  Using the quark-meson coupling model, we study the longitudinal response
function for quasielastic electron scattering from nuclear matter within
relativistic RPA. In QMC the coupling constant between the scalar meson and the
nucleon is expected to decrease with increasing nuclear density. Furthermore,
since the electromagnetic form factors of the in-medium nucleon are modified at
the same time, the longitudinal response function and the Coulomb sum are
reduced by a total of about 20% in comparison with the Hartree contribution.
