Fig. 5. Analysis of endocytotic fission pore kinetics. In the left panels, the imaginary (Im) conductance component reflects membrane patch capacitance, whereas the real (Re) component reflects the patch conductance. A transient increase in Re immediately prior to endocytosis reflects the endocytotic fission pore. In the right panels, the endocytotic vesicle capacitance (C_v) and fission pore conductance (G_p) were calculated from Im and Re (see Materials and Methods). After formation, the reduction of fission pore conductance reflects either the constriction or lengthening of the pore. The kinetics of this was examined by fitting G_p with a single exponential decay function (solid line). As observed at the arrow marked (i), the fission pore is first detected as G_p decreases to a measurable level. From here, pore conductance decays (marked ii) and finally decreases abruptly to zero (at the arrow marked iii), representing closure of the fission pore and removal of the endocytotic vesicle from the patch membrane as indicated by the simultaneous decrease in C_v.