Time-resolved admittance measurements provide the basis for studies sh
owing that membrane fusion occurs through the formation and widening o
f an initially small pore, linking two previously separated aqueous co
mpartments. Here we introduce modifications to this method that correc
t the cell-pipette (source) admittance for attenuation and phase shift
s produced by electrophysiological equipment. Two new approaches for s
etting the right phase angle are discussed. The first uses the displac
ement of a patch-clamp amplifier C-slow potentiometer for the calculat
ion of phase. This calculation is based on amplitudes of observed and
expected (theoretical) changes in the source admittance. The second ap
proach automates the original phase adjustment, the validity of which
we prove analytically for certain conditions. The multiple sine wave a
pproach is modified to allow the calculation of target cell membrane p
arameters and the conductance of the fusion pore. We also show how thi
s technique can be extended for measurements of the resting potential
of the first (voltage-clamped) membrane. We introduce an algorithm for
calculation of fusion pore conductance despite a concurrent change in
the resistance of the clamped membrane. The sensitivity of the capaci
tance restoration algorithm to phase shift errors is analyzed, and exp
erimental data are used to demonstrate the results of this analysis. F
inally, we show how the phase offset can be corrected ''off-line'' by
restoring the shape of the capacitance increment.