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

Non-selective cation channel (NSCC) currents were identified in myometrial smooth muscle cells isolated from pregnant rats (day 18-20) using the whole-cell patch clamp method. NSCC currents had a linear current/voltage relationship and were time independent. Reduction of extracellular Na(+) substantially decreased the amplitude of NSCC currents, indicating that the NSCC is permeable to Na(+). NSCC currents were blocked by La(3+) and Gd(3+) with K(d) values of 2.2 and 1.0 micro M, respectively. The relative permeability of various monovalent cations for NSCC was estimated by measurement of the reversal potential. The relative permeability for K(+):Cs(+):Na(+):Li(+) was 1.3:1:0.9:0.8. NSCC also had a small, but detectable, permeability for Ca(2+). Extracellular Mg(2+) inhibited myometrial NSCC currents concentration dependently with a K(d) of 0.28 mM. The observed Mg(2+) block may reasonably explain the inhibitory effect of magnesium on uterine contractions in the treatment of pre-term labor. Our results suggest that the NSCC plays a role in the regulation of myometrial contractility.