Cell-cell fusion induced by the hemagglutinin (HA)
spike-glycoprotein of influenza virus has been studied extensively
using transfected cells expressing the protein. The initial
fusion event is the formation of a small pore connecting the
two cells. Its appearance has been measured by sudden changes
in capacitance by whole cell patch clamp and more recently by
the sudden change in the fluorescence of a possibly
potential-sensitive fluorophore. Using a new design of fluorescence
video microscopy capable of capturing multiple images at differing
wavelengths of light simultaneously at video rates, this
fluorescence event is shown to follow exponential kinetics,
with a life time, τ, of approximately 350 ms.