PACEMAKER CURRENT (HYPERPOLARIZATION-ACTIVATED INWARD CURRENT) IN ISOLATED SINGLE PREGNANT RAT UTERINE MYOCYTES

Abstract

Whole-cell patch clamp experiments were performed to examine the underlying currents to generate spontaneous activity in freshly isolated single longitudinal muscle cells of pregnant rat uterus (18-day gestation). Isolated single cells were spindle- or round-shaped (50-700 μm in length and 2-30 μm in diameter). The holding potential was -30 mV. Long-duration (3 sec) hyperpolarizing pulses were applied to -40 to -120 mV, in increments of 10 mV. Experiments were performed at room temperature (22℃). A hyperpolarization-activated inward current (I_f) was produced. Current density at -120 mV was -1.03±0.31 pA/pF (n=5). The average capacitance was 64.3±2.3 pF (n=8). The threshold potential for activation of I_f was about -50 to -60 mV. The reversal potential was -18.6±2.1 mV (n=4). In the presence of Cs⁺ (3 mM), the I_f current at -120 mV was decreased by 76.5±2.1% (P<0.01, n=5). These results indicate that the Cs⁺⁻sensitive hyperpolarization-activated inward current is present in the longitudinal muscle cells of pregnant rat uterus. This I_f current may contribute somewhat to the electrogenesis of the spontaneous activity.