PASSIVE MEMBRANE-PROPERTIES AND INWARD CALCIUM CURRENT OF HUMAN UTERINE SMOOTH-MUSCLE CELLS

Human myometrium was obtained at the time of cesarean delivery by means of excisional biopsy from the upper margin of the uterine incision through the lower uterine segment. Isolated smooth muscle cells were obtained by collagenase treatment. With the whole-cell patch clamp technique, voltage-clamp and current-clamp experiments were performed. Regenerative action potentials were seen in 3 mmol/L calcium bathing solution. Voltage-clamp experiments demonstrated the presence of transient inward currents and large outward currents. Inward currents were isolated with the use of tetraethylammonium ion as a blocking agent of outward current. In 3 mmol/L calcium inward current began at - 60 mV and maximum inward current occurred at -40 mV. Maximum inward current density during the rising phase of the action potential was 1.0-mu-A/cm2 in 3 mmol/L calcium and was unaffected by reduction of sodium concentration in the bathing solution.