Voltage-gated K+ currents in freshly isolated myocytes of the pregnant human myometrium

1. Voltage-gated K+ currents in human myometrium are not well characterized , and were therefore investigated, using the whole-cell patch clamp techniq ue, in freshly isolated myometrial smooth muscle cells from pregnant women at term. 2. Three types of voltage-gated K+ currents were identified. I-K1 was a 4-a minopyridine-insensitive current with a negative half-inactivation (V-0.5 = -61 to -67 mV) and negative activation characteristics (threshold between -60 and -40 mV) and slow kinetics. I-K2 was a 4-aminopyridine-sensitive cur rent (half-maximal block at similar to 1 mM) with relatively positive half- inactivation (V-0.5 = -30 mV) and activation characteristics (threshold bet ween -40 and -30 mV) and faster kinetics. I-K,I-A was a 4-aminopyridine-sen sitive current with a negative inactivation and very fast inactivation kine tics. 3. Both I-K1 and I-K2 were sensitive to high concentrations of tetraethylam monium (half-maximal block at similar to 3 mM) and low concentrations of cl ofilium (half-maximal block by 3-10 mu M). 4. I-K1 and I-K2 were unevenly distributed between myometrial cells, most c ells possessing either I-K1 (30 cells) or I-K2 (24 cells) as the predominan t current. 5. The characteristics of these currents suggest a possible function in the control of membrane potentials and smooth muscle quiescence in the pregnan t human myometrium.