uterus

“…The mean maximal ICa density was calculated to be 6·3 ± 0·8 pA pF¢ (n = 10) when depolarization was applied from a holding potential of −80 mV. This value is similar to that reported by Miyoshi et al (1991) and Inoue & Sperelakis (1991) Three trains of ten 100 ms voltage pulses were applied at 30 s intervals. These trains were followed by aclamp conditions have been published, though much work has been done on other smooth muscles (Becker et al 1989;Ganitkevich & Isenberg, 1991;Kamishima & McCarron, 1996).…”

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

“… is first evident at and raw data tracings show peak activation within and almost completely inactivated within [27], [51]. In human myometrial cells, has a half-inactivation of and a slope factor of [19], [51].…”

Identification of a non-selective cation channel current in myometrial cells isolated from pregnant rats

“…In rat myometrial smooth muscle cells under whole-cell voltage clamp, two types of voltage-dependent K + current are distinguishable by their sensitivity to TEA or 4-AP (4-aminopyridine) [27,34]. In addition to these two K currents, a Ca-activated K + channel has also been reported using the inside-out patch clamp method [3].…”