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

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Abstract
1 Voltage-gated K+ currents in human myometrium are not well characterized, and were therefore investigated, using the whole-cell patch clamp technique, in freshly isolated myometrial smooth muscle cells from pregnant women at term. 2 Three types of voltage-gated K+ currents were identified. IK1 was a 4-aminopyridine-insensitive current with a negative half-inactivation (V0.5= -61 to -67 mV) and negative activation characteristics (threshold between -60 and -40 mV) and slow kinetics. IK2 was a 4-aminopyridine-sensitive current (half-maximal block at ≈1 mM) with relatively positive half-inactivation (V0.5= -30 mV) and activation characteristics (threshold between -40 and -30 mV) and faster kinetics. IK,A was a 4-aminopyridine-sensitive current with a negative inactivation and very fast inactivation kinetics. 3 Both IK1 and IK2 were sensitive to high concentrations of tetraethylammonium (half-maximal block at ≈3 mM) and low concentrations of clofilium (half-maximal block by 3-10 μM). 4 I K1 and IK2 were unevenly distributed between myometrial cells, most cells possessing either IK1 (30 cells) or IK2 (24 cells) as the predominant current. 5 The characteristics of these currents suggest a possible function in the control of membrane potentials and smooth muscle quiescence in the pregnant human myometrium.